Shared space, individually used: spatial behaviour of non-breeding ravens (Corvus corax) close to a permanent anthropogenic food source

Abstract

Natal dispersal is a well-studied phenomenon that can be divided into three stages: (1) starting from an area, (2) wandering to another area and (3) either settling in that area to breed or merely temporarily stopping there before continuing to wander. During the third phase, we can distinguish breeders from non-breeders, which may show similar or different patterns of space use. Breeding Common Ravens are territorial year-round; non-breeders are highly vagrant but may gather at food sources and night roosts for varying lengths of time. In contrast to the wandering phase, little is known about the space use of ravens at such ''stop'' sites. Here, we used radio telemetry to investigate the space use of 21 non-breeding ravens in the Austrian Alps during a stop stage at an anthropogenic food source. The tagged ravens were present in 69.2 % of the relocation attempts. They used only 27.0 ha (range 6.7-59.7 ha, 95 % utilisation distribution) of the study area, and their activity ranges strongly overlapped with each other. However, within this shared space, sub/adult non-breeders could be found at individually distinct locations, while juveniles showed similar spatial distributions. These results, combined with reported long-distance movements, underline the high behavioural flexibility of non-breeding ravens, which may be a reason for their success in very different habitats throughout the Northern Hemisphere.

Common raven movement and space use: influence of anthropogenic subsidies within greater sage‐grouse nesting habitat

“…, Loretto et al. ). It is likely that breeding ravens would take advantage of point‐source subsidies (Kristan et al.…”

“…We only considered GPS locations for ravens of any breeding status within this window within each year to avoid comparing seasonally varying movement behaviors of nonbreeding birds with movement behaviors of breeding birds (Loretto et al. ). Second, we considered four temporally mutually exclusive breeding statuses to which we assigned each raven GPS location: breeding, post‐failed nest, post‐successful nest, and nonbreeding.…”

“…Nonbreeding ravens frequently visited pointsource subsidies and did so significantly more often than post-failed ravens (12.5% vs. 1.2% of each individual's locations) or post-successful and breeding ravens, which rarely visited pointsource subsidies (0.1% and 0.0%, respectively). This is likely explained by previous findings that breeding ravens forage intensively in the area surrounding their nest (Kristan et al 2004, R€ osner andSelva 2005), whereas nonbreeding ravens can adapt flexible space use patterns to take advantage of anthropogenic food sources over large areas (Heinrich et al 1994, Webb et al 2012, Loretto et al 2015. It is likely that breeding ravens would take advantage of pointsource subsidies (Kristan et al 2004, Roth et al 2004, Kristan and Boarman 2007, but only when their nests were already close to those subsidies (Kristan et al 2004).…”

“…First, we designated the breeding season for all ravens within each year as six days before the earliest date that any raven began incubation until 14 d after successful fledging of the latest breeding raven (Stiehl 1985). We only considered GPS locations for ravens of any breeding status within this window within each year to avoid comparing seasonally varying movement behaviors of nonbreeding birds with movement behaviors of breeding birds (Loretto et al 2015). Second, we considered four temporally mutually exclusive breeding statuses to which we assigned each raven GPS location: breeding, post-failed nest, post-successful nest, and nonbreeding.…”

Ravens adjust their antipredatory responses to con‐ and hetero‐specific alarms to the perceived threat

“…The ravens forage in the game park most often between 8 and 10 a.m., when the captive wild boars, bears and wolves are provided with food (Loretto, Reimann, Schuster, Graulich, & Bugnyar, ). Therefore, we ran the experiments right after the feeding to be sure that sufficient numbers of birds were present.…”