1. Predation and the use of Tamarisk as a nesting substrate by Southwestern Willow Flycatchers (Empidonax traillii extimus) Stephanie Muise, Katie Stumpf Natural 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. 1.Explore predation of Southwestern Willow Flycatcher nests along the Middle Rio Grande river corridor at two scales: 1. 1.Nest substrate (tree species nest was built in) 2. 2.Territory (dominant vegetation within 20 m) 2. 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. 1.Tree species the nest was built in (substrate; native/non-native) 2. 2.Dominant vegetation within 20m (Dominant Territory Vegetation; native/mixed/non-native) BACKGROUNDMETHODS 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. 1.At the substrate and territory scales, nests in non-native are less often predated. 2. 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 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 Predated % Predated, Native DTV % Predated, Non-Native DTV Belen (N/NN)348240 Tiffany (N/Mix)44214867 Sevilleta (Mix)10042 54 SanAcacia (Mix)62330 Bosque (N)134604530 Escondita (N)4591713750 SanMarcial (N)122945037 Narrows (N)1466746 * * *