Aggressive behaviour and nest-site defence during the breeding season in an island kestrel population
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ARTICLE
Aggressive behaviour and nest-site defence during the breeding season in an island kestrel population Jose´ Carrillo • Enrique Gonza´lez-Da´vila
Received: 3 December 2012 / Accepted: 22 February 2013 / Published online: 19 March 2013 Ó Japan Ethological Society and Springer Japan 2013
Abstract We examined the changes in the intensity of intra-specific aggression (ISA) in a kestrel (Falco tinnunculus canariensis) population throughout the breeding season, in order to evaluate the main hypotheses regarding ISA (defence of parentage, food, nest-site and offspring). Each pair was presented with a live caged adult male or female as a conspecific intruder. The intensity of ISA did not vary significantly during the breeding season, and nor did it correlate with offspring value, or food availability. Our island-dwelling kestrel population showed low fluctuation in ISA during the breeding season, and similar levels of aggression in both members of the pair towards male or female intruders. These findings support the nestsite defence hypothesis. Pairs with more exposed nestsites showed increased ISA, unexplained by offspring value. We suggest that this behaviour is related with nest-site conspicuousness and vulnerability. The pairs displaying greater ISA also showed greater aggression towards humans, the main local predator. This may indicate that defensive behaviour evolved in the past when it was advantageous against predators, and became a trait. Compared with the non-island reference population, we only found differences in ISA during the pre-laying phase: lower intensity of aggressive behaviour between males, and higher between females.
J. Carrillo (&) Department of Parasitology, Ecology and Genetics, Faculty of Biology, University of La Laguna, Avenue Astrofı´sico Francisco Sa´nchez s/n, 38206 La Laguna, Tenerife, Spain e-mail: [email protected] E. Gonza´lez-Da´vila Department of Statistics, O. R. and Computation, Faculty of Mathematics, University of La Laguna, Avenue Astrofı´sico Francisco Sa´nchez s/n, 38206 La Laguna, Tenerife, Spain
Keywords Breeding season Eurasian kestrel Falco tinnunculus Intra-specific aggression Islands Nest-site defence
Introduction Intra-specific aggression (ISA) in birds during the breeding season involves time and energy expenditure to protect mates, offspring and territorial resources such as nest-sites and food. Several theoretical and empirical studies have postulated that patterns of ISA during the breeding season reflect the need to defend resources (Brown 1964; MacLean and Seastedt 1979; Gowaty 1981; Birkhead and Møller 1992; Wiklund and Village 1992; Garcı´a and Arroyo 2002; Neudorf 2004): 1.
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If the defence of breeding territory implies the protection of parentage or avoidance of kleptogamy, aggression by both members of the pair should be most intense during the fertile period and laying; the male should be more aggressive than the female and aggression should be intra-sexual. If the defence involves food, the aggression of both members of the pair shou
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