Using multiple data sources to investigate foraging niche partitioning in sympatric obligate avian scavengers

Abstract

As carrion feeders competing for a limited and ephemeral resource, avian scavengers are ideal model organisms to study mechanisms of niche partitioning. Previous work has focused on observations of species' interactions at carcasses, and although fruitful, the inclusion of behavior beyond that at carcasses, such as movement patterns, could yield a more comprehensive understanding of mechanisms of foraging niche partitioning. Our goal was to assess how differences in physiological, morphological, and social characteristics between sympatric black vultures (Coragyps atratus) and turkey vultures (Cathartes aura) manifest interspecific variation in movement patterns, foraging habitats, and carcass use to reduce direct competition. Both species are obligate scavengers that co-occur across much of the New World. Turkey vultures are solitary foragers with enhanced olfactory capabilities and wings optimized for energy-efficient low-altitude soaring. Black vultures are aggressive, heavier bodied, and forage socially. We assessed interspecific variation in carcass exploitation using experimental carcass trials encompassing a range of habitats, carcass sizes, and seasons, and used GPS telemetry to compare how soaring conditions influenced daily space use and diurnal patterns of movement activity for each species. Turkey vultures occurred more often at small (i.e., rabbit) carcasses, and those obscured by forest cover than black vultures, and were the first vultures recorded at 94% of carcasses visited by both species. Both species increased movement rates and daily ranges when soaring conditions were favorable; however, turkey vultures had higher travel rates regardless of soaring conditions. Our results suggest the olfactory sense of turkey vultures allows them to locate smaller and visually obscured carcasses more efficiently than black vultures, facilitated by wing morphology that allows them to forage over large areas efficiently. Socially foraging black vultures appear specialized at locating larger carcasses in open habitats, which does not require as much foraging flight as turkey vultures. Our study illustrates how inclusion of movement ecology into niche partitioning studies provides a more complete understanding of the mechanisms of coexistence in avian scavenger guilds. This approach may provide important information to guide conservation efforts, such as supplemental feeding, of imperiled vulture species.

Functional traits driving species role in the structure of terrestrial vertebrate scavenger networks

“…These species are well known to be highly efficient scavengers (Sebasti an-Gonz alez et al 2016, Mateo-Tom as et al 2017, Morales-Reyes et al 2017. Vultures specialize in the consumption of carrion Houston 2004, Cort es-Avizanda et al 2014), and they can outcompete other vertebrates for carrion resources (Byrne et al 2019). Other species, such as mesopredators, can also monopolize carcasses in human dominated landscapes devoid of large mammalian predators (DeVault et al 2011, Buechley andS ßekercio glu 2016), whereas bear species Ursus spp.…”

Unravelling the vertebrate scavenger assemblage in the Gobi Desert, Mongolia

“…For example, Turner et al (2017) found that carrion detection times were 50% larger in habitats with more vegetation cover, especially during the warm season. In addition, vegetation cover can influence species composition, with species with developed sense of smell appearing in areas with more cover rather than species more dependent on visual cues (Byrne et al, 2019). Also, birds are expected to occur more often in open than in dense forest areas, where mammals tend to be more abundant (Pardo-Barquín et al, 2019).…”

How do Snow Partridge (Lerwa lerwa) and Tibetan Snowcock (Tetraogallus tibetanus) coexist in sympatry under high‐elevation conditions on the Qinghai–Tibetan Plateau?

“…A previous study suggested that body size differences among sympatric bird species facilitate community coexistence (Leyequién et al, 2007). Therefore, we consider that the differences in the use of ridge crests help form of niche divergence adopted by sympatric mammals and birds that allows the coexistence of related species (Byrne et al, 2019;Cui et al, 2008;Namgail et al, 2004;Wei et al, 1999). An et al (2009) suggested that the current geographic range of T. tibetanus has been influenced by the most recent large-scale glaciations on the QTP in and before the Pleistocene.…”

“…Habitat partitioning based on ridge crests serves to reduce both interference and competition, facilitating the coexistence of ecologically similar species. Habitat partitioning is a widespread form of niche divergence adopted by sympatric mammals and birds that allows the coexistence of related species (Byrne et al, 2019 ; Cui et al, 2008 ; Namgail et al, 2004 ; Wei et al, 1999 ). An et al ( 2009 ) suggested that the current geographic range of T .…”

“…The outstanding biodiversity of QTP in concert with its unique environment makes this hotspot ideal for researching species coexistence in mountainous regions. Previous studies investigating the QTP region have shown various examples of sympatric range via ecological separation in birds and mammals through mechanisms such as habitat partitioning, a partition of the environment in ways that minimizes interspecific competition (Bhatnagar et al, 2000 ; Byrne et al, 2019 ; Cui et al, 2008 ; Namgail et al, 2004 ; Wei et al, 1999 ). Although several studies have performed ecology‐related analyses of biodiversity at a broad scale across the QTP (e.g., Ding et al, 2006 ; Xu et al, 2017 ), to our knowledge, there remains insufficient research to explain the mechanisms facilitating species coexistence in high‐elevation areas (Fjeldså & Rahbek, 2006 ; Jetz & Rahbek, 2002 ; Rahbek et al, 2007 ).…”