Seasonal diets of insectivorous birds using canopy gaps in a bottomland forest

Abstract

Little is known about how insectivorous bird diets are influenced by arthropod availability and about how these relationships vary seasonally. We captured birds in forest-canopy gaps and adjacent mature forest during 2001 and 2002 at the Savannah River Site in Barnwell County, South Carolina, and flushed their crops to gather information about arthropods eaten during four periods: spring migration, breeding, postbreeding, and fall migration. Arthropod availability for foliage-and ground-gleaning birds was examined by leaf clipping and pitfall trapping. Coleopterans and Hemipterans were used by foliage-and ground-gleaners more than expected during all periods, whereas arthropods in the orders Araneae and Hymenoptera were used as, or less than, expected based on availability during all periods. Ground-gleaning birds used Homopterans and Lepidopterans in proportions higher than availability during all periods. Arthropod use by birds was consistent from spring through fall migration, with no apparent seasonal shift in diet. Based on concurrent studies, heavily used orders of arthropods were equally abundant or slightly less abundant in canopy gaps than in the surrounding mature forest, but bird species were most frequently detected in gaps. Such results suggest that preferential feeding on arthropods by foliage-gleaning birds in gap habitats reduced arthropod densities or, alternatively, that bird use of gap and forest habitat was not determined by food resources. The abundance of arthropods across the stand may have allowed birds to remain in the densely vegetated gaps where thick cover provides protection from predators. SINOPSIS. Dieta estacional de aves insectivoras usando huecos del docel en bosques de maderas durasSe conoce poco de como la dieta de insectívoros está influenciada por la disponibilidad de artrópodos y de como estas interacciones varían estacionalmente. Capturamos aves en huecos o aberturas del docel de un bosque, adyacente a un bosque maduro durante el 2001 y el 2002 en Savannah River Site, Condado Garnwell, Carolina del Sur. A las aves le lavamos el buche para obtener información sobre los artrópodos utilizados como alimento durante la migración primaveral, durante laépoca reproductiva, post-reproductiva y durante la migración otoñal. Para determinar la disponibilidad de artrópodos en el follaje y en el suelo, usamos la técnica de cortar hojas con artrópodos y la de trampas de envases en el suelo. Los coleópteros y los hemípteros fueron utilizados como fuente de alimento, más de lo esperado tanto por aves que se alimentaron en el follaje como en los suelos, durante todos los periodos. Por su parte, los arácnidos y los himenópteros, fueron utilizados menos de lo esperado, basándose en la disponibilidad de estos durante todos los periodos de estudio. Las aves que se alimentaron en los suelos utilizaron homópteros y lepidópteros en mayor proporción que lo esperado, dada su disponibilidad, durante todos los periodos. Los artrópodos utilizados por las aves fueron consistentes desde la primavera hasta...

Forest management and temporal effects on food abundance for a ground-foraging bird (Catharus guttatus)

“…Our study suggests that this may be due to higher food abundance as percent shade decreases in gaps. Our findings support one alternative hypothesis put forth by Moorman et al (2007): that increased bird use of canopy gaps is due to increased food abundance. However, Greenberg and Forrest (2003) found that abundance of most arthropod taxa measured (including Carabidae and Araneae) was lower in canopy gaps compared to control forest plots.…”

Diet of three insectivorous birds in Nagapattinam District, Tamil Nadu, India – a preliminary study

“…These three species were predominantly found in agricultural lands and the above insect prey formed principal food items due to their greater availability. Moorman et al (2007) reported that Coleopterans and Hemipterans formed the major diet of foliage-gleaning and ground-gleaning insectivorous birds. Many other investigators also have determined Coleopterans, Hemipterans and Hymenopterans (Mason & Maxwell-Lefroy 1912;Sodhi 1986;Kaspari & Joern 1993;Parasharya et al 1994;Sivakumaran & Thiyagesan 2003;Yard et al 2004;Asokan et al 2008) as primary food resource of insectivorous birds.…”

Why are woodland-dependent avian insectivore populations vulnerable to declines in highly-modified landscapes?

“…Prey vary in nutritional value (Robel et al 1995;Arnold et al 2010;Razeng & Watson 2015) and this may influence birds to preferentially target certain taxa (Razeng & Watson 2015). Additionally, birds employ specific strategies, such as foraging in a certain strata, using particular capture methods, or feeding at a certain time of day (Higgins & Peter 2002;Antos & Bennett 2006;Moorman et al 2007) and invertebrate sampling methods need to take these into consideration. Thus, it is unclear whether it is appropriate to treat all prey equally in food availability studies and greater understanding of the issue may be derived by taking some of these factors into consideration.…”

“…Instead of basing this investigation on total invertebrate density as is often done (Burke & Nol 1998;Zanette et al 2000), I only consider prey taxa known to be consumed by robins. Drawing inferences based on total invertebrate density may be misleading given that birds show preferences towards certain prey groups (Naef-Daenzer et al 2000;Hagar et al 2007;Moorman et al 2007;Razeng & Watson 2012 Maron et al (2012) and what these changes might mean for the population.…”

“…Birds show preferences for particular prey taxa (Naef-Daenzer et al 2000;Hagar et al 2007;Moorman et al 2007) which vary in nutritional value (Robel et al 1995;Razeng & Watson 2015). Additionally, birds may exhibit specific foraging behaviours that target certain prey taxa, such as foraging within particular strata (Antos & Bennett 2006;Moorman et al 2007). Furthermore, invertebrate taxonomic groups respond idiosyncratically to patch area (Didham 1997;Vasconcelos & Bruna 2012).…”