Contrasting effects of climate on grey heron, malleefowl and barn owl populations Maria Boyle A and Jim Hone A,B A Institute for Applied Ecology, University of Canberra, Canberra, ACT 2601, Australia. B Corresponding author. Email: Jim.Hone@canberra.edu.au Abstract Context. The population dynamics of many wildlife species are associated with fluctuations in climate. Food and abundance may also influence wildlife dynamics. Aims. The present paper aims to evaluate the relative effects of climate on the annual instantaneous population growth rate (r) of the following three bird species: grey heron and barn owl in parts of Britain and malleefowl in a part of Australia. Methods. A priori hypotheses of mechanistic effects of climate are derived and evaluated using information theoretic and regression analyses and published data for the three bird species. Climate was measured as the winter North Atlantic Oscillation (NAO) for herons and owls, and rainfall and also the Southern Oscillation Index (SOI) for malleefowl. Key results. Population dynamics of grey heron were positively related to the winter NAO, and of malleefowl were positively related to annual rainfall and related in a non-linear manner to SOI. By contrast, population dynamics of barn owl were very weakly related to climate. The best models for the grey heron differed between time periods but always included an effect of the NAO. Conclusions. The annual population growth rate of grey heron, malleefowl and barn owl show contrasting relationships with climate, from stronger (heron and malleefowl) to weaker (barn owl). The results were broadly consistent with reported patterns but differed in some details. Interpretation of the effects of climate on the basis of analyses rather than visual assessment is encouraged. Implications. Effects of climate differ among species, so effects of future climate change may also differ. Additional keywords: barn owl, grey heron, malleefowl, numerical response, wildlife population dynamics. Received 17 December 2010, accepted 6 October 2011, published online 21 December 2011 Introduction Climate may directly and indirectly influence wildlife population dynamics (Andrewartha and Birch 1954; Caughley et al. 1987; Newton 1998). Climate may influence food availability and hence survival and fecundity rates of wildlife. Survival may be influenced because of effects on thermoregulation. Alternatively, climate may influence the ability of a population to convert food into population growth, separate from an effect on food availability. This latter possibility, the ability to convert food into population growth, is the focus of the present study. A considerable amount of annual variation in the size of bird populations (Sæther et al. 2003) and annual growth rate of mammal populations (Hone and Clutton-Brock 2007) has been reported as related to large-scale climate phenomena in the northern hemisphere, such as the winter North Atlantic Oscillation (NAO) (Hurrell et al. 2003; Stenseth et al. 2003). In the southern hemisphere, the Southern Oscillation Index (SOI) is an analogous large- scale climate index (Stenseth et al. 2003) and may also be related to wildlife dynamics. There are many examples in the literature of bird population dynamics being related to climate (Newton 1998; Knape and de Valpine 2011). Such associations have been described on the basis of visual assessment of apparent patterns or formal analysis, with the latter being encouraged. Three bird species were examined in the present study to re-evaluate, using analysis, some reported associations of dynamics and climate. The British Trust for Ornithology’s Census of Heronries for the grey heron (Ardea cinerea) has occurred annually in England and Wales since 1928. The data on heron abundance used herein have been described several times in the ecological literature (e.g. Stafford 1971; Putman and Wratten 1984; Caughley and Sinclair 1994; Begon et al. 2006), with the grey heron population reported to experience significant weather related population crashes because of severe winters and temperatures below freezing. The reports typically contain no formal analysis. These crashes are followed by relatively fast recovery periods (Stafford 1971; North and Morgan 1979). The fast recovery of the population indicates a return towards a dynamic equilibrium, suggesting that in addition to weather- CSIRO PUBLISHING Wildlife Research, 2012, 39,7–14 http://dx.doi.org/10.1071/WR10233 Journal compilation Ó CSIRO 2012 www.publish.csiro.au/journals/wr