WORTELBOER R (2015) A closer look at Common Swifts Apus apus: results of ten years of nest monitoring with cameras. LIMOSA 88 (2): 57-73.
In 2003-2012, the Dutch Swift Society (GBN) installed cameras at nests of Common Swifts, with the aim of learning more about the swifts' breeding biology without disturbing their nests. In total 376 clutches were monitored, distributed over 43 villages and cities in the Netherlands (Fig. 1a). In the later years of the study more than 80 cameras were operational (Fig. 1b).
Arrival dates of first parents were relatively constant, varying between 17 and 30 April (Fig. 3a, Tab. 1). In some years (e.g. 2010) egg laying was postponed because of the cold weather (Fig. 3b). The shortest observed incubation period lasted 17 days; the average length was 21 days (Fig. 4a). The nestling period lasted on average 42 days, with no differences between successive young, but with considerable variation (Fig. 4b). The times of first flight of the young Swifts showed a daily pattern with a preference for fledging in the dusk (Fig. 5).
The average numbers per clutch of eggs, nestlings and fledged young were 2.46, 1.99 and 1.79, respectively (Tab. 1). These numbers were higher in clutches started early in
the breeding season (Tab. 2). On average, 80% of clutches successfully raised young until fledging (Fig. 6). Replacement clutches increased this proportion to 90%. Breeding success
in natural nest sites was on average 15% lower than that in artificial sites (nest boxes and special roof tiles with an entrance for Swifts, Tab. 3).
Average breeding success over all clutches showed no relation to mean temperature, hours of sunshine andduration of precipitation when using yearly mean values (Fig. 7). However, when using data of individual clutches and local weather during the exact nesting periods, multiple linear regression showed significant effects of weather conditions on number of young fledged, egg survival, nestling survival and proportion of successful clutches (Tab. 4, Fig. 8).
Temperature was the dominant factor showing suboptimal responses at both low and high temperatures, especially in natural nest sites. This might indicate unfavourable
conditions for the young in nests in natural nest sites in warm summers.
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