Antonov A. & Atanasova D. (2003) Chick conditions in first and second broods in the Pallid Swift Apus pallidus. ARDEA 91 (2): 197-204

In 1999-2000 we investigated chick condition of first and second broods in the Pallid Swift Apus pallidus in Sofia city, Bulgaria. Data on nine variables characterising chick conditions were collected from post-hatching day 15 to fledging. First and second broods differed in the amount of mass loss. Second brood chicks lost twice as much weight (10.5 ± 3.05 g) as first brood chicks (5.5 ± 3.82 g). This difference is supposed to be due mainly to reduced fledging masses in second broods (39.7 ± 3.06 vs. 42.4 ± 5.36 g), since peak weights did not differ significantly. Chicks in second broods also reached their peak weights significantly later in the nestling period (34.2 ± 5.75 vs. 31.4 ± 5.12 d), and had significantly lower wing loading. Differences in wing loading probably reflect different selective pressures acting during immediate post-fledging periods in mid-summer and late autumn. Hatching asynchrony was more marked in second clutches and was reflected in more pronounced effects of brood hierarchy. Within second broods early hatched chicks had a longer nestling period, reached peak body mass significantly earlier, had longer slimming periods and fledged longer-winged than late-hatched siblings. None of the variables characterising chick condition differed significantly among siblings within first broods. This was supposed to be due to the more plentiful and stable food supply in summer when first broods are raised. Chicks growing in second broods with singletons were of poorer condition than both early hatched and late hatched chicks in second broods with two chicks