Complete Sanitation of Dead Nestlings by Parent Birds May Bias Nest Complete Sanitation of Dead Nestlings by Parent Birds May Bias Nest Depredation Rates Depredation Rates

Chris KirkpatrickChris Kirkpatrick11, Courtney J. Conway, Courtney J. Conway22, and Moez H. Ali, and Moez H. Ali11

1 1 University of Arizona; University of Arizona; 2 2 USGS Arizona Cooperative Fish and Wildlife Research UnitUSGS Arizona Cooperative Fish and Wildlife Research Unit

ABSTRACTABSTRACT

EstimatesEstimates of avian nesting success typically assume that nests of avian nesting success typically assume that nests found to be empty and intact (i.e., nest cup and lining found to be empty and intact (i.e., nest cup and lining undisturbed; Fig. 1) prior to fledging are likely to have been undisturbed; Fig. 1) prior to fledging are likely to have been depredated. We provide evidence that an empty nest may not depredated. We provide evidence that an empty nest may not always indicate a depredated nest, but instead may result from always indicate a depredated nest, but instead may result from complete sanitation of dead nestlings by parent birds. In 2006, complete sanitation of dead nestlings by parent birds. In 2006, we used time-lapse video cameras to monitor nests of red-faced we used time-lapse video cameras to monitor nests of red-faced warblers (warblers (Cardellina rubrifronsCardellina rubrifrons; Fig. 2) and yellow-eyed juncos ; Fig. 2) and yellow-eyed juncos ((Junco phaeonotusJunco phaeonotus; Fig. 2) in high-elevation, mixed-conifer ; Fig. 2) in high-elevation, mixed-conifer forests of the Santa Catalina Mountains, Arizona. Following rain forests of the Santa Catalina Mountains, Arizona. Following rain and hail storms on 4 & 5 July 2006, video footage revealed that and hail storms on 4 & 5 July 2006, video footage revealed that parent yellow-eyed juncos and red-faced warblers removed all parent yellow-eyed juncos and red-faced warblers removed all nestlings from 2 nests (the nestlings apparently died after the nestlings from 2 nests (the nestlings apparently died after the storms). Our results indicate that complete sanitation of dead storms). Our results indicate that complete sanitation of dead nestlings by parent birds may be a relatively common behavior, nestlings by parent birds may be a relatively common behavior, suggesting that researchers use caution when assigning fates to suggesting that researchers use caution when assigning fates to empty nests during future nest-monitoring studies.empty nests during future nest-monitoring studies.

RESULTS (CONTINUED)RESULTS (CONTINUED)

• Daily nest survival (DNS) was lower for all RFWA and YEJU Daily nest survival (DNS) was lower for all RFWA and YEJU nests (nests (nn = 17) monitored during the 5-day period before the = 17) monitored during the 5-day period before the storms compared to the 5-day period after the storms.storms compared to the 5-day period after the storms.

DNS pre-storm = 1.0 (SE = 0)DNS pre-storm = 1.0 (SE = 0) ZZ = 1.8 = 1.8DNS post-storm = 0.938 (SE = 0.036)DNS post-storm = 0.938 (SE = 0.036) PP = 0.07 = 0.07

• Sixty-seven percent of nests that failed after the storms were Sixty-seven percent of nests that failed after the storms were incorrectly identified by field personnel as having been incorrectly identified by field personnel as having been depredated (video footage revealed these nests failed due to depredated (video footage revealed these nests failed due to weather and were later sanitized by parent birds).weather and were later sanitized by parent birds).

Figure 1. An empty, intact red-faced warbler nest - depredated or sanitized?Figure 1. An empty, intact red-faced warbler nest - depredated or sanitized?

STUDY AREASTUDY AREA

• 5 16-20 ha plots located in high-elevation (2,300-2,800 m), 5 16-20 ha plots located in high-elevation (2,300-2,800 m), mixed-conifer mixed-conifer forest of the Santa Catalina Mountains, Arizona.forest of the Santa Catalina Mountains, Arizona.

• Mean annual precipitation in the Santa Catalina Mountains is Mean annual precipitation in the Santa Catalina Mountains is 26.8 inches (Brown 1994) with most precipitation falling during 26.8 inches (Brown 1994) with most precipitation falling during a brief season of strong thunderstorms that begins in early July. a brief season of strong thunderstorms that begins in early July.

METHODSMETHODS

• FFrom rom April-JulyApril-July 2006, 2006, wwe me monitored a total of 148 red-faced onitored a total of 148 red-faced warbler and yellow-eyed junco nests warbler and yellow-eyed junco nests uusing standard nest-sing standard nest-monitoring protocols (Martin and Geupel 1993)monitoring protocols (Martin and Geupel 1993)..

• We uWe used time-lapse video cameras to continuously monitor a sed time-lapse video cameras to continuously monitor a subset of 18 nests during the incubation and nestling periods. subset of 18 nests during the incubation and nestling periods.

• We compared estimates of daily nest survival (Mayfield 1961, We compared estimates of daily nest survival (Mayfield 1961, 1975) during a 5-day period before and during a 5-day period 1975) during a 5-day period before and during a 5-day period after strong thunderstorms on 4 & 5 July 2006. after strong thunderstorms on 4 & 5 July 2006.

RESULTSRESULTS

• Two nests (1 RFWA and 1 YEJU) that were monitored continuously by video cameras and checked Two nests (1 RFWA and 1 YEJU) that were monitored continuously by video cameras and checked periodically by field personnel failed in early July 2006 (Table 1). periodically by field personnel failed in early July 2006 (Table 1).

• Both nests contained young nestlings (1-4 days old) prior to failure.Both nests contained young nestlings (1-4 days old) prior to failure.

• Field observers assumed that the RFWA nest had been depredated (the nest was empty and intact) and the Field observers assumed that the RFWA nest had been depredated (the nest was empty and intact) and the YEJU nest had been partially depredated (the nest had 1 infertile egg and was intact).YEJU nest had been partially depredated (the nest had 1 infertile egg and was intact).

• Video footage showed parent birds sanitizing nests by removing the entire brood of dead nestlings (Fig. 3).Video footage showed parent birds sanitizing nests by removing the entire brood of dead nestlings (Fig. 3).

• Precipitation and temperature data from 2 local weather stations (Figs. 4 & 5; Pima County 2006) indicated Precipitation and temperature data from 2 local weather stations (Figs. 4 & 5; Pima County 2006) indicated that strong storms occurred on 4 & 5 July 2006, 1-2 days before the failure of both nests.that strong storms occurred on 4 & 5 July 2006, 1-2 days before the failure of both nests.

ACKNOWLEDGMENTS ACKNOWLEDGMENTS

We thank M. Eastwood, N. Nardello, and T. Selvidge for assistance locating nests and operating video We thank M. Eastwood, N. Nardello, and T. Selvidge for assistance locating nests and operating video cameras and S. Sferra (Bureau of Reclamation) for the loan of the video cameras. Funding was cameras and S. Sferra (Bureau of Reclamation) for the loan of the video cameras. Funding was provided by the U.S. Fish and Wildlife Service and the U.S. Geological Survey.provided by the U.S. Fish and Wildlife Service and the U.S. Geological Survey.

LITERATURE CITEDLITERATURE CITED

Brown, D. E. 1994. Biotic Communities Southwestern United States and Northwestern Mexico. Brown, D. E. 1994. Biotic Communities Southwestern United States and Northwestern Mexico. University of Utah Press, Salt Lake City, Utah.University of Utah Press, Salt Lake City, Utah.

Dunn, E. H. 1976. The relationship between brood size and effective homeothermy in nestling house Dunn, E. H. 1976. The relationship between brood size and effective homeothermy in nestling house wrens. Wilson Bull. 88:478-482.wrens. Wilson Bull. 88:478-482.

Martin, T. E., and G. R. Geupel. 1993. Nest-monitoring plots: methods for locating nests and Martin, T. E., and G. R. Geupel. 1993. Nest-monitoring plots: methods for locating nests and monitoring success. Journal of Field Ornithology 64:507-519.monitoring success. Journal of Field Ornithology 64:507-519.

Mayfield, H. 1961. Nesting success calculated from exposure. Wilson Bull. 73:255-261.Mayfield, H. 1961. Nesting success calculated from exposure. Wilson Bull. 73:255-261.Mayfield, H. 1975. Suggestions for calculating nest success. Wilson Bull. 87:456-466.Mayfield, H. 1975. Suggestions for calculating nest success. Wilson Bull. 87:456-466.Pima County. 2006. Pima County. 2006. Pima County ALERT System. http://rfcd.pima.gov/alertsys/Pima County ALERT System. http://rfcd.pima.gov/alertsys/Stewart, R. M. 1972. Nestling mortality in swallows due to inclement weather. Ca. Birds 3:69-70.Stewart, R. M. 1972. Nestling mortality in swallows due to inclement weather. Ca. Birds 3:69-70.

Bruce TaubertBruce Taubert Bruce TaubertBruce Taubert

Figure 2. Yellow-eyed junco (YEJU; left) and red-faced warbler (RFWA; right) - 2 ground-nesting birds that breed in close association in southeastern AZ.Figure 2. Yellow-eyed junco (YEJU; left) and red-faced warbler (RFWA; right) - 2 ground-nesting birds that breed in close association in southeastern AZ.

Figure 4. Daily precipitation recorded from 10 June to 12 July 2006Figure 4. Daily precipitation recorded from 10 June to 12 July 2006 at at Mt. Lemmon and Marshall Gulch weather stations, Santa Catalina Mt. Lemmon and Marshall Gulch weather stations, Santa Catalina Mountains, AZ (Pima County 2006). Stations were located <1 km from Mountains, AZ (Pima County 2006). Stations were located <1 km from study plots.study plots.

RFWA nest sanitized

YEJU nest sanitized

Table 1. Characteristics of failed red-faced warbler (RFWA) and Table 1. Characteristics of failed red-faced warbler (RFWA) and yellow-eyed junco (YEJU) nests in Santa Catalina Mountains, AZ.yellow-eyed junco (YEJU) nests in Santa Catalina Mountains, AZ.

RFWARFWANestNest

YEJUYEJUNestNest

Elevation (m)Elevation (m) 2,3002,300 2,7772,777

Initiation DateInitiation Date 6/186/18 6/206/20

Clutch SizeClutch Size 33 33

Number of NestlingsNumber of Nestlings 33 22

Date of Nest FailureDate of Nest Failure 7/57/5 7/47/4

Date Nest Sanitized by AdultsDate Nest Sanitized by Adults 7/67/6 7/57/5

Nestling Age (in Days) at FailureNestling Age (in Days) at Failure 44 11

Figure 5. Temperature and precipitation recorded on 4 July 2006Figure 5. Temperature and precipitation recorded on 4 July 2006 at the at the Mt. Lemmon weather station, Santa Catalina Mountains, AZ (Pima Mt. Lemmon weather station, Santa Catalina Mountains, AZ (Pima County 2006). The first storm began at approximately 1230.County 2006). The first storm began at approximately 1230.

Figure 3. Still image from video footage showing female Figure 3. Still image from video footage showing female yellow-eyed junco removing dead nestling from nest on yellow-eyed junco removing dead nestling from nest on 5 July 2006 in the Santa Catalina Mountains, AZ5 July 2006 in the Santa Catalina Mountains, AZ

DISCUSSIONDISCUSSION

• We provide evidence that an empty, intact nest may not always We provide evidence that an empty, intact nest may not always indicate a nest depredation, but instead may result from indicate a nest depredation, but instead may result from complete sanitation of dead nestlings by parent birds following complete sanitation of dead nestlings by parent birds following inclement weather. inclement weather.

• Inclement weather can lead to complete brood mortality Inclement weather can lead to complete brood mortality (Stewart 1972) (Stewart 1972) and young (1-8 day old) nestlings are especially and young (1-8 day old) nestlings are especially susceptible because of their inability to maintain constant body susceptible because of their inability to maintain constant body temperature (Dunn 1976).temperature (Dunn 1976).

• Preliminary results suggest that complete sanitation of dead Preliminary results suggest that complete sanitation of dead nestlings by parent birds may be a relatively common behavior nestlings by parent birds may be a relatively common behavior in red-faced warblers and yellow-eyed juncos.in red-faced warblers and yellow-eyed juncos.

• The frequency with which this behavior may occur in other The frequency with which this behavior may occur in other species is unknown. However, complete brood mortality and species is unknown. However, complete brood mortality and subsequent sanitation of dead nestlings is likely to occur:subsequent sanitation of dead nestlings is likely to occur:

1) following strong storms1) following strong storms2) at nests that are prone to flooding2) at nests that are prone to flooding3) when nestlings are young and brood sizes 3) when nestlings are young and brood sizes are small (Dunn 1976)are small (Dunn 1976)

• Researchers should use caution when assigning fates to empty, Researchers should use caution when assigning fates to empty, intact nests (especially after inclement weather) given that the intact nests (especially after inclement weather) given that the incorrect assignment of nests fates has the potential to bias nest incorrect assignment of nests fates has the potential to bias nest depredation rates.depredation rates.