Post-fledging ecology and survival of neotropical migratory songbirds on a managed Appalachian forest

Abstract

POST-FLEDGING ECOLOGY AND SURVIVAL OF NEOTROPICAL MIGRATORY SONGBIRDS ON A MANAGED APPALACHIAN FOREST TIM DELLINGER During the post-fledging period, some juvenile songbirds appear to require early successional habitats at some level, suggesting that disturbance (whether natural or anthropogenic) in the landscape is important. Previous studies of juvenile Wood Thrushes (Hylocichla mustelina) have found them in early successional areas in which adults do not nest. My objective was to determine how juvenile Wood Thrushes used areas harvested through various silvicultural techniques within a forested landscape. I examined settled areas, habitat use, survival, and daily movements of 55 radio-tagged juvenile Wood Thrushes on a managed forest in the central Appalachian mountains of West Virginia during 2004 to 2005. I tagged individuals as nestlings and as juveniles, and radio-tracked birds in the natal and post-natal period. I used Global Positioning Systems to record the location of each bird on a daily basis and sampled habitat variables at these locations. All locations were assigned to one of three landcovers (mature forest, sawtimber harvests, and early successional areas) on a digitized map of the study site. I examined the proportion of daily locations within each landcover. I measured the size of harvests and related size and age to use by juvenile Wood Thrushes. Once independent from adults, most individuals preferred early successional areas, in particular large, older clearcuts, >13-ha in size and 7-11 years post harvest. Overall, radiotagged Wood Thrushes tended to move from open areas to those with a denser understory as they transitioned from being dependent on adults to being independent. Survival was similar among cover types (natal: P = 0.7, mature forest 91%, sawtimber harvest 80%, early successional area 88%; post-natal: 100% among all cover types). Radio-tagged juvenile Wood Thrushes on my study remained in the natal areas approximately 3 weeks before moving to post-natal sites. Similar to other studies, some individuals were located in up to 4 separate post-natal sites prior to migration or transmitter battery failure. Sizes of and duration within settled areas were similar to those documented in previous studies but distances between settled sites were shorter (natal to initial post-natal: x = vii TABLE OF CONTENTS

Effects of early‐successional shrubland management on breeding wood thrush populations

“…Nonetheless, the evidence for a link between use of shrublands and fledgling survival is equivocal. For wood thrushes, Dellinger () reported that survival rates of fledglings did not differ between mature forest, regenerating clearcuts, and thinned stands. On the other hand, King et al () reported that understory structure was positively associated with the survival of fledgling ovenbirds ( Seiurus aurocapilla ).…”

“…To locate study sites, we placed a 70 × 70‐m grid over the entire study region and measured the area of our 4 land‐use categories in a 2‐km radius around each grid cell. We used 2 km as a radius because the mean dispersal distance reported for wood thrush fledglings leaving their natal territories is <2 km (Anders et al , Vega‐Rivera et al , Dellinger ). Development and agriculture can reduce avian nest success (Rodewald et al , Phillips et al ), so we eliminated sites where the combined cover of agriculture and development in the 2‐km buffer zone was ≥2% of the land area.…”

“…A chief obstacle in resolving this issue is the lack of studies in which access by fledglings to early‐successional shrublands is restricted. Most studies of fledgling mature‐forest birds have occurred in landscapes where birds are free to choose among early‐ or later‐successional stands (Vega‐Rivera et al , Dellinger , Vitz , Streby and Andersen ). Fledglings are mobile and can disperse several kilometers from nest sites to post‐fledging areas (Anders et al , Vitz and Rodewald ).…”