Predation and the use of Tamarisk as a nesting substrate by Southwestern Willow Flycatchers (Empidonax traillii extimus)

Stephanie Muise, Katie StumpfNatural Resources Department, Northland College, Ashland WI

• Predation and parasitism are the main causes of nest failure for all songbirds and negatively impact nesting success and subsequent population size (Martin 1992)

• Southwestern Willow Flycatchers are a federally endangered riparian neotropical migrant (USFWS 1995) which historically nest in native willows (Salix spp.), but are increasingly found nesting in non-native Tamarisk (Tamarix spp.).

• Tamarisk root systems drain down water columns and out compete native willows for resources in riparian zones, resulting in long-term structural changes to riparian habitats in the southwestern US which may lead to an increase in predation risk on songbird nests (Di Tomaso, J.D, 1998, Morrisette et al. 2006)

• Southwestern Willow Flycatcher nests in Tamarisk may be less productive than those in native vegetation, however, few studies have examined predation in native versus non-native habitat types.

Research Objectives:1. Explore predation of Southwestern Willow Flycatcher nests along the

Middle Rio Grande river corridor at two scales:1. Nest substrate (tree species nest was built in)2. Territory (dominant vegetation within 20 m)

2. Recommend actions and propose future research directions for the population recovery of Southwestern Willow Flycatchers.

• We conducted surveys along the Middle Rio Grande river in New

Mexico between the Isletta Pueblo reservation and Elephant Butte

Reservoir (Figure 1, Figure 2)• We surveyed each site 4-5 times between May and August 1998-2004

using standard callback survey techniques • We observed nests every 2-4 days using mirror-poles (Figure 3),

recording:• Nesting status (predated, abandoned, parasitized or fledged)• Number of nestlings and estimated age

• We recorded habitat at two scales:

1. Tree species the nest was built in (substrate; native/non-native)

2. Dominant vegetation within 20m (Dominant Territory Vegetation;

native/mixed/non-native)

BACKGROUND

METHODS

1. Substrate Scale• Nests built within non-native vegetation are less often depredated than those nests that are built within native

vegetation (Figure 4)

2. Dominant Territory Vegetation Scale• Nests built within non-native territories are less often depredated than those nests that are built within mixed

territories or native territories. (Figure 5)• Nests built in territories with mixed habitat have an intermediate level of predation in comparison to predation in

native dominated territories and non-native dominated territories (Figure 5).• However, when we pooled data by site, at three of six sites with complete vegetation profiles, nests built in

territories with non-native habitat are more often depredated than those built in those with mixed or native

territories. (Figure 6, Table 1)

Figure 5: Percent predated nests by dominant territory vegetation class.

Figure 4: Percent predated nests by substrate class

RESULTS

Di Tomaso, J.D., 1998, Impact, Biology and Ecology of Salt Cedar (Tamarisk spp.) in the Southwestern United States, Weed Technology, Vol 12, No. 2, pp 326-336

Martin. Nest Predation and Nest Sites. BioScience (1993) vol. 43 (8) pp. 523-532

Morrisette, J.T. et al., 2006, A Tamarisk Habitat Suitability Map for the Continental United States, Frontiers in Ecology and the Environment, Vol.4, No.1, pp. 11-17

Sogge, M.K. et al., 2010, A Natural History Summary and Survey Protocol for the Southwestern Willow Flycatcher; U.S. Geological Survey Techniques and Methods 2A-10, 38

United States Fish and Wildlife Service, 1995, Final Rule Determining Endangered Status for Southwestern Willow Flycatchers, U.S. Federal Register 60:10694-10715

This research has been supported by the following organizations and

individuals. • Bureau of Reclamation (Albuquerque office and the field crews)• Advisors and staff at Northland College

When put into context of modern conservation efforts within the middle

Rio Grande, the main focus has been to remove Tamarisk to improve

reproductive success of the Southwestern Willow Flycatcher. However,

given our results, it reproductive success may not always follow this

costly management action and may depend on the scale of the study.

1. At the substrate and territory scales, nests in non-native are less often

predated.

2. At the landscape/site scale, nests built in native dominated territories

are less often successful.

This difference in reproductive success at the different scales may be

because of changes that habitat fragmentation caused by mass Tamarisk

removal (Figure 7) have on predator communities.

Potential Implications:• Managers should consider minimizing the removal of Tamarisk by

heavy equipment or anthropogenic disturbance that fragments habitat

and alters predator communities.• Asses management goals to factor in reproductive success and habitat

changes at various scales. • Continue monitoring efforts to better understand predator

communities differences across vegetation types within the middle

Rio Grande corridor.• Analyse the potential of integrating Tamarisk as a management tool

for the recovery of the Southwestern Willow Flycatcher.

CONCLUSIONS

ACKNOWLEDGEMENTS

REFERENCES

Native Mixed Non-native0

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Native Non-Native-1.11022302462516E-16

0.0999999999999999

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Belen (N/NN) Sevilleta (Mix) Bosque (N) SanAcacia (Mix) Escondita (N) Tiffany (N/Mix) SanMarcial (N) Narrows (N)0.00

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% Predated, Native DTV % Predated, Mix DTV % Predated, NN DTV

Reach (North to South)

Perc

ent

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date

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Figure 6: Percent predated nests by landscape vegetation. Letters in parenthesis indicate dominant vegetation throughout reach and asterisks

indicate sites where predation was higher in non-native territories.

Figure 3: Eggs viewed using a mirror-pole.

Figure 2: Example of willow dominated habitat, Middle Rio Grande River

Figure 7: Habitat after Tamarisk removal

Table 1. Total number of nests, number depredated, and percent predation by dominant territory vegetation, at each of eight sites along the Middle Rio.

Figure 1. Map of New Mexico and the Rio Grande River;

survey area outlined in red box.

Site Total Nests

Nests Predate

d

% Predated,

Native DTV

% Predated, Non-Native

DTV

Belen (N/NN) 34 8 24 0

Tiffany (N/Mix) 44 21 48 67

Sevilleta (Mix) 100 42 42 54

SanAcacia (Mix) 6 2 33 0

Bosque (N) 134 60 45 30

Escondita (N) 459 171 37 50

SanMarcial (N) 1229 450 37 37

Narrows (N) 146 67 46 46

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