Seasonal variation in foraging ecology of three species of overwintering Leaf Warblers (genus Phylloscopus) in the Himalayan foothills

Abstract

We studied a guild of overwintering Phylloscopus warblers (Hume's Warbler, Grey-hooded Warbler, Lemon-rumped Warbler) in the Himalayan foothills to gain an understanding of the manner in which they respond to changes in their habitat structure and resource availability from early to late winter (2006)(2007). The relative abundances of birds and vegetation attributes were quantified at 91 point count stations. Arthropod abundance was measured in both the tree and shrub layers. Foraging behaviour was characterized in terms of the following dimensions: foraging height, foraging tree species, foraging manoeuvre and foraging substrate. From early to late winter, we observed a significant decline in vegetation cover in the canopy layer and arthropod abundance in both the tree and shrub layers, but did not detect any associated decline in the relative abundance of the three species. While a general shift to lower foraging heights was observed in late winter, no significant seasonal variation could be detected at the species level in the other dimensions. Furthermore, though interspecific segregation by foraging heights remained conserved across winter, foraging segregation in terms of the use of foraging trees and manoeuvres emerged only in late winter. Our results suggest that a shift in foraging patterns enabled the guild to adjust to changes in habitat structure and decline in food availability in winter.Keywords Arthropod abundance Á Foraging behaviour Á P. humei Á P. xanthoschistos Á P. chloronotus Zusammenfassung Wir haben eine Gilde überwintern-der Phylloscopus-Laubsänger (Tienshan-Laubsänger, Grauscheitel-Laubsänger, Goldhähnchen-Laubsänger) in den Ausläufern des Himalajas untersucht, um zu verstehen, auf welche Art und Weise diese Laubsänger auf Verän-derungen der Habitatstruktur und Ressourcenverfügbarkeit vom Früh-bis zum Spätwinter (2006)(2007) reagieren. Die relativen Abundanzen der Vögel sowie Vegetationsmerkmale wurden von 91 Punktzählstationen aus quantifiziert. Die Abundanz von Arthropoden wurde sowohl in der Baum-als auch in der Strauchschicht gemessen. Das Nahrungssuchverhalten wurde im Hinblick auf folgende Parameter beschrieben: Höhe, Baumart, Manöver und Substrat für die Nahrungssuche. Vom Früh-bis zum Spätwinter haben wir eine signifikante Abnahme der Vegetationsbedeckung in der Kronenschicht und der Arthropodenabundanz in sowohl der Baum-als auch der Strauchschicht beobachtet. Es wurde allerdings keine damit verbundene Abnahme der relativen Abundanzen der drei Vogelarten festgestellt. Während sich die Nahrungssuche im Spätwinter allgemein in geringere Höhen verlagerte, konnten für die anderen Maße keine signifikanten jahreszeitlichen Schwankungen auf dem Artniveau festgestellt werden. Obwohl die verschiedenen Arten den ganzen Winter über in unterschiedlicher Höhe nach Nahrung suchten, zeichnete sich eine Trennung anhand der Baumarten und Manöver, die zur Nahrungssuche genutzt wurden, erst im Spätwinter ab. Daher deuten unsere Ergebnisse darauf hin, dass eine Verschiebung in den Communicated by F....

Temperature and competition interact to structure Himalayan bird communities

“…We expect that seasonal resource fluctuations should alter competition, and therefore coexistence or segregation in thermal niche space. Specifically, we expect greater congeneric segregation in thermal space in winter (when resources are scarce) than in summer (when resources are abundant; table 1: AB) [28]. Because the degree of seasonality is heightened in the west, we expect these patterns to be stronger for species in the western Himalayas (table 1: AB).…”

Conserving Himalayan birds in highly seasonal forested and agricultural landscapes

“…Although it is unclear why Himalayan birds extensively use agricultural lands during winter, it could be due to large reductions in arthropod abundance in forests in winter (Ghosh et al. ) or to seasonal diet switching (Grimmett et al. ) that enables species to capitalize on more diverse prey bases in agriculture.…”

“…In the Himalayas, dramatic seasonality brings widely fluctuating annual temperatures, resulting in seasonal surges in food resources (Ghosh et al. ). Consequently, the Himalayan fauna is continually in flux, with many species utilizing different habitats and resources in different seasons (Laiolo ).…”

Morphological and Behavioral Correlates of Long-Term Bird Survival in Selectively Logged Forest

“…Although elevational migration might serve to maximize yearround constancy in the climatic niche (Srinivasan et al, 2018), migration can also carry energetic and predation costs that offset benefits from enhanced resource availability in milder wintering grounds (Alerstam et al, 2003;Cooper et al, 2015;Rushing et al, 2017). At the same time, residents, despite being subject to food shortages in winter (Ghosh et al, 2011), might benefit from enhanced knowledge of resource and predators distribution on their territories (Sandercock and Jaramillo, 2002). Combined, these trade-offs might result in the lack of survival differences between residents and migrants in both intact and logged forest ( Figure 2D).…”