Effects of Climate on Chick Growth in the Black-legged Kittiwake (Rissa tridactyla)
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- Institutt for biologi 
Seabirds are declining worldwide as a result of anthropogenic influences, primarily through climate change affecting the food availability. One of the declining species is the black-legged kittiwake (Rissa tridactyla), whose breeding populations in Norway have declined by 60-80 % since the 1980 s. Chick growth is a good indicator of the environmental conditions as it reflects food availability during the rearing period, and affects post-fledging survival and population recruitment. The present study investigated the impact of various climatic variables on the growth rate of kittiwake chicks. This was done by using data on individual chick growth rates obtained during the breeding seasons of 2007 through 2015 from the island Anda, in northern Norway. The growth of 179 kittiwake chicks was assessed against the North Atlantic Oscillation winter index (NAOw), sea-surface temperatures of the pre-breeding and breeding season, precipitation, wind, and air temperature using a non-linear mixed effects model. Precipitation and NAOw were both shown to negatively affect the growth rate of the chicks. Precipitation presumably affects chick growth rates directly through increasing their energy budgets. The NAOw is assumed to affect chick growth through food availability, although no significant results were found between diets and the NAOw index. As chick growth is likely to affect post-fledging survival, increased knowledge on which climatic parameters affect the growth, and to what extent, is useful for distinguishing the effects of climate from other factors influencing the populations. This is important in order to direct management efforts towards all factors influencing the population development.