An evaluation of reproductive success, adult survivorship and habitat use of shrubland birds on conservation-managed fields in western Connecticut

Loss of shrubland habitat has caused a steep decline in shrubland bird species across their ranges. Despite the trends, shrubland-specific management is poorly understood and has not been widely implemented in areas of shrubland bird decline. Annual adult survival, fecundity (the number of females produced by breeding females), philopatry (nestlings returning to their birth site) and nest survival (the probability of nests producing at least one fledgling) are important vital rates that are necessary to understanding population (source-sink) dynamics of a species. Nest site selection and predator identification are also important to understanding how vegetation and other variables affect nest survival, particularly in regard to predation. Threat of predation may also affect sleep patterns, particularly of females who sleep on the nest to thermoregulate nestlings. Little is known about sleep patterns of nesting migratory songbirds in the field which is important to understanding the evolutionary role predation plays on sleep behavior. To evaluate if conservation-managed fields are beneficial habitat to declining shrubland bird species my research objectives were to, (1) summarize and compare prior studies estimating nest survival of four declining shrubland bird species, Blue-winged Warbler ( Vermivora pinus), Prairie Warbler (Dendroica discolor), Indigo Bunting (Passerina cyanea) and Field Sparrow ( Spizella pusilla), to rates estimated from conservation-managed fields, (2) estimate apparent annual survival (phi), capture probability ( p) and philopatry rates of these four species on conservation-managed fields, (3) identify nestling predators through video, model the effects of nest site vegetation, nest area vegetation, proximity to edge, seasonal time, and annual time variables on daily nest survival of these four species, and conduct source-sink estimation to evaluate conservation-managed fields in comparison to previous studies in the literature, (4) evaluate three nest site selection hypotheses: Potential Prey (predation decreases in patches with more nest plant vegetation), Habitat Complexity (predation decreases in spatially complex habitats), and Nest Placement Co-existence (species that occupy similar nest site habitat structure have increased predation) to provide management guidance, and (5) use video cameras to document nighttime nest behavior of adult birds of these species. This study was conducted in Southbury, Connecticut from 2004 through 2008 on 23 ha of conservation-managed fields, which are actively maintained, dense shrublands dominated by native shrub species. A total of 125 nests of the four species were monitored every three days, mist nets were used to capture 228 adults, 173 nestlings were banded in the nest, and video cameras recorded nest predators and nighttime behavior at 11 nests. Vegetation and edge variables were measured at nests and in 20 m plots surrounding nests. These species generally had higher nest survival relative to prior studies in other shrubland management types/geographic areas. For most years annual apparent survival was higher than the average shrubland bird survival for Blue-winged Warbler and Prairie Warbler and was above or near average for Indigo Bunting and Field Sparrow. Adult survival was highest for Prairie Warbler (0.64+/-0.24 (SE) to 0.81+/-0.13) and Blue-winged Warbler (0.30+/-0.22 to 0.72+/-0.26). Indigo Bunting and Field Sparrow survival rates were (0.33+/-0.18 to 0.57+/-0.20) and (0.32+/-0.1 to 0.49+/-0.14), respectively. Juvenile philopatry was low, 2.3%, and recapture probabilities were constant among species and between years. Sex was important to adult survival of all species, except Blue-winged Warbler. Time, both constant and linear, was important to adult survival of all species Time was only important to nest survival of Blue-winged Warbler and Prairie Warbler. Daily nest survival estimates (+/-SE) were 0.959+/-0.019 for Blue-winged Warbler, 0.979+/-0.013 for Prairie Warbler, 0.986+/-0.013 for Indigo Bunting, and 0.972+/-0.011 for Field Sparrow. Amount of woody vegetation was the only variable affecting nest survival of all species, but response to increases in this variable was positive for both warbler species and negative for Indigo Bunting and Field Sparrow. Conservation-managed fields were the only source habitat for Blue-winged Warbler and Prairie Warbler when compared to other studies. Habitat Complexity best explained nest site selection of Blue-winged Warbler and Indigo Bunting. Potential Prey was the best explanation for nest site selection by Prairie Warbler. Females of all species awoke or maintained vigils often during the night with short periods of sleep, a behavior attributed to predation threat. Conservation-managed fields have higher nest survival rates, adult annual survival rates, and fecundity than reported in prior studies, and subsequently are source habitat for some shrubland bird species. Shrubland management should consider that vegetation effects on nest survival are species-specific.