Long-term trends in survival of a declining population: the case of the little owl (<Emphasis Type="Italic">Athene noctua</Emphasis>) in the Netherlands |
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Authors: | Pascaline J Le Gouar Hans Schekkerman Henk P van der Jeugd Arjan Boele Ronald van Harxen Piet Fuchs Pascal Stroeken Arie J van Noordwijk |
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Institution: | (1) Vogeltrekstation––Dutch Centre for Avian Migration and Demography, NIOO-KNAW, P.O. Box 40, 6666 GA Heteren, The Netherlands;(2) SOVON Dutch Center for Field Ornithology, Rijksstraatweg 178, 6573 DG Beek-Ubbergen, The Netherlands;(3) STONE, De Kistemaker 12, 1852 GW Heiloo, The Netherlands;(4) Reeboklaan 6, 6705 BD Wageningen, The Netherlands;(5) Animal Ecology, NIOO-KNAW, P.O. Box 40, 6666 GA Heteren, The Netherlands;(6) Present address: UMR 6553 UR1-CNRS EcoBio, Station biologique, University of Rennes 1, 35380 Paimpont, France |
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Abstract: | The little owl (Athene noctua) has declined significantly in many parts of Europe, including the Netherlands. To understand the demographic mechanisms
underlying their decline, we analysed all available Dutch little owl ringing data. The data set spanned 35 years, and included
more than 24,000 ringed owls, allowing detailed estimation of survival rates through multi-state capture–recapture modelling
taking dispersal into account. We investigated geographical and temporal variation in age-specific survival rates and linked
annual survival estimates to population growth rate in corresponding years, as well as to environmental covariates. The best
model for estimating survival assumed time effects on both juvenile and adult survival rates, with average annual survival
estimated at 0.258 (SE = 0.047) and 0.753 (SE = 0.019), respectively. Juvenile survival rates decreased with time whereas
adult survival rates fluctuated regularly among years, low survival occurring about every 4 years. Years when the population
declined were associated with low juvenile survival. More than 60% of the variation in juvenile survival was explained by
the increase in road traffic intensity or in average temperature in spring, but these correlations rather reflect a gradual
decrease in juvenile survival coinciding with long-term global change than direct causal effects. Surprisingly, vole dynamics
did not explain the cyclic dynamics of adult survival rate. Instead, dry and cold years led to low adult survival rates. Low
juvenile survival rates, that limit recruitment of first-year breeders, and the regular occurrence of years with poor adult
survival, were the most important determinants of the population decline of the little owl. |
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