How Predictability of Feeding Patches Affects Home Range and Foraging Habitat Selection in Avian Social Scavengers?

Abstract

Feeding stations are commonly used to sustain conservation programs of scavengers but their impact on behaviour is still debated. They increase the temporal and spatial predictability of food resources while scavengers have supposedly evolved to search for unpredictable resources. In the Grands Causses (France), a reintroduced population of Griffon vultures Gyps fulvus can find carcasses at three types of sites: 1. “light feeding stations”, where farmers can drop carcasses at their farm (spatially predictable), 2. “heavy feeding stations”, where carcasses from nearby farms are concentrated (spatially and temporally predictable) and 3. open grasslands, where resources are randomly distributed (unpredictable). The impact of feeding stations on vulture’s foraging behaviour was investigated using 28 GPS-tracked vultures. The average home range size was maximal in spring (1272±752 km2) and minimal in winter (473±237 km2) and was highly variable among individuals. Analyses of home range characteristics and feeding habitat selection via compositional analysis showed that feeding stations were always preferred compared to the rest of the habitat where vultures can find unpredictable resources. Feeding stations were particularly used when resources were scarce (summer) or when flight conditions were poor (winter), limiting long-ranging movements. However, when flight conditions were optimal, home ranges also encompassed large areas of grassland where vultures could find unpredictable resources, suggesting that vultures did not lose their natural ability to forage on unpredictable resources, even when feeding stations were available. However during seasons when food abundance and flight conditions were not limited, vultures seemed to favour light over heavy feeding stations, probably because of the reduced intraspecific competition and a pattern closer to the natural dispersion of resources in the landscape. Light feeding stations are interesting tools for managing food resources, but don’t prevent vultures to feed at other places with possibly high risk of intoxication (poison).

Environmental drivers of variability in the movement ecology of turkey vultures (Cathartes aura) in North and South America

“…We believe that the extraordinary amount of daily movement during the non-migratory seasons is best explained by the species' extremely efficient soaring behaviour, which reduces the cost considerably [3]. We suggest that the relationship between range size and NDVI is due to the likelihood of reduced carcass availability in less productive breeding areas and, therefore, the need for larger searching areas, a relationship that also occurs in Old-World vultures [23,24]. Furthermore, as increased temperature correlates positively with thermal uplifts in both breeding areas ( p , 0.001, R 2 ¼ 0.08, d.f.…”

“…As datasets and collaborations grow, it will be necessary to find the time and expertise needed to manage, analyse and describe data using methods that move beyond simple maps and descriptive statistics. In our turkey vulture example, this will include path-annotation analysis [41] and comparative investigations of Old-World vultures (family Accipitridae) being tracked by us and other researchers [23,24,40]. Many resources currently exist to support these goals.…”

“…breeding and non-breeding). Specifically, environmental variables that make flight more energetically cost-effective will lead to larger home ranges, whereas variables that are indicative of increased food availability will result in a reduced need to move and thus a smaller home range [23,24]. Finally, because of seasonal differences in the internal drivers of movement, we expect that (Pr8) the effect of environmental variables on home-range size will be different on the breeding versus wintering grounds.…”

Using High-Resolution GPS Tracking Data of Bird Flight for Meteorological Observations

“…Since 2010, 22 griffon vultures from a colony in the Grands Causses area, southern France, were equipped with GPS tags from the UvA-BiTS system ) in order to study their foraging behavior [see additional details in Monsarrat et al (2013)]. The solar-powered GPS tags weigh about 45 g and contain a triaxial accelerometer, rechargeable battery, datalogger, and a two-way communication system, which makes it possible to remotely download data and change the measurement interval .…”

“…The area has a dry and su n ny Med iter r a ne a n climate. The home range of this resident griffon vulture population is located within a radius of roughly 50 km around the main colonies (g loba l home range area used by all birds approaches 10,000 km 2 ) (Monsarrat et al 2013). According to accelerometer data, griffon vultures almost exclusively use circling and gliding flight and flap only very rarely, typically at takeoff (Shepard Duriez et al 2014).…”