Aankomst, doortrek en vertrek van de Huiszwaluw Delichon urbicum in Nederland in relatie tot een opwarmend klimaat

Arrival, migration and departure of House Martin Delichon urbicum in The Netherlands in relation to global warming The House Martin is a common migrant as well as a common breeding bird in The Netherlands. For this paper data on first arrival (phenology) and counts of visible bird migration are analysed. During 1978-’93 highly standardized counts of migrant birds were conducted in the Netherlands. During 1994-2012 these counts were less standardized and lasted one or more hours during the day lenght period. Data of one of the most standardized observation sites (1982-2002) were analysed seperatly. Data on first arrival were sampled around the city of Arnhem (1980-2012). Spring migration was seen between the end of March en the beginning of June and autumn migration between the beginning of August and the end of September (Figure 1/Figuur 1). Patterns in spring pinpoint to an advance in onset (10%) in migration, and a (weak) delay in the end (90%). In autumn the whole pattern has advanced. Data on onset and end as well as the median data (50%) in three periods are given in Table 1 (Tabel 1) and visualized in Figure 2. Data on first birds in spring (phenology Arnhem and migration counts) show an advance of fifteen days since 1980 (Figure 3). For the onset of sping migration the relation with time is not significant, whereas early years are concentrated in recent years (Figure 4). In autumn onset, median and end show an advance of fifteen days since 1978 (Figure 5). Data from observation site Amhem show a similar advance (Figure 6). The last House Martin on observation sites showed a significant delay since 1978 (Figure 5). Since changes in timing of arrival, migration and departure might be linked with climate change, data are linked to temperature. In spring the date of the first observation (Figure 7) the onset (10%) and 25% are negatively correlated with the temperature between 15 March and 30 April. Median and end dates (90%) show no correlation with temperature. In autumn onset, median date and finish of migration show a negative correlation with the temperature during 15 March-31 May and 15 March-30 June (Figure 8). Temperature in late summer and autumn showed no correlation with the timing of the autumn migration. Therefore the timing of the autumn migration is linked with the arrival of birds on the breeding grounds and the onset of breeding as these are affected by spring temperatures. Those two elements are probably the main triggers for the timing of the autumn migration southward.