The endangered willow flycatcher (Empidonax traillii) breeds in mountain meadows in the Sierra Nevada, which have been intensively modified, especially reducing meadow wetness, which favors easy access for mammalian predators to reach nesting areas in the meadow interior. High nest predation frequency is one of the main factors for willow flycatcher and other passerines? populations decline. I conducted trapping in wet and dry areas on 10 meadows in May?August of 2007 and 2008 to identify the assemblage of potential mammalian nest predators. I compared the predator activity between wet and dry areas of the meadows and determined the relationship between predator activity with vegetation and hydrology of the meadows. In 2008, I used radio-telemetry on deer mice (Peromyscus maniculatus) and yellow-pine chipmunks (Tamias amoenus) to determine their movement patterns across wet and dry areas, and between forest and meadow. My results showed that chipmunks? and squirrels? activity was restricted almost to dry areas. The activity of yellow-pine chipmunks was 96% and 97% higher in dry versus wet areas in 2007 and 2008, respectively. Voles, mice, and shrews were active in both site types. Voles (Microtus spp.) and shrews (Sorex spp.) were in general more active in wet areas versus dry areas in 2007. Deer mice were equally active in both site types in 2007 and more active in wet areas in 2008. Between years, predators were 68% more active in wet areas in 2007 compared to 2008, and similarly 52% more active in dry areas. Radio-tagged deer mice used the forest and the meadow and were more common in dry areas, whereas yellowpine chipmunks used more the forest than the meadows and were active only in dry areas. Passerines nesting in drier areas are exposed to a larger assemblage of potential predators and are more likely to be predated. My results suggest that increasing the proportion of inundated areas in the meadows would help reduce predator activity (especially chipmunks and squirrels) and consequently nest predation, helping increase flycatcher numbers. In addition, wetter conditions will favor an increment in food availability for flycatchers and an increment in willow cover, which consequently will provide more nesting substrate and will help increase nest concealment.

Predation is the leading cause of nest failure in songbirds. My study identified nest predators of black-capped vireos and white-eyed vireos, quantified the activity of potential predator species, examined the relationships between vegetation and nest predators, and examined the relationship between nest predation and parasitism by brown-headed cowbirds. In 2008 and 2009 I monitored black-capped and white-eyed vireo nests on privately-owned properties in Coryell County and black-capped vireo nests on Kerr WMA in Kerr County and at Devils River State Natural Area in Val Verde County (2009 only). I monitored vireo nests using a video camera system to identify predators and nest fate. I also collected at-nest vegetation measurements including nest height, distance to nearest habitat edge, and nest concealment. Additionally, I sampled potential predator activity at a subset of black-capped vireo and white-eyed vireo nests in Coryell County using camera-trap bait stations and herptofaunal traps. I monitored 117 black-capped vireo nests and 54 white-eyed vireo nests. Forty-two percent of black-capped vireo and 35% of white-eyed vireo nests failed due to predation. I recorded >10 total predator species and 37 black-capped vireo and 15 white-eyed vireo nest predation events. Snakes (35%) and cowbirds (29%) were the most frequently identified nest predators; however, major predator species varied by location. I observed no significant relationship between nest fate (fledge vs. fail) and nest concealment or distance to edge for either vireo species. Nest height, concealment and distance to edge may relate to predator species in Coryell Co. for snake species, and Kerr for avian species. Additionally, I observed no difference between the predator activity and the fate of the nest. Both vireos have multiple nest predator species. Additionally, multiple cowbird predations demonstrate this species may have multi-level impacts on vireo productivity, even with active cowbird management. Vegetation structure and concealment may also affect predator species. However, the activity of other predator species near active nests may not negatively affect nest success.

Over the past century, populations of North American grassland songbirds have declined sharply as a consequence of habitat destruction. Alberta’s mixed-grass prairie constitutes Canada’s largest remaining tract of native grassland. However, this region has recently undergone a rapid expansion of conventional oil and natural gas development, and few studies have documented its effects on songbird nesting success. During the 2012-2014 breeding seasons, I monitored 813 nests of grassland songbirds located at sites that varied with respect to presence/absence, distance from, and types of oil and gas infrastructure (pump jacks, screw pumps, compressor stations) and gravel roads. Nest survival was significantly lower at infrastructure sites relative to controls for both Savannah sparrow and vesper sparrow. Additionally, vesper sparrow nest density was greater within 100 m of structures. These findings suggest that habitat disturbance caused by infrastructure may result in increased frequencies of nest predation at multiple spatial scales. / February 2016

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