the effects of nest ectoparasites on cliff …
TRANSCRIPT
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THE EFFECTS OF NEST ECTOPARASITES ON
CLIFF SWALLOW POPULATIONS
by
BRIAN RICHARD CHAPMAN, B.S., M.S.
A DISSERATION
IN
ZOOLOGY
Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for
the Degree of
DOCTOR OF PHILOSOPHY
Approved
Accepted
May, 1973
%o\
(973 A , ,o ACKNOWLEDGEMENTS
My deepest appreciation is expressed to Dr. John
E. George for his intransmutable patience and sagacious
guidance during the course of this investigation. I
am indebted to the members of my committee. Dr. Eric
G. Bolen, Dr. Francis L. Rose, Dr. M. Kent Rylander,
and Dr. Russell W. Strandtraann, for their cooperation,
advice and criticism of the manuscript. Special acknow
ledgement is extended to Drs. Bart Cook III and Fred
G. Howell for their encouragement and collaboration in
the field research. Ms. Dede Armentrout, Mr. Jerry
Cooke, and Mr. Tony R. Mollhagen participated in various
field efforts. I am extremely grateful to Mr. Walter
Boron and his two sons, James and John, of Justiceburg,
Texas, for the unselfish provision of access to their
property and the interest they expressed. My wife.
Donna, also deserves gratitude for her assistance
during this study.
This dissertation was supported in part by Public
Health Service Research Grant No. AI-09591-03 from the
National Institutes of Allergy and Infectious Diseases
(Principal investigator: Dr. John E. George). Funds
were also provided by the Frank M. Chapman Memorial
Fund, American Museum of Natural History, a Grant-in-
Aid-of-Rosearch, The Society of the Sigma Xi, and
ii
The Graduate Student Development Fund, Texas Tech
University.
Information concerning clutch sizes of cliff
swallows was contributed by the North American Nest
Record Card Program, Laboratory of Ornithology, Cornell
University. Banding of cliff swallows was conducted
under permit 20055 of the Bird-banding Laboratory,
U.S. Department of the Interior, Fish and Wildlife
Service.
111
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ii
LIST OF TABLES v
LIST OF FIGURES vi
I. INTRODUCTION 1
II. METHODS AND MATERIALS 8
III. RESULTS 15
Arrival 15
Ectoparasite Populations 16
Clutch Size and Hatching Success . . 23
Nestling Growth 30
Blood Studios 42
Nestling Behavior . . . 46
Mortality Factors 48
IV. DISCUSSION 59
V. SUMMARY ^^
LITERATURE CITED 67
i v
UMMiH 'T^'^^v^-i^mfrmm^y , • ; » r - ---QS^^-
LIST OF TABLES
TABLE PAGE
1. The indexes of ectoparasite populations at the study colonies (1972) . . . . 22
2. Comparative population indexes for the 3 dominant ectoparasite species (1972) 24
3- Average clutch sizes at cliff swallow colonies 28
4. Number of eggs per nest. Data pooled for all study colonies 29
5- Per cent fledging success in the study colonies 32
6. A comparison of weights in natural and control colonies at the peak weight, day 23, and at fledging 36
7. A comparison of primary and rectrico lengths in natural and sprayed colonies at day 23 of nestling age 40
8. A comparison of the cellular elements of the blood per mm' in natural and sprayed colonies . . . . . 45
9' Mortality according to hatch sequence in ectoparasitized and sprayed colonies S5
10. Total mortality in the natural and sprayed colonies 57
LIST OF FIGURES
FIGURE PAGE
1. Artificial ectoparasite harborage . . . . 12
2. Average number of ectoparasites per harborage in each 5 day increment of the brooding season. Data from the 2 culvert bents are utilized for the comparison 18
3« Average number of ectoparasites per harborage in each 5 day increment of the brooding season. Data from the
j cliff sites are utilized for the
comparison 20
4. Daily per cent of nests with new eggs . . 26
5' Weight- growth curve based on moans for nestling cliff swallows in sprayed and natural colonies 3^
6. Weight growth curve for nestlings based on hatch sequence 38
7« Pattern of nestling disappearance from nests 50
VI
CHAPTER I
INTRODUCTION
Several species of homatophagous arthropods are
associated with the nesting colonies of the cliff
swallow, Petrochelidon pyrrhonota. throughout their
nesting range in western North America. This investiga
tion was conducted to determine the influence that these
ectoparasites exerted on the development and survival
of nestling cliff swallows and, hence, on cliff swallow
populations in northwestern Texas.
Cliff swallows spend the bulk of the year in South
America in an area that extends from southern Brazil
south to the central portions of Chile and Argentina
(A.O.U. 1957). The swallows migrate north in the
Spring and establish nesting colonies from central
Mexico north to central Canada and the Yukon.
Emlen (1941) described the requisites for poten
tial cliff swallow nesting sites: (1) a protected
vertical surface underneath an overhang; (2) an area
of reasonably open terrain for foraging in the immed
iate vicinity of the colony site; and (3) a readily
available supply of mud. The most suitable mud types
for nest construction are loams, clay-loams, and sandy-
loams rather than sandy or gravely soils (Buss 1942).
Grinnell and Miller (1944) added another cliff swallow
1
nesting site requirement: a permanent supply of
smooth-surfaced water for drinking.
Colonial aggregations form upon arrival at a
potential nesting site (Emlen 1954). Most of the
birds arrive at a particular colony site within a
24-hour period. However, there can be great variation
between the arrival times of neighboring colonies.
Mayhew (1958) concluded that a previous nesting ex
perience at a given site influenced migrational
homing. Adult birds which had a previous nesting
experience at a site returned first and occupied the
central nests in a colony. Yearling birds were fre
quently displaced when peripheral nest locations
were not available. Social interactions during colony
formation have been described by Emlen (1952). Pair
formation begins upon arrival at a potential colony
site and the paired birds cooperate in nest construction.
Nest construction and territory formation have been
discussed in detail by Emlen (1954).
Cliff swallows are determinate layers (Davis 1955),
with clutch size rarely exceeding five eggs (Samuel 1971).
Eggs are laid on consecutive days. The incubation
period, measured from the day the last egg was laid
until all eggs hatch, varies around 15 days. The
period from hatching to fledging is approximately 24
3
days (Myres 1957, Samuel 1971). A cursory study of
weight gain and feather growth of nestling cliff swallows
was conducted by Stoner (1945).
Nest sites are frequently abandoned for an in
definite period after 2 or 3 consecutive years of
usage (Grinnell, et al., 1930, Grinnell 1937).
Grinnell mentioned several factors that may contribute
to the alternate use of nesting sites: (1) the de
terioration of nests or nesting surfaces; (2) increased
predation upon swallows by other birds; (3) the ex
haustion of vitally necessary food elements within
the cruising radius of the foraging swallow; (4) an
intrinsic factor that leads the young of each succeeding
generation to establish separate nesting sites that are
utilized only during the life span of the cohort;
and (5) an accumulation of sizeable parasite popula
tions about the nests. Several authors (Stoner 1939;
Buss 19^2, Foster 1968, Samuel 1969a, 1969b, 1971) have
also noted that other birds may occupy cliff swallow
nests and cause extensive mortality and nest abandon
ment among cliff swallows.
Cliff swallows arrive in northwestern Texas in
mid-April and remain until late July or early August.
Their retort-shaped mud nests are constructed along the
escarpment of the High Plains caprock (Llano Estacado),
4
on the sandstone cliffs of the Brazos River tributaries,
on the undersides of concrete bridges, culverts and
dams and occasionally under the eaves of buildings
or inside of open barns.
A number of vertebrates are known to utilize
northwestern Texas cliff swallow domiciles for roosting
or nesting. Several species of bats, particularly
Tadarida brasiliensis, Eptesicus fuscus, Myotis velifer
and Pipestrellus subflavus, may be found in nests when
swallows are absent. English sparrows, Passer domesticus,
actively compete with cliff swallows for summer nesting
usage of the mud nests (Foster I968) and also utilize
the nests as winter roosting sites. English sparrows
are more commonly found associated with bridge sites
than cliff sites. In addition to overt competition,
the vertebrate nest associates contribute to the
maintenance of ectoparasite populations during the
winter months (Cook 1972).
The ectoparasites seek harborage in the inter
stices of the mud nests and in the crevices and fissures
commonly associated with sandstone cliff surfaces.
Additional ectoparasites may be introduced by the
cliff swallows (Foster and Olkowski I968). The hema-
tophagous arthropods associated with cliff swallow
colonies have been reported by several authors: fleas
5
(Eads 1956, Wheeler £t al. 1970); other insects (Hicks
1959)» and acarines (Baerg 1944, Kohls and Ryckman I962,
Howell and Chapman unpubl. MS). In northwestern Texas
cliff swallow colonies the populations of three ecto-
parasitic species reach significant proportions: the
swallow bug, Oeciacus vicarius; the swallow tick, Argas
cooleyi; and another tick, Ornithodoros concanensis.
There is evidence from several studies that ecto
parasites can have consequential effects on the mor
tality level and developmental rates of nestlings.
Moss and Camin (1970) demonstrated that parasitized
purple martin young weigh less at fledging and have
lower survival potential than parasite-free nestlings.
High parasite populations also resulted in a higher
percentage of nest and egg abandonment. Ticks have
caused mortality in several avian species by affecting
eyesight (Thomas 19^1, Worth 1942) and general phy
sical condition (Putzig 1939)' The effects of high
levels of ectoparasitism with concomitant blood loss
include changes in the cellular fractions and hemoglobin
concentrations in the blood. Certain ectoparasites of
domestic fowl have been shown to produce an anemic state
in the host (Olson 1935). Jellison and Kohls (1938),
working with experimental populations, suggested
that tick-host anemia is not only an experimental
6
disease but occurs with some frequency in nature and
may be the immediate cause of death in some animals.
In addition to direct damage caused by the loss of
blood, destruction of tissue and allergic responses,
ectoparasites may transmit a variety of damaging
epizootic diseases to their avian hosts (Philip, et al.
1935, Locke, et al. I962, Moss 1972). Two arboviruses
have been recently isolated from A. cooleyi associated
with northwestern Texas cliff swallow colonies (Yunker,
et. al. 1972) and it is possible that these agents cause
appreciable mortality.
This study was undertaken to ascertain if ecto
parasites have a demonstrable effect on cliff swallow
populations particularly in terms of the rate of
development and mortality among nestlings. The effects
of ectoparasites on cliff swallows were measured by
comparing population and nestling growth rate para
meters between normally parasitized colonies and
colonies in which chemical parasite control methods
were utilized. The parameters compared included clutch
size, hatching success, fledging success, mortality
and productivity. Rates of growth in certain flight
feathers, bones and weight were utilized to determine
the effect of ectoparasites on individual nestlings.
In addition an analysis of cellular and hemoglobin
7
components of blood samples from young swallows in
the treated and untreated sites provided an index to
specific effects of the feeding activity of ticks and
swallow bugs. The behavior of nestlings was also
studied in relation to mortality.
.•rTfi^.F-7m^^TOTTg;-^'nT:;^"Ti-i.;jp777m^-n^ I mii*.t(tf*>lmm
CHAPTER II
METHODS AND MATERIALS
Cliff swallow colonies studied were located in the
canyons or on highway culverts of the Double Mountain
Fork of the Brazos River or its tributaries in the
vicinity of Justiceburg, Garza County, Texas. Three of
the colonies were situated within 0.3 km south of the
river on the sandstone cliffs of Rocky Creek. The
sites were designated RC-1, RC-2, and RC-3 in order
approaching the river. Two of the sites were located
on the cliffs of the river itself. Four other river
colonies in the area were utilized by cliff swallows
but were inaccessable for nest study. The complex of
cliff sites mentioned above was located within a 0.3 km
diameter located 4.3 km ESE of Justiceburg. A sixth
study colony was located under a double-bent culvert
along a highway (Texas FM 2458) approximately 0.6 km E
of Justiceburg.
The intent was to study the development and sur
vival of nestling cliff swallows in both normal and
artificial colonies. The design of the artificial
colonies would have permitted accurate assessments of
ectoparasite concentrations, efficient ectoparasite
control and convenient access to the nest contents.
Study of the normal cliff situated nests was more
8
—"'7.=TfT:-7innniiiB3siHiiH!iiHaj; LITUUZL;;
9
difficult in terms of nest access and ectoparasite
control, but allowed natural parasite population
increases at untreated sites.
Prior to the 1971 arrival of cliff swallows, 2
artificial colonies were constructed and placed adjacent
to 2 normal, cliff-situated colonies on Rocky Creek
(RC-1 and RC-2). These sites were chosen because the
artificial colonies could be erected easily and the
sites were far from normal human passage. Each artificial
colony consisted of 0.9 X 2.4 m plywood sheets fitted
with 50 plaster nests which were constructed using
latex molds of several natural cliff swallow nests.
Trap doors behind each nest provided access to the
contents. Although cliff swallows nested in the
adjacent cliff colonies in 1971, only one pair of birds
laid eggs in an artificial nest.
One cliff site along the Brazos River and one bent
of the culvert were selected as treatment sites. The
treatment sites were sprayed twice v/eekly with Dibrom ,
a short-life acaricide, that according to Moss and Camin
(1970) is not toxic to avian hosts. The acaricide was
diluted to 1 part per 170 parts water and was applied
as a fine mist onto the nests and nest substrate with
an air-pressure type garden sprayer from a distance of
about 1 m. The nests and surrounding substrate were
10
lightly moistened with the acaricide. "Stickem" "'"
(polymerized butene, isobutene, and butane) was spread
around the circumference of the sprayed colonies to
hinder immigration of ectoparasites from neighboring
colonies.
No accurate method for estimating total ectoparasite
populations at a given site was ever devised. However,
artificial ectoparasite harborages provided a basis to
comparatively index tick and swallow bug populations.
The harborages (FIG. 1), molded from plaster of Paris,
were attached to the cliff face 10 cm below the study
colonies. A bolt, mounted in the cliff, ran through the
central hole in the harborage and the harborage was held
in place by a wing-nut. The recessed area in the har
borage provided a dark crevice into which ectoparasites
moved after obtaining a blood meal and leaving the
nests. The harborages were removed daily and counts
were made of the number of each species per trap.
After the count, the ectoparasites were removed and were
released near the base of the cliff.
In each study colony, 50 nests were individually
marked with spray enamel in a double color code. Care
• Michel & Pelton Co., Emeryville, California
11
FIGURE 1. Artificial ectoparasite harborage
12
side I ' I I I
T T
iz^ussaaaium-
13
was taken to mark an equal number of occupied central
and peripheral nests. In I971 each hatchling was
individually numbered on the back with a felt tip pen.
However, feather growth soon obscured the markings.
Therefore, in 1972 colored cloth-tape tarsal bands were
substituted. Prior to fledging serially numbered metal
bands provided by the Bird-banding Laboratory of the
U.S. Fish and Wildlife Service, were substituted for
the cloth bands.
On alternate days each nestling was removed from
the nest and was weighed on a balance sensitive to l/lO
gm. The tarsus and selected feathers were measured
to the nearest mm and notes were taken on the develop
ment of feather tracts, and plumage characteristics.
In addition to the above, every fourth day blood
samples were taken and the blood was analyzed in
several ways. Hemoglobin concentration was determined
with a Spencer Serial lOlOD Hemoglobinometer and measured
in gm Hb per 100 ml blood. Three trials were made per
drop of blood and the mean of the trials recorded. A
second drop of blood was utilized to make a thin smear
on a glass slide. To make differential blood counts, the
blood smears were dried and later stained with Wright's
staining solution. A third portion of blood was
collected in a heparinized micro-hematocrit tube. The
14
tube ends were sealed with plasticene and the tubes
were stored for a short time in a container surrounded
with ice. The tubes were spun for 5 minutes at 11,500
rpm in an International Micro-capillary Centrifuge
before measuring the hematocrit.
Observations were made of nestling behavior and
particular attention was given to the ontogeny of
behavior that would possibly influence the mortality
rate. The patterns studied included gaping, defecation,
"fear" responses and nestling dominance.
Intercolony associations of cliff swallows were
also noted in an attempt to assess intercolony parasite
transfer. Intercolony loafing, sunning, and mud gather
ing sites were examined for free ectoparasites.
: rrUJZl ZZ Zl TrxfTTf-CTT^TiTaTi-TJTTTrTJT:
CHAPTER III
RESULTS
Arrival
During the study, the first cliff swallows observed
in the Justiceburg area arrived on 25 March 1970, 17 March
1971 and 2 April 1972. Cliff swallows in the Justiceburg
area typically arrived first in small groups of about
3 or 4. These small groups apparently were the precursors
of distinct flocks. The movements of each flock for a
period of about a week became concentrated around 1 or
more potential nesting sites.
Just prior to site selection, a flock flew for
several hours a day in a tight vortex about a prospective
site and periodically landed on extant nests and nest
remnants. Some birds entered the nests. This behavior
was most pronounced in the evening and the birds roosted
in the nests. Copulation took place during these initial
stages of nest occupancy and territory formation. Nest
construction occurred for approximately a week. Colonial
memberships were tenuous during early colony formation.
In 1971 the wingtips of 25 birds from one colony were
sprayed with green enamel. A week later, 3 of the marked
birds occupied completed nests in a colony 0.2 km away
and two marked swallows were in a colony O.3 km distant.
15
16
Birds continued to join colonies for an indefinite
period after site selection.
Ectoparasite Populations
Early in the nest construction phase, the paired
birds began to occupy the nests at night. Egg laying
and incubation were usually initiated just prior to
nest completion. The presence of cliff swallows at a
colony site in some manner "activated" the endemic ecto
parasite populations. Prior to the arrival of the
swallows, only a few active ectoparasites were observed
on the nests or the cliff substrate. However, as soon
as the swallows began to occupy the nests at a site
the number of ectoparasites engaged in activity about
the nests increased dramatically.
Ectoparasite populations, as measured using the
artificial harborages, increased with the length of
cliff swallow tenure at the culvert (FIG. 2). A similar
pattern was noted at the cliff sites, but data from
the early stages of nesting were not available (FIG. 3).
The accumulation of ectoparasites about the nests in
creased to a peak that corresponded temporally to the
fledging period. The initial increases in apparent
ectoparasite density may have been a function of
increased tick and swallow bug feeding activity. Later
population increases resulted from reproductive addition
FIGURE 2. Average number of ectoparasites per harborage in each 5 day increment of the brooding season. Data from the 2 culvert bents are utilized
for the comparison.
•r.iyv:?rnmm^iri-:-r:-'- • - sii*
18
L J Natural
60-
50 -
4 0 -M
M « « a ^ 30 o
.a E 3
* 20 H
10-
Sprayed • fledge period
10 15 20 25 30
Days from hatch
35
FIGURE 3. Average number of ectoparasites per harborage in each 5 day increment of the brooding season. Data
from the cliff sites are utilized for the comparison.
80-
L - J Natura l
Sprayed
20
fledge period
70-
60-
« 50-
M
10
a
«
E 3
z
40-
10 15 20 25 30 35
Days from hatch
21
as a large nximber of larval and nymphal ectoparasites
was noted.
Ectoparasite populations in general and, specifically,
tick populations were much lower in bridge colonies at
the start of the season. There was reason to believe
that lower endemic populations at the beginning of the
season resulted in lower ectoparasite accumulations
throughout the season. For example, the mean number per
harborage of ectoparasites collected daily in the
artificial harborages was much higher (87 vs 46) at
the Point, an untreated cliff colony, than at the non-
sprayed culvert bent.
A comparison of the ectoparasite populations in all
of the natural and chemically controlled sites is shown
in TABLE 1. The number of ectoparasites per trap per
night was calculated to determine the ectoparasite index.
The site designated as the Point had the largest concen
tration of parasites. The Point was utilized in 1970 by
a large aggregation of swallows and probably possessed
the largest endemic population of A. cooleyi and Oeciacus
vicarus.
The total ectoparasite indexes of the sprayed and
natural sites were subjected to a Chi-square test for
independence. The resultant X^ of 10.14 (1 df) indicated
that there was a highly significant (P<0.01) difference
-"•'"-""• ' '
22
TABLE 1. The indexes of ectoparasite populations at
the study colonies (I972).
NATURAL
Point
Rocky Creek 3
Culvert 1
SPRAYED
Cliff
Culvert 2
Trap Nights
108
38
24
46
76
32
44
Total Ecto
parasites
1171
849
118
204
53
14
39
Ectoparasite Index
10.84 **
22.34
4.92
4.43
0.70 **
0.44
0.88
** YT = 10.14 (P<0.01) 1 df.
23
in the sizes of ectoparasite aggregations.
The swallow bug was the most abundant of the three
dominant ectoparasite species at most of the study colonies
(TABLE 2). Of the ticks, A. cooleyi was found in the
greatest concentrations particularly at the Point col
ony. Argas cooleyi appeared to be particularly sensitive
to the Dibrom. Following treatment a few swallow bugs
and Ornithodoros concanensis were seen, but A. cooleyi
was absent (TABLE 2). Aggregations of Oeciacus vicarus
were significantly reduced by the spray, but their
numbers tended to increase during the periods between
spray treatments. Populations of Ornithodoros concanensis
were small initially and did not show significant re
duction in the sprayed colonies.
The occurrence of ticks and swallow bugs at inter
colony loafing and mud gathering sites at Justiceburg was
regarded as evidence that ectoparasitic exchange between
colonies may occur.
Clutch Size and Hatching Success
A single egg was laid on consecutive days until
clutch completion. Egg laying data for the 6 Justiceburg
study sites were pooled in FIG. 4 to determine the degree
of laying synchrony. The percentage of marked nests
having new eggs each day was calculated. Egg laying in
24
TABLE 2. Comparative population indexes for the 3
dominant ectoparasite species (1972).
NATURAL
Point
Rocky Creek-3
Culvert 1
SPRAYED
Cliff
Culvert 2
Argas cooleyi Index
^.53
12.26
0.79
0.09
0.00
0.00
0.00
Ornithodoros concanensis
Index
0.15
0.37
0.04
0.02
0.04
0.06
0.02
Oeciacus vicarius Index
6.17
9.71
4.08
4.33
0.66
0.38
0.86
25
FIGURE 4. Daily per cent of nests with new eggs. Data
from all study colonies were pooled.
26
HHIHI
27
northwestern Texas occurred largely within an 8 day
period indicating intracolony synchrony. The majority
of eggs {7k.6fo) were laid in a 5 day period in each
colony (days 3-7 of the laying period).
Average clutch sizes for the Justiceburg colonies
are shown in TABLE 3* Included on this table are data
contributed by the North American Nest Record Card Pro
gram from Colorado (collected by W.C. Anderson, I967,
Otero County, Colorado) and Michigan (collected by E.
Kenega, 1957, Midland County, Michigan). Mean clutch
sizes ranged from 3*11 to 3.81 in this study. No
statistical difference was obtained in first and second
clutch size. To compare these data to those reported
in the literature, the percentage of nests in the Texas
study colonies having each possible clutch size is
given in TABLE 4. The majority of nests contained
3 or 4 eggs.
Intermittent incubation began after the first egg
was laid. Both the male and female spent the night in
the nest and may have alternated during the day to in
cubate the eggs. The incubation period, measured from
the day the last egg was laid until all eggs hatched,
varied from 15 to I6 days, 15 days being the mode
(97.3^).
Hatching success varied with clutch size. From
clutches of 4 eggs, 84 per cent of the eggs hatched;
28
TABLE 3* Average clutch sizes at cliff swallow colonies.
FIRST CLUTCH
Rocky Creek 1
Rocky Creek 2
Rocky Creek 3
Cliff
Point
SECOND CLUTCH
Culvert 1 and 2
OTHER STATES **
Michigan
Colorado
Total Nests
214
44
36
46
48
40
39
38
97
Total Eggs
755
147
109
167
182
150
138
133
326
Average Clutch Size
3.53
3.3^
3.11
3.63
3.81
3.75
3.5^
3.50
3.36
** Data supplied by North American Nest Record Card
Program.
29
TABLE 4. Number of eggs per nest. Data pooled for
all study colonies.
Eggs Per Nest
Number of Nests
9
17
73
129
2
230
% of Total
3.9
7.^
31.7
56.1
0.8
100.0
1
2
3
4
5
TOTAL
30
from clutches of 3, 89 per cent; from clutches of 2,
63 per cent. A high percentage (60.9^) of nests with
clutch sizes of 2 or less were abandoned. Only 10.2^ of
nests with 3 or more eggs were abandoned. In 1971,
hatching success in the two Rocky Creek colonies was
extremely, low. In 95 cliff swallow nests, a total of
252 eggs was laid of which 59.5 per cent never hatched.
Reasons for hatching failure of 44 eggs were undeter
mined or were due to storm destruction of nests. The
other 106 eggs contained embryos and had been abandoned.
The sequence of hatching was determined by oviposi-
tion sequence. The first egg laid hatched up to 72 hours
before the last egg. The first and second egg laid
hatched within the first 24-hour period; the third and
fourth egg laid hatched within a second 48-hour period.
The effects of ectoparasite concentrations upon
clutch size and hatching success were not determined.
Chemical control of ectoparasites was not initiated
until after hatching had begun in order to minimize the
chances of nest or colony abandonment due to human
disturbance.
Nestling Growth
Fledging Period and Success
The period from hatching until leaving the nest
averaged 25.3 days for 82 cliff swallow broods in
31
sprayed colonies. The fledging period was shorter
(23.2 days) for IO6 broods in parasitized colonies.
Fledging success, the percentage of hatchlings to
successfully leave the nest, was calculated for each of
the Justiceburg colonies (TABLE 5). The lowest fledging
success was experienced by the 2 Rocky Creek colonies
during 1971- Although no data were collected, these
colonies may have experienced much higher ectoparasite
densities, especially Oeciacus vicarius. than any
other colonies studied. A Chi-square test of independ
ence was employed to compare the percentage of nest
lings successfully fledging from unsprayed versus sprayed 2
colonies. The X of 14.18 shows that a significantly
(P< 0.001) higher level of success occurred in the
unsprayed colonies.
Weight
At the time of hatching or within 6 hours there
after, the weights of young cliff swallows varied
from 1.8 to 2.1 gm (Y=1.9, n=186, sd=0.71). Nestlings
showed an early, rapid growth phase which reached a
maximum on about the twelfth day after hatching (FIG. 5).
After a peak was achieved, a gradual loss of weight
occurred until fledging.
Nestlings exposed to ectoparasites did not achieve
as high a maximum weight as birds from treated colonies.
32
TABLE 5" Per cent fledging success in the study colonies,
Colony
NATURAL
Point
RC-1
RC-2
RC-3
Culvert 1
SPRAYED
Cliff
Culvert 2
Number Of
Nestlings
338
88
61
5^
76
59
252
167
85
Number That
Fledged
182
59
15
8
53
^7
236
160
76
Per cent Fledging Success
53.85 **
67.04
24.59
14.82
69.73
79.66
89.47 **
89.55
89.41
** X^ = 14.18 (P< 0.001) 1 df.
33
natural colonies. .
T;;ags^.t«^^
3^
"oT
.•o
.o CM
. "O o
T3
O
<
. o
Mi < > « < 3 a. <
• l O
"oT 01 —r-9
(UJ6) * H 6 ! » M
35
(TABLE 6). Disparity in weight was evident throughout,
the brooding period. Ectoparasitized young fledged
lighter than parasite-free nestlings. Due to the
small sample sizes from day 24 to fledging, day 23 of
nestling age was chosen for a statistical comparison of
nestling body weight near the fledging period. The
weight at day 23 of nestlings in sprayed and natural
colonies was compared using a single classification
analysis of variance. The resultant F value of 14.6
was highly significant (P< 0.001).
Weight growth curves were plotted for nestlings
on the basis of individual position in the hatch
sequence of each nest (FIG. 6). The first young that
hatched in a nest maintained a developmental advantage
over its cohorts throughout the brooding period.
Correspondingly, the second nestling that hatched
weighed more than the third and fourth; the third was
heavier than the fourth.
Primaries 1 and £
The primaries became evident as minute rounded
points on the fourth day. The inner and outer primaries,
1 and 9 respectively, had almost the same growth rates,
approximately 2.8 mm per day, until day 13. At that time
the growth rate of the outer primary increased to
about 3.7 mm per day; the inner primary growth rate
36
0 ^
H
•p RS -C - P
x; c •H tH
03 > - P
•H Q)
•H
0) P< O
O -PPL,
C - P o d to
• H ; a P4
O H O O
O
^ H O J
-P
O
o
vo
C •H
-o CD
H tH
•P
cd
T J
o 03
03 • H
<D O c (1) u (0
<H •H Q
03
H i
EH
IJM
Q
OH
03
l>H
EH
H
00
O ^ CsJ
vo
CM
VO
CM
CVJ
CVI
•H
00
H CM
0 ^ H
C ^ CVI
H
CVI
00 vo
H H H
H VO
cn
ON H
0 ^ 00
O CVJ
H H
«
H
CM
c^ CM
>> a Q
W) d
•H M
TJ Q)
H P4
l)!
FIGURE 6. Weight growth curve for nestlings based on hatch sequence. Data were pooled from the sprayed colonies. Time of hatch is plotted as day 1 to facilitate weight comparisons at common ages. Weights at days 11-23 are shown; prior to
day 11 overlap of individual weights prevented graphic clarity.
38
CM CM
. o.
- • O
o •D
« 0) <
o CO
—p-CM
—r-o CN
(u i6 ) •HBI9M
39
decreased to 1.2 ram per day.
When mean daily growth increments for primary 1
were compared, consistent and increasing differences
were noted between birds from natural and sprayed
colonies. The length of the inner primary at day 23
in the natural and sprayed (TABLE 7) colonies was
subjected to a single classification analysis of
variance. There was a significant difference (P< 0.001)
in fledging length of primary 1 between the treated and
natural colonies. A similar comparison of primary 9
daily lengths in natural and ectoparasite controlled
colonies revealed consistent differences in the means.
When compared at day 23 (TABLE 7) with a single class
ification analysis of variance, the lengths at fledging
were significantly different beyond P<0.001.
Most of the nestlings in the treated colonies
remained in the nest longer before they fledged. There
fore, their primary feathers had 1 to 2 days of extra
growth before they began to fly. When the additional
growth was considered, the inner primary was an average
of 7.0 mm longer at fledging in sprayed than in ecto
parasitized colonies and the outer primary was 4.1 mm
longer in treated colonies.
Rectrices
Both the inner and outer rectrices were measured.
However, due to the similarity of growth rates between
40
M x: +> bD
CD «H H O
© <»> OCVJ
•H lU >i •P Cd O 73 o ^^-p
cd
d 03 0)
• H
h^ U O CJH E o
•H O ^ PfTJ
0
d
bD
H
o
CD H >5-P d 03
C P O 03 03
•H -CJ
cd erf Pi E H o nJ
<U-P d
pq
•H
0) O
c (U tH tH •H P
03
EH
a.
liH
03
l>H
K
H
CM
00
00
H
00 VO CM
00 CO
CM CO
VO to C3N (O
H
H
O CM
VO CK
CO vr\ (vj
O ^
-:*• CM
s e ^
EH f^ ^ E
>i
u d E
•H U
PH
C3\
U d E
•H
0) o
•H u -p o
«
41
the 2 feathers, only the outer rectrice, rectrice 5,
was utilized for statistical analysis.
The outer rectrice appeared as a small dark knob
on the fourth day of nestling development. Growth
of the feather was slow until day 7 when it attained
a length of 1 mm. From day 7, the growth rate was
2.5 mm per day in the treated colonies and .2.4 mm per
day in ectoparasitized colonies. A 3.6 mm difference
in mean length at fledging was noted between ectopara
sitized and treated colonies. A single classification
analysis of variance revealed a significant difference
(P< 0.001) between the lengths at day 23 (TABLE 7) in
the 2 types of colonies.
Primary Coverts
Primary coverts 2 and 8 appeared as black spots
on the wing surface on the fifth day of nestling
growth. On day 8 they reached a length of 1 mm. The
growth of the coverts varied greatly within each
colony. The growth rate also varied daily. Growth of
the coverts was essentially completed on day 18, approx
imately 6 days prior to fledging. No statistical
difference was noted in the growth of the coverts
between treated and untreated colonies.
Tarsus and Ulna
Bone development of cliff swallows was difficult to
assess in living nestlings. Only 2 bones, the tarsus
42
and ulna could successfully be measured externally. The
measurements cited were slightly in excess of the actual
measurements because of the intervention of the skin
and a small amount of other tissue between the ends of
the bones and the scale.
The average tarsal length was 3.1 mm (n=98) on
the day of hatching. The growth rate of the tarsus
showed great variation within each colony. On the
fifth day of nestling growth, the mean tarsal length
in control colonies was 7.8 mm (range 7-9 mm); the
length in ectoparasitized colonies was 7.6 mm (range
7-10 mm). The maximum tarsus length of 11 mm was
attained on day 11 or 12 and did not increase beyond
that point. Until day 12 mean tarsal lengths were
consistently lower in ectoparasitized colonies. How
ever, the differences were not statistically significant.
Length at fledging was equal in both types of colonies.
For 26 nestlings measured within 8 hours after
hatching, the average ulna length was 5-0 mm. The
growth rate of the ulna also varied. A maximum length
of 26.1 mm was reached on day 20. No difference was
noted between the growth rate of the ulna in treated
and untreated colonies.
Blood Studies
Because of the hematophagous habits of the cliff
43
swallow ectoparasites, the blood of nestlings from
ectoparasitized colonies was compared to that of sprayed
colonies to determine if quantitative differences
occurred in the concentration of hemoglobin, hematocrit
and cellular elements.
The concentration of hemoglobin in the blood of
nestling cliff swallows, expressed as gm Hb per 100
ml blood, averaged 10.8 for 4o nestlings in colonies
exposed to ectoparasites. The mean value of hemoglo
bin concentration of 46 young in sprayed colonies was
14.6. Hemoglobin concentrations were subjected to a
single classification analysis of variance. A highly
significant difference (P< 0.005) was obtained indi
cating that ectoparasites lowered hemoglobin concentra
tions in parasitized nestlings.
The effect of nest ectoparasites on the blood
of nestling cliff swallows was also demonstrated by
a comparison of hematocrits. The mean per cent hema
tocrit was 51.5 for 77 nestlings in sprayed colonies
versus 47.3 for 67 young in ectoparasitized colonies.
When subjected to a single classification analysis
of variance, a highly significant difference (P< 0.005)
was obtained between sprayed and unsprayed colonies.
A gradual increase in hematocrit values with age
was noted during the study. The increase was most
44
obvious toward the end of the brooding period. A
two-way analysis of variance with replication was
utilized to compare the influence of ectoparasites
on hematocrit in 16 day-old and 21 day-old nestlings.
The difference in hematocrit due to age was highly
significant (P< 0.001). Significant differences in
hematocrit were also associated with ectoparasite
levels in the colonies (P< 0.025). The age, or stage
of development, interacts (P<0.25) with ectoparasite
density. The hematocrit of nestling cliff swallows
increased with age but was suppressed by ectoparasite
density within the colony.
A total of 156 dried blood smears were read and 2
the number of each cell type per mm in sprayed
and natural colonies was calculated (TABLE 8). Nest
lings from the sprayed colonies characteristically
possessed more erythrocytes and fewer of each type
of leukocyte than their counterparts from ectopara
sitized colonies. When compared with a Chi-square
test of independence, highly significant differences
(P<0.005) were obtained in the number of erythrocytes,
total leukocytes and lymphocytes in the two types of
colonies. The peripheral blood of the nestlings
also exhibited significant differences (P< 0.05) in
the total number of eosinophils and basophils.
^5
TABLE 8. A comparison of the cellular elements of the •J
blood per mm in natural and sprayed colonies.
Cell Type
Erythrocytes
Leukocytes (Total)
Lymphocytes
Monocytes
Thrombocytes
Polymorphonuclear Leukocytes (Total)
Heterophil
Eosinophil
Basophil
Sample Size
* P<0.05
** P< 0.005
Cells
Sprayed
11697
324
105
104
46
68
33
7
19
67
2 per mm
Natural
10602
516
213
135
62
106
50
28
5
91
x2
26.88 **
21.96 **
18.29 **
1.91 n.s.
1.17 n.s.
4.15 *
1.76 n.s.
5.83 *
4.03 *
46
Nestling Behavior
For the first 6 to 8 hours after hatching, nest
ling cliff swallows were essentially akinetic. The
few movements that occurred were performed slowly and
did not appear to be coordinated. Feeding during the
first 24 hours after hatching was accomplished largely
by parental force. Gaping, as a coordinated response,
began to develop during the second day of extra-embryonic
development.
From day 2 until day 8, gaping occurred whenever
the light intensity entering the nest was abruptly
changed. For example, positive gaping responses were
observed when either a flashlight beam brightened the
nest chamber or the nest was darkened by partially
obstructing the entrance.
Eye opening began on day 7 and was complete by
day 9- Visual stimulation of gaping began during
that period. By day 10, nestlings could distinguish
the form of a swallow from a foreign object. Crouch
ing and avoidance responses became common during this
period whenever foreign objects such as finger,
mirror or flashlight penetrated the nest entrance.
"Fear" responses were characterized by a crouch with
the head lowered in the deepest recesses of the nest.
Young cliff swallows defecated in the nest until
7
the eyes opened and vision developed. Parent cliff
swallows removed the fecal deposits and dropped
them in flight 10 to 20 meters away. Parental effi
ciency at pellet removal began to decline on about
the sixth day of brood development. On the tenth day,
the nestling cliff swallows attempted to back up to
the nest entrance and defecate. Accidents, at the
nest entrance, due to either lack of coordination
or cohort pressure, greatly increased mortality during
this period.
A cohort hierarchy was evident in the arrangement
of nestlings about the entrance. The order at the
nest opening was related to physical development and
size. The 2 oldest and, hence, largest young of a brood
dominated the nest entrance. Much of the food brought
to the nest by the parents was taken by these birds.
The other members of a brood received food only
sporatically. This contributed to the lowered weight
gain rates of late hatching nestlings. The orientation
of early-hatched young about the entrance also may have
contributed to the higher mortality rates for nestlings
3 and 4. The pressure of the dominant young probably
increased defecation-related accidental falls in
subordinate brood members.
48
Mortality Factors
Behavioral Mortality
Records were kept and a graph was prepared to
show the pattern of disappearance of young swallows
from the nest. An upward inflection occurred during
the period (days 9-11) when extra-nest fecal deposi
tion was first being attempted (FIG. 7). A second
inflection occurred during days 17-20 when gaping
at the nest entrance was begun. Although behavioral
mortality was not impressive in terms of overall
colony mortality, it did contribute to the total. The
loss of 2,S% of the nestlings in the study colonies
was attributed to behavior.
Bridge-situated colonies suffered vehicle-related
attrition. Adult cliff swallows would swarm from the
nests whenever danger calls were emmitted. This be
havior often occurred when a heavy truck or bus entered
the bridge. Swarming flights often carried the flock
over the highway and into the path of vehicles. Cliff
swallows were also observed feeding on traffic-killed
insects on the highway pavement. Red ant beds on the
shoulders of highways were ground-feeding sites
utilized by cliff swallows. These habits contributed
to traffic loss. Loss of one or both parents may
have lowered nest success percentages in some
49
FIGURE 7' Pattern of nestling disappearance from nests. Number of nestlings missing per 100 nests plotted against nestling age. Data were pooled for all
colonies.
50
1 2 6 8 10 12 14 16 18 20
Age (days)
51
colonies.
Nest Destruction
A total of 6 nests were accidentally destroyed by
me during the 2 years of study. As a result 18 young
were killed. Another 4 young died from mishandling.
To minimize losses, 1972 colony sites were visited for
investigative purposes only during that portion of
the day when they were shaded.
Natural disasters, such as violent rain storms,
may affect nesting success in some years. Most of the
colonies at Justiceburg were constructed imder over
hangs which offered protection from the direct effects
of rain. In addition, most of the colonies were sit
uated so that a prevailing wind current blew the rain
away from the nests. However, rivulets of water
washing down the cliff face did destroy some nests
during rain storms. Nests on the periphery of the
colony were more affected than were centrally located
nests. Peripheral nests were often constructed in
obvious routes of cliff watersheds. In 1971 the loss
of 44 eggs was attributed to the rainwash destruction
of 13 nests, all of which were peripherally located.
Nest Abandonment
In 1971 an entire section of the Rocky Creek-2
colony (100-200 nests) was abandoned. A study of 55
52
eggs taken from various nests in the abandoned colony
showed that 53 had embryos in late stages of develop
ment. No definite cause for the abandonment was
determined. However, the colony had been disturbed
the night before the abandonment by efforts to collect
ectoparasites. Several colonies had been visited on
that night and had been equally disrupted but this was
the only colony that was deserted. There was no
apparent reason why this particular colony was abandoned,
and the other disturbed colonies were not. Three paint-
marked birds from this colony were involved in nest
construction six days later at a colony 0.3 km distant.
Colony desertion occurred again in 1972. Approx
imately 25 pairs of cliff swallows began nest con
struction on the west side of the Double Mountain Fork
of the Brazos. On May 11, 8 of the nests were examined
and were found to contain full clutches. The site was
utilized by swallows until May 15, when it was aban
doned. A total of 24 eggs from 20 nests contained late
embryos.
In the latter stages of brood development, early
broods began to fledge as much as a week before the
late broods. During both years of the study, clutches
were laid in post-fledging nests while other nests in
the colony still contained broods. In some cases.
53
full clutches were laid and incubation was initiated.
However, when the last of the original brood had fledged,
the colony site and the new clutches were abandoned.
No evidence was obtained to ascertain whether the
abandoned clutches represented second brood attempts
by a pair of swallows that had already reared a clutch
at the colony.
Predation
Because of the relative inaccessability of cliff
swallow colonies, predation did not influence nest
success. Only one direct observation of predation
in the nest was witnessed. On 28 June 1972 a bull-
snake , Pituophis melanoleucus, was observed entering
nests and devouring young cliff swallows at a culvert
near Six Gun City, 8 miles E Canyon, Randall County,
Texas. It was conceivable that some of the disappear
ances of young birds or eggs might have been due to
predation by snakes. However, the lack of data voided
any conclusions in this regard.
Predation on adult birds was not witnessed. How
ever, a number of rattlesnakes was observed below the
colonies and at cliff swallow sunning sites. Cliff
swallows involved in copulation frequently fell
from the nest to the ground below the colonies where
they could be subject to predation. Sufficient
54
observational data were not obtained to quantitatively
assess predation loss.
Hatch Sequence Effects
As has already been demonstrated, hatching se
quence influenced the rate of weight gain in nestling
cliff swallows. A differential mortality rate related
to hatching sequence was also observed. When the per
cent mortality of nestlings was computed with respect
to hatching sequence (TABLE 9), a higher mortality
rate was noted for late hatching individuals in both
treated and natural colonies. Chi-square tests of
independence were employed to determine if there was
a significant difference in the mortality before •
fledging between nestlings of corresponding hatching
sequence. The differences in mortality between early
hatching young were not statistically significant.
However, highly significant differences were obtained
between mortality rates in late hatching cohort
members in both sprayed and untreated colonies.
It was noted that mortality tended to increase
among late hatching young in both colonies. To test
the trends RXC test of independence using the G-test
were employed. In the ectoparasitized colonies a
G-value of 11.98 was obtained. The G-value is signi
ficant at P-^0.01, and the null hypothesis that hatching
55
TABLE 9. Mortality according to hatch sequence in
ectoparasitized and sprayed colonies.
Hatch Mortality
Sequence Ectoparasitized Sprayed
1 5.21 4.11
2 8.79 5.^1
3 21.05 8.20
^ ^5.59 11.32
Chi-square test for independence (Ectoparasitized vs. sprayed)
,2 Hatch Sequence Comparisons 3
1 v s . 1 0.23 n . s .
2 v s . 2 1.29 n . s .
3 v s . 3 7.84 P< 0.01 (1 df)
4 v s . 4 25.76 P< 0.005 (1 df)
5S
sequence does not influence nestling mortality must
be rejected. In the control colonies a G-value of
0.751 was obtained which was not significant.
Total Mortality
Total mortality was calculated for each colony.
The data were grouped according to the treatment the
colonies received and were summarized in TABLE 10.
A 2X2 Chi-square test of independence was utilized to
compare mortality in natural versus sprayed colonies.
A highly significant difference (P< 0.005) was obtained
indicating that increased nestling mortality was
induced by the ectoparasites in unsprayed sites.
Therefore, productivity was adversely affected at
those sites.
A 2X2 Chi-square test of independence was also
employed to determine if brood production in the
Justiceburg area during the second half of the summer
could compensate for low productivity in the first
brood. A highly significant difference in mortality
(P< 0.005) was obtained between the broods which were
produced during the first and second portions of the
summer in unsprayed sites. The difference in mortality
between the Point, which had the lowest mortality
among untreated colonies (60 7? ) and culvert bent 1
(18.9?$) was evidence that the trend among the Justiceburg
51
TABLE 10. Total mortality in the natural and sprayed colonies. A 2X2 Chi-square test for independence
used to test for significance.
Colony
NATURAL
Point
RC-1
RC-2
RC-3
Culvert
SPRAYED
Cliff
Culvert
1
2
Number Of
Eggs
755
150
147
109
167
58
260
182
80
Number That Fledged
182
59
15
8
53
47
236
160
76
Total Mortality
75.9
60.7
89.8
92.7
68.3
. 18.9
9.2
12.1
5.0
Comparison
2X2 Chi-square Test Of Independence
2 X
Natural vs. Sprayed 76.69 **
** P <0.005 for 1 df
58
cliff swallows to use man-made structures for nesting
during the second part of the summer aided in compen
sating for high early summer mortality.
CHAPTER IV
DISCUSSION
From the time of hatching a complex of factors
influence the development and survival of nestling
cliff swallows. These elements include weather, food
availability, predation, pathogenic endoparasites and
ectoparasites. In this study, 1 of the factors, ecto
parasites, was controlled at certain colony sites to
determine the influence that hematophagous arthropods
exerted on the growth and fledging success of cliff
swallows.
. Complex social interactions (Darling 1938)
synchronize the selection of a nesting site and repro
ductive physiology among flocks of swallows. The in
crease in ectoparasite populations at nest sites may
further contribute to reproductive synchrony. Late
broods would be exposed to higher parasite densities,
throughout their development. Nestling survival is thus
lowered in late broods. Swallow aggregations that
exhibit synchrony have a selective advantage in terms
of brood production.
The size of cliff swallow clutches varies from
1 to 5 eggs (Storer 1927, Bent 19^2, Samuel 1971).
Myers (1928) found that early clutches contained a
59
60
larger number of eggs (4 or 5), whereas later clutches
usually contained only 3 eggs. No difference was noted
in this study between average clutch sizes in broods
produced during different portions of the summer.
There is some dispute concerning renesting and
second brood rearing in cliff swallows. Most obser
vers agree that cliff swallows raise 2 broods of young
during any 1 breeding season (Bent 1942). No band data
are available to support this contention but it seems
likely that 2 broods were produced at Justiceburg. There
were 2 definite periods of brood rearing by the cliff
swallows in the area. Fledging and colony abandonment
of the early summer brood was followed within the week
by nest site selection and subsequent brood rearing
during the second half of the summer. The temporal
coordination between first brood fledging and the
initiation of a second reproductive cycle could hardly
be due to chance. Therefore, the second brood produced
in the area was probably reared by some of the same
adults that produced the first.
That incubation began before the clutch was com
pleted was evident from the variation of developmental
stages found within individual nest cohorts. Defini
tive evidence was provided by egg marking experiments
which demonstrated that the eggs hatched in the same
61
order as laying. Intermittent incubation prior to
clutch completion has been documented for several
species of swallows (Peterson 1955, Samuel 1971).
From the time of hatching the impact of ecto
parasites could clearly be demonstrated in the develop
ment of nestling cliff swallows. The irritation of
the ticks and swallow bugs undoubtedly contributed
to the shortened fledging period seen in untreated
colonies. Similar early fledging accompanying large
populations of the mite, Ornithonyssus silvarium,
caused significant mortality in phoebes (Klaas, In
Moss and Camin 1970). The survival potential of pre
maturely fledged young is lower than those that remain
in the nest until maximum development is achieved
(Royama 1966).
The weight growth curve for nestling cliff swallows
was similar to that reported by Stoner (1945). Weight
recession prior to fledging is characteristic of swallows,
swifts and oceanic species. It is related to reduction
in the proportion of body water in preparation for
flight (Ricklefs I968). Differences in daily weights
of nestlings between the treated and untreated colonies
were good indicators of ectoparasite influence. A
positive relation between maximum nestling weight and
survival after fledging seemed likely in cliff swallows,
although I lack evidence to support this contention.
62
However, a high correlation between fledging weight
and subsequent survival has been demonstrated in other
birds (Perrins I965, Moss and Camin I970).
Daily measurements of the inner and outer pri
maries and rectrices also reflected the influence of
ectoparasites. The lengths of the flight feathers
were consistently lower in the nestlings from unsprayed
colonies. This was regarded as evidence that blood
loss due to ectoparasites produced an energy drain on
the young swallows. Energy that was normally devoted
to feather growth was presumably channeled into blood
maintenance and infection inhibition. If so, nestlings
from parasitized colonies may have been less prepared
for flight when they fledged and may have had a lower
chance for survival.
The disparity in hatching sequence among a brood
cohort resulted in a behavioral and developmental lag
among the late hatching nestlings.. Early hatched
young tended to dominate the nest entrance and prob
ably obtained more food than their younger nest mates.
This increased the weight difference within a brood.
Developmental differences among a nest cohort resulted
in a slight trend toward higher mortality among late
hatched nestlings in sprayed colonies but the trend
was not statistically significant. However, the
63
mortality increments were statistically significant
in ectoparasitized colonies. These differences were
attributed to the presence of the ticks and swallow
bugs. Apparently, nestlings of lowered weight were
in general weaker and they were affected to a greater
degree by blood loss than were the early hatched,
heavier young in a nest. This effect is accentuated
by the fact that late-hatched nestlings are in the
nest longer, and thus exposed to higher ectoparasite
concentrations during the latter stages of brooding
than are early-hatched young.
That heavy infections of hematophagous arthropods
may seriously weaken or kill avian hosts has been
noted by several authors (Herman 1937, Putzig 1939,
Boyd 1951). Such ectoparasites may induce weight loss,
edema, hyperemia or introduce bacterial infections
(Jellison and Kohls 1938, Smith and Cheatum 1944) although
Baerg (19^^) was unable to recognize any of the above
symptoms in nestling cliff swallows. However,_ anemia was
consistently prevalent among the ectoparasitized nest
lings at the Justiceburg site. The significant differ
ences in hemoglobin concentration, hematocrit and
erythrocyte counts were the most direct measurement of
the influence of the hematophagous ectoparasites.
Leukocytosis, which may indicate bacterial infections,
was common among the nestlings in natural colonies.
64
Significant increases of lymphocytes and polymorphonuclear
leukocytes in the blood of parasitized nestlings indi
cate tissue inflammation and infection (Lucas and
Jamroz I96I). Heterophils may increase with parasitic
infestations and are found in the tissues in certain
allergic states (Olson I965). Infections and severe
anemia may have resulted in nestling mortality in the
untreated colonies.
All other factors being approximately equal,
total mortality was the greatest among nestlings in
ectoparasitized colonies. Thus, normal concentra
tions of ticks and swallow bugs have an appreciable
effect on lessening the productivity among cliff,
swallow broods.
Alternate nest site usage patterns may have evolved'
as a result of population increases of endemic ecto
parasites. Annual utilization of the same site would
be advantageous from the standpoint of nest construc
tion, but continual site habitation would allow the
ectoparasite population to increase to the point where
the parasites might cause total or excessive brood
mortality. Moss and Camin (1970) demonstrated that
annual usage of purple martin colonies increased
ectoparasite induced mortality. Populations of cliff
swallows which developed alternate site habituation
patterns had a selective advantage over swallow pop-
65
ulations that did not alternate site selections.
Similarly, the evolution of second brood rearing
in cliff swallows may have been concurrent with
ectoparasite-reduced productivity in initial broods.
Populations that suffered heavy first brood mortality
and then renested within the same season would have a
selective advantage if they utilized a different site.
Populations that did not renest probably dwindled away.
Below a certain minimum population size, social facilita
tion in cliff swallows seems to cease and reproduction
may fail (Emlen 1952).
CHAPTER V
SUMMARY
This study has shown that the level of the ecto
parasite infestations at unsprayed cliff swallow col
onies steadily increased throughout the brooding period.
Chemical control of the ticks and swallow bugs at 2
sites provided a basis for comparison of the effects
of the parasites on the development and mortality of
nestling swallows at untreated sites. The ectoparasites
significantly reduced nestling weight and flight
feather growth. The effects of the hematophagous habits
of the ectoparasites was demonstrated in lowered
hematocrit, hemoglobin concentration and erythrocyte
counts of the nestlings' blood. Leukocytosis was
evidence of tissue inflammation and bacterial infection.
Nestling mortality was significantly higher in ecto
parasitized colonies. Nestlings which hatched late
in a brood suffered higher mortality rates than their
early-hatched cohorts. It was hypothesized that alter
nate nest site usage patterns and second-brood rearing
have evolved in cliff swallow populations to compensate
for ectoparasite-induced mortality.
66
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