Breeding biology of the Common Swift (Apus apus) in Ireland – the most north-westerly edge of the nesting habitat

Abstract

Ireland is at the north-western edge of the Common Swifts’ (Apus apus) range, and information on the basic breeding parameters of the species in this region is sparse. Therefore, the main objective of this research was to provide a detailed study of the breeding biology of the Common Swift in Ireland using information gathered at two artificial nest colonies located in Castlebar, County Mayo, and Maguiresbridge in County Fermanagh. Quantitative analysis was carried out on aspects of the breeding biology of the Common Swift such as a) important dates during the breeding season, including arrival, egg laying, hatching, fledging and departure; b) the colonies’ productivity and chick mortality in the nest; c) the chicks’ feeding frequencies; and d) egg loss during the incubation period. In addition, some aspects of the breeding biology were measured for their response to environmental factors such as rainfall, temperature and wind. The design of this research was based on the use of artificial nest boxes fitted with cameras connected to recording equipment, which resulted in the analysis of 28,500 hours of footage. During this investigation a total of 128 breeding attempts were studied which included observations of 300 laid eggs, 244 fledged chicks, 39 egg ejections and 17 chick mortalities. The phenological breeding cycle of the Common Swift is rigid, and there is a little variation in the values of mean arrival, egg-laying, hatching, fledging and departure dates each year. The average clutch size in Castlebar was 2.33 (se± 0.07) and 2.41 (se± 0.65) in Maguiresbridge. The average brood size in Castlebar was 1.53 (se± 0.16) and 2.28 (se± 0.08) in Maguiresbridge. The average number of fledglings in Castlebar was 1.38 (se± 0.15) and 2.13 (se± 0.09) in Maguiresbridge. A low average brood size and number of fledglings in Castlebar were the result of significant egg loss during incubation, a phenomenon apparently accentuated by the smaller size of the nest cavity along with small and shallow nest moulds. The total number of chick-feeding visits to the nest during the entire chick-rearing period was dependant on the size of the brood but the relationship was not linear. On average: broods of one were fed 501.28 (se± 20.15) times in the season; broods of two were fed 746.80 (se± 18.15) times; and broods of three were fed 872.5 (se± 20.15) times. Daily patterns of chick-feeding frequencies were related to the brood's size and age. For broods of one, the feeding remained constant throughout the period and reduced only in the last ten days before fledging. For broods of two and three, feeding increased linearly during the first eight to ten days following hatching and dropped during the last ten days before fledging. Weather factors influenced the daily number of feeds, with wind having the most positive impact, and to a lesser extent temperature (positive) and rainfall (negative). Egg loss for the most part was accidental with the adult swift knocking out the incubated egg. At both nest box projects; the size of the nest mould and the nest box was crucial in either influencing (Castlebar) or limiting (Maguiresbridge) egg loss. The presence of artificial nest moulds at both colonies appeared to influence poor nest construction, and in some breeding attempts led to a disregard for nest material collection. Overall, the findings of this study indicate that the Common Swift is well adapted to breed in Ireland, and if given suitable nest opportunities, it can produce sustainable colonies.