Stable isotope (C, N, O, and H) study of a comprehensive set of feathers from two Setophaga citrina

Oxygen, hydrogen, carbon and nitrogen stable isotopes were measured on a comprehensive sampling of feathers from two spring Hooded Warblers (Setophaga citrina) in Texas to evaluate isotopic variability between feathers and during molt. Isotopic homogeneity within each bird was found across all four isotopic systems, supporting the hypothesis that molt in these neotropical migrants is fully completed on the breeding grounds. This homogeneity suggests that the isotopic composition of a single feather is may be representative of the whole songbird. However, each bird was found to have one or two outlier feathers, which could signify regrowth of lost feathers after prebasic molt.

Stable isotope (C, N, O, and H) study of a comprehensive set of feathers from two Setophaga citrina

Oxygen, hydrogen, carbon and nitrogen stable isotopes were measured on a comprehensive sampling of feathers from two spring Hooded Warblers (Setophaga citrina) in Texas to evaluate isotopic variability between feathers and during molt. Isotopic homogeneity within each bird was found across all four isotopic systems, supporting the hypothesis that molt in these neotropical migrants is fully completed on the breeding grounds. Moreover, this homogeneity suggests that the isotopic composition of a single feather is typically representative of the whole songbird. However, each bird also has outlier feathers, which could signify regrowth of lost feathers after prebasic molt.

Influence of forest management on pre- and post-fledging productivity of a Neotropical migratory songbird in a highly fragmented landscape

Little is known about the effects of forest management on fledgling survival in birds, despite the fact that this is a key determinant of overall productivity. In 2005–2006, we compared male density, nesting success, and fledgling survival of Hooded Warblers (Wilsonia citrina Boddaert, 1783) among forest fragments that were reference sites (n = 3; not logged in >21 years) or had received either a standard selection system harvest (n = 3) or a heavy cut (n = 5) within the past 6–10 years. Density tended to be higher in logged sites than reference sites, but cumulative probability of nest survival (0.22 ± 0.02; 21 days) did not differ among treatments. Brown-headed Cowbird (Molothrus ater (Boddaert, 1783)) parasitism was significantly higher in recently logged sites, and reference sites produced significantly more Hooded Warbler young per successful nest than standard selection harvest sites. Logging treatment did not have a strong negative effect on fledgling survival, and overall, 51% (33/65) of fledglings survived until three weeks after fledging. Standard selection harvest sites had the highest Hooded Warbler density (0.2 males/ha) but also the lowest seasonal productivity (0.84 independent fledglings/female), raising the possibility of an ecological trap. The estimated number of daughters produced per female per year that are expected to survive to breeding age was lower for all treatments (reference, 0.26; selection, 0.17; heavy cut, 0.32) than the expected annual mortality probability of adult females (0.4–0.6). Forest fragments in this region appear to be population sinks, regardless of extent of partial harvest within the fragment.

Harvest-Related Edge Effects on Prey Availability and Foraging of Hooded Warblers in a Bottomland Hardwood Forest

The effects of harvest-created canopy gaps in bottomland hardwood forests on arthropod abundance and, hence, the foraging ecology of birds are poorly understood. I predicted that arthropod abundance would be high near edges of group-selection harvest gaps and lower in the surrounding forest, and that male Hooded Warblers (Wilsonia citrina) foraging near gaps would find more prey per unit time than those foraging in the surrounding forest. In fact, arthropod abundance was greater >100 m from a gap edge than at 0–30 m or 30–100 m from an edge, due to their abundance on switchcane (Arundinaria gigantea); arthropods did not differ in abundance among distances from gaps on oaks (Quercus spp.) or red maple (Acer rubrum). Similarly, Hooded Warbler foraging attack rates were not higher near gap edges: when foraging for fledglings, attack rate did not differ among distances from gaps, but when foraging for themselves, attack rates actually were lower 0–30 m from gap edges than 30–100 m or >100 m from a gap edge. Foraging attack rate was positively associated with arthropod abundance. Hooded Warblers apparently encountered fewer prey and presumably foraged less efficiently where arthropods were least abundant, i.e., near gaps. That attack rates among birds foraging for fledglings were not affected by distance from gap (and hence arthropod abundance) suggests that prey availability may not be limiting at any location across the forest, despite the depressing effects of gaps on arthropod abundance.Efectos de Borde Relacionados con la Cosecha Forestal sobre la Disponibilidad de Presas y el Forrajeo de Wilsonia citrina en un Bosque Leñoso RibereñoResumen. El efecto de la creación de claros en el dosel por la cosecha de árboles en bosques leñosos ribereños sobre la abundancia de artrópodos y por lo tanto sobre la ecología de forrajeo de las aves es poco entendido. En este estudio, predije que la abundancia de artrópodos sería mayor cerca de los bordes de claros producidos por tala selectiva en grupo y menor en el bosque circundante, y que los machos de Wilsonia citrina que forrajean cerca de los claros encontrarían más presas por unidad de tiempo que aquellos que forrajean en el bosque circundante. De hecho, la abundancia de artrópodos fue mayor a más de 100 m del borde de los claros que entre 0 y 30 m o entre 30 y 100 m desde un borde, debido a la abundancia de los artrópodos sobre Arundinaria gigantea. La abundancia de artrópodos sobre Quercus spp o Acer rubrum no fue diferente entre distintas categorías de distancia desde los claros. De manera similar, las tasas de ataque de forrajeo de W. citrina no fueron mayores cerca de los bordes de los claros: cuando se encontraban forrajeando para los polluelos, las tasas de ataque no fueron diferentes entre las distancias desde los claros, pero cuando se encontraban forrajeando para ellos mismos, las tasas de ataque fueron menores entre 0 y 30 m desde el borde de un claro a más de 30 m de un borde de un claro. La tasa de ataques de forrajeo se relacionó positivamente con la abundancia de artrópodos. Aparentemente, W. citrina encontró menos presas y posiblemente forrajeó de una manera menos eficiente donde los artrópodos eran menos abundantes, i.e., cerca de los claros. El hecho de que la tasa de ataque por parte de individuos que estaban forrajeando para sus polluelos no fuera afectada por la distancia a los bordes (y por lo tanto por la abundancia de artrópodos) sugiere que la disponibilidad de presas no parece ser limitante en ningún lugar del bosque, a pesar del efecto negativo de los claros sobre la abundancia de artrópodos.