Aspects of the breeding biology of a swallow (Hirundo rustica) population

• Main Author: Wellbourn, Melissa Jean
• Published: University of Manchester 1993
• Subjects: 598.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601490

During this study, various aspects of the breeding biology of the Swallow (Hirundo rustica) were investigated. Firstly, factors which affected the reproductive success of individuals in the population were examined. First brood clutch size was unrelated to laying date. The size of the second clutch was significantly affected by laying date, such that the later a second clutch, the smaller its size. The size of the second clutch was independently related to first brood laying date; when compared with those which had earlier first broods, late pairs had smaller second broods. Pairs which had only one brood laid significantly later than the first brood of pairs which laid more than one. The earlier breeders laid most eggs during the breeding season. Males and females differed significantly in only one biometric measurement, that of tail length. Males with breeding experience had longer tails and earlier first clutches than those with no breeding experience. One measure of tail length was significantly longer in females with breeding experience. These birds also had significantly higher body weights than their inexperienced counterparts. Females with breeding experience laid second broods slgnificantly earlier due to the shorter interval between fledging their first brood and laying the second clutch. Fledging success was highest on two pair farms where the birds were more likely to have a second brood. Secondly, instances of "strange" swallows appearing at occupied nests were discussed in the light of four hypotheses which have been postulated by other researchers to explain similar occurrences of this type of behaviour in the Swallow and other species.Visits are classed as attempted infanticide, helping, prospecting and interaction with neighbours. Visits by Swallows, in this study, which included aggressive interactions between "strangers" and nestlings, i.e.; attacking nestlings and the destruction of eggs, were deemed as infanticide. Visits when no interactions were observed, but when the visitor was a recent fledgling were defined as "prospecting". Juveniles and adults, which visit nests in the period before migration, may aid their future reproductive success by assessing the quality of breeding sites. Infanticide was a rare occurrence in this population probably because there were no unmated males. There were no helpers, probably due to the large number of available nest-sites and the roughly equal sex ratios. Neighbours may visit other nests during the breeding season for similar reasons. Thirdly, behaviour during feeding visits was examined. Adults were found to be allocating food at random among the nestlings. For nestlings, begging first was found to be the biggest predictor of obtaining food. The rank, by weight, of the nestlings was found to have no effect on their ability to acquire food. When the nestlings were small, adults alerted them to a feeding visit by the use of contact calls after they had landed on the nest As chicks got older, parents phased out contact calls and the nestlings started begging before the adults landed on the nest Fourthly, genetic paternity and maternity was determined using DNA fingerprinting on a sample of 39 families. In the population, extra-pair offspring were rare (3.4%), and intra-specific brood parasitism was found only once (0.3%). In the 5 cases in which paternity of the mis-matching offspring could be attributed, the genetic father was found to be breeding within 100m. In the 5 instances of mis-matching offspring which could not be attributed to any of the males breeding locally: these probably resulted from opportunistic extra-pair copulations involving males not breeding in the area. This study has tried to establish which effect the breeding success of the Swallows in this study. There is little, if any, comparable data from other studies of this species. In order to more thoroughly asses the theoretical significance, a longer study would need to be undertaken. This study has provided additional, anecdotal, evidence that Swallows engage in, at first glance, "abnormal" behaviours during the breeding season, for example; an adult was observed to attack nestlings on several occasions. Such events are rare, in both this and other studies, and it was not possible to reach definite conclusions relating to the occurrence of such behaviours. The single year's observations on the distribution of food to the nestlings was unable to address the underlying causes of behaviour but it did provide tantalising glimpses of possible explanations. The paternity survey carried out in this study has added to the body of evidence that extra-pair copulations do occur in this species. Features of adult birds, their habitat and breeding behaviour were related to the occurrence mis-matching offspring. These relationships have suggested further studies which could elucidate the factors driving individuals to engage in extra-pair copulation sas a complementary breeding strategy.