The impact of climate and cyclic food abundance on the timing of breeding and brood size in four boreal owl species

Abstract

The ongoing climate change has improved our understanding of how climate affects the reproduction of animals. However, the interaction between food availability and climate on breeding has rarely been examined. While it has been shown that breeding of boreal birds of prey is first and foremost determined by prey abundance, little information exists on how climatic conditions influence this relationship. We studied the joint effects of main prey abundance and ambient weather on timing of breeding and reproductive success of two smaller (pygmy owl Glaucidium passerinum and Tengmalm's owl Aegolius funereus) and two larger (tawny owl Strix aluco and Ural owl Strix uralensis) avian predator species using long-term nation-wide datasets during 1973-2004. We found no temporal trend either in vole abundance or in hatching date and brood size of any studied owl species. In the larger species, increasing late winter or early spring temperature advanced breeding at least as much as did high autumn abundance of prey (voles). Furthermore, increasing snow depth delayed breeding of the largest species (Ural owl), presumably by reducing the availability of voles. Brood size was strongly determined by spring vole abundance in all four owl species. These results show that climate directly affects the breeding performance of vole-eating boreal avian predators much more than previously thought. According to earlier studies, small-sized species should advance their breeding more than larger species in response to increasing temperature. However, we found an opposite pattern, with larger species being more sensitive to temperature. We argue that this pattern is caused by a difference in the breeding tactics of larger mostly capital breeding and smaller mostly income breeding owl species.

Capital and income breeding: the role of food supply

“…Storage strategies of plants (Chapin et al 1990) have implications for areas as topical as carbon sequestration and crop yield. Among animals, patterns of energy storage have provided insight into the strategies used by organisms to cope with seasonal environments and other stressors, including climate change (Anthony et al 2009, Lehikoinen et al 2011. A specific aspect of energy storage that has seen increasing interest over recent decades is that of the distinction between capital and income breeders (Jo¨nsson 1997, Bonnet et al 1998, Meijer and Drent 1999, Klaassen et al 2001, Houston et al 2007, Stephens et al 2009).…”

Factors Affecting Timing of Breeding in the Tawny Owl

“…8,10,20]. In the North, the availability of food for breeding tawny owls seems to be particularly affected by the pronounced and more or less cyclic fluctuations of vole populations [21][22][23][24] and it is modified by habitat [25,26] and various climatic factors [8,20,22,27,28].…”

Range Extensions of Some Boreal Owl Species: Comments on Snow Cover, Ice Crusts, and Climate Change

“…clImate chanGe and Boreal owls Both higher temperature and higher food abundance can separately lead to advancement of owl breeding (Hipkiss et al, 2008), and both timing of breeding and breeding success might be affected (Lehikoinen et al, 2011). Milder climate can improve body condition and winter survival of boreal owls because increasing temperature lowers their energy requirements and decreased snow depth may improve hunting success (Hipkiss et al, 2008).…”

“…Conditions of breeding birds might be enhanced if the winter has been mild, allowing individuals to breed earlier. Studies of the performance of boreal forest owls confirm that it is to a substantial degree determined by weather conditions and not just by the abundance of their main prey (Lehikoinen et al, 2011). Interaction between food availability and climate on breeding has been studied, and increased snow depth might indicate delayed breeding of at least one large species, the Ural owl (Lehikoinen et al, 2011).…”