Diurnal exposure as a risk sensitive behaviour in tawny owls Strix aluco?

Abstract

Tawny owls Strix aluco generally roost in cryptic locations during the day. To test the hypothesis that this cryptic behaviour is an effort to avoid mobbers or avian predators, we measured diurnal behaviour and cause-specific mortality of radiotagged birds. Non-breeding adults (assumed to be well fed individuals, optimising their own survival) roosted in less exposed locations than adults with young and newly independent juveniles. Parents roosted in the most exposed sites when their young were immature and vulnerable to depredation, probably to guard offspring. Newly independent juveniles apparently selected roosting sites in exposed places to get access to food, as this behaviour was associated with lower perching heights and higher prey abundance beneath their roosting sites. They also perched in more exposed sites, closer to the ground, in summers with low prey abundance compared to summers with high prey abundance. After previous encounters with goshawks Accipiter gentilis, dependent juveniles roosted in less exposed places compared to other young. The increased risk of being mobbed was highly significant with increasing roosting exposure. Once an owl was mobbed, the intensity of the mobbing correlated positively with the mass of the mobbers, but mobbing birds never killed any owls. In contrast, diurnal raptors caused 73% of natural owl deaths (n =15) and the depredation rate by raptors was 3.8 times higher in population classes that generally roosted in more exposed locations than did non-breeding adults. We therefore suggest that depredation by diurnal raptors is the main factor shaping the diurnal behaviour of tawny owls.P. Sunde (correspondence), M.

Kill before being killed: an experimental approach supports the predator-removal hypothesis as a determinant of intraguild predation in top predators

“…We suggest that the predator-removal hypothesis should also be tested in other interacting pairs of top predator species and in different conditions of density and resource availability. Another related step forward would be to understand if non-guild mobbers, alike IG mobbers, can also be preferential victims for dominant IG predators, as a way to reduce the costs of being mobbed (Pavey and Smyth 1998;Pettifor 1990;Sunde et al 2003). Finally, we recommend that future studies investigating the causes of IGP in vertebrates, should bear in mind the possibility of mutual IGP scenarios, and besides the competitive and energetic perspectives, the predator-removal behavioural mechanisms should also be included as potential triggers.…”

“…attacks were simply the result of an intruder's presence or a predation act), we performed an equal number of trials with a stuffed tawny owl Strix aluco dummy using the exact same procedure. The tawny owl is not an IG predator of the diurnal raptors involved in the experiment, but instead it can be seen as a competitor or a prey (Mikkola 1976;Sunde et al 2003). In Doñana National Park, tawny owls feed mainly on insects and small mammals, and frequently use raptors' nests to breed, overlapping in diet and habitat niches with the studied diurnal raptors (R. F. Lourenço, unpublished data).…”

Nest box use by American Kestrels and other cavity-nesting birds during the nonbreeding season

“…Roosting in closed sites such as cavities in winter provides more thermal benefits (Kendeigh 1961, Cooper 1999) and better protection from predators (Sunde et al 2003, Bock et al 2013 than roosting in open sites such as tree limbs. This is most likely why cavity-nesting species will use cavities as roosts in the nonbreeding season and preferentially choose them during winter months (Duguay et al 1997, Mainwaring 2011, Bock et al 2013.…”

Influence of anthropogenic features and traffic disturbance on burrowing owl diurnal roosting behavior

“…Individuals balan ce these factors to maximize their own fitness (Kerth et al 2001), but during the breeding season they may risk increased exposure to these elements to facilitate guarding mates and offspring (Sunde et al 2003). The success of a reproductive event may rely on the ability of a parent to efficiently detect and react to threats (Gotmark et al 1995, Magana et al 2010, highlighting the significance of daytime roost characteristics for nocturnal species.…”

“…The success of a reproductive event may rely on the ability of a parent to efficiently detect and react to threats (Gotmark et al 1995, Magana et al 2010, highlighting the significance of daytime roost characteristics for nocturnal species. The daytime activities of nocturnal animals is an understudied subject despite the higher predation risk that occurs during the day (Sunde et al 2003) and a greater potential for disturbance from human activities.…”