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| From 1976 to 1997 passerines were mist-netted and ringed on the island of Christiansø,
in the Baltic Sea. Here we present analyses of phenological changes (i.e. time of arrival)
for 25 species based on the entire populations of mist-netted songbirds during spring
migration. We used two approaches (least square and quantile regression) to test for
changes in arrival time of first individuals and three different parts of the songbird
populations (i.e. first 5%, 50% and 95% of the total number of trapped individuals
corrected for trapping effort). Our results generally confirm earlier spring arrival of
migratory passerines with an overall earlier arrival of 0.26 days per year. Changes in the
arrival time of first individuals are often the only data available. They are typically
analysed on the assumption that they are representative of their respective population.
We found a unidirectional, significant change towards earlier arrival for all four
measures of arrival timing which seem to support this. However, the four measures of
arrival are changing at different rates. First individuals changed arrival time more
rapidly than the first 5%, 50% and 95% of the spring total. Such differences are likely to
be important for our understanding of population-dynamic changes in relation to
climate change. These differences may also have long-term evolutionary consequences.
Migration distance seems to affect the degree of change in arrival time, but we found no
difference between species wintering in different regions of Africa. | |
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