The Breeding of the Starling Sturnus Vulgaris in Relation to Its Food Supply

Abstract

Summary. The relation between a population of Starlings and its food supply during the breeding season was investigated at Craibstone, near Aberdeen, during 1950, 1951 and 1952. In a square mile, including Craibstone, the number of breeding females increased from 43 in 1950 to 52–54 in 1951, and to 78 in 1952. During the breeding season the Starlings obtained most of their food in the upper layer of the soil in pasture fields. Leatherjackets (Tipula sp. larvae) were the most important, and the seasonal variation in their biomass was measured. The period of availability is long, but that of great biomass is short. Earthworms were abundant in the soil, but formed a small proportion of the food taken. Synchrony of laying the first clutches is marked; in second clutches (common at Craibstone in each year) it is less pronounced and is derived from that of the earlier layin. Starlings fed from a limited number of feeding areas. The food brought to the nestlings was studied in part by high‐speed Hash photography. On the average leatherjackets formed over 80% of the food brought to the nestlings and earthworms 16%. The weight of, and variation in, individual feeds were calculated. There is a marked peak of feeding activity in the early morning, often with a lesser peak in the afternoon. Earthworms tend to be brought early in the morning. The proportions of different items do not vary seasonally. The relation between feeding rate and the amount of food brought is not constant. Owing to individual differences in the feeding activity of parents and the response of the young, the amount of food required to rear a brood cannot be estimated. The proportion of available leatherjackets consumed by nestlings was about 1·9% in 1951 and 7% in 1952. The mean clutch‐size was similar in each year, and second clutches were smaller than first. Nestling weights did not differ significantly between broods of different sizes or in relation to the amount of food available. It was concluded that: The synchrony of first clutches may be due to the advantage of having successful second broods, and the evidence suggests that these are ultimately controlled by the date the leatherjackets emerge. The synchrony may also have survival value in providing the opportunity for gregarious feeding by the adults and, later, the juveniles. The occurrence of second broods appears to be determined by how early breeding starts and when the leather‐jackets disappear from the soil. Breeding‐rate and success were not closely related to the available food supply. There is much evidence to suggest that the available food‐supply is the ultimate factor timing the end of the breeding season, but it probably does not determine the onset of breeding. The density of the breeding population is not controlled by the food available during the breeding season.

Diet of StarlingSturnus vulgarisnestlings on farmland: the importance of Tipulidae larvae

“…This concurred with a range of previous studies (e.g. Dunnet 1955, Tinbergen 1981, Westerterp 1982, Wright et al 1998 and suggests that for our study populations below- ground prey, Tipulidae larvae in particular, form the majority of the diet of Starling nestlings. However, it should be noted that prey availability in our study areas was not measured and thus the patterns of provisioning we report may simply be a result of local prey abundance.…”

“…The data suggest that parents of older larger (4-6 nestlings) broods are unable to provision at the same rate per nestling as older smaller (1-3 nestlings) broods. the nest, these results suggest that given the opportunity adults would increase the provisioning of Tipulidae larvae with nestling age, as found in other studies (Dunnet 1955, Westerterp 1973, Tinbergen 1981. However, it seems likely that they are constrained by brood size (Fig.…”

“…reaches a plateau for Starlings at around day 10 and then decreases from day 15 onwards (Dunnet 1955, Westerterp 1973, Tinbergen 1981. Similarly, the effort required to feed larger broods means that parents are less likely to provision their young with prey that are difficult to access compared to those with smaller broods (Wright et al 1998).…”

“…However, soil-dwelling larval prey is usually taken most frequently (Feare 1984). Of these soil-dwelling prey, Tipulidae larvae have been found to be important in Holland (Kluijver 1933, Westerterp 1973, Tinbergen & Drent 1980, Tinbergen 1981, England (Wright & Cuthill 1990a,b, Wright et al 1998 and Scotland (Dunnet 1955), but their relative importance to farmland nesting Starlings has received little attention. Furthermore, although a number of studies have looked at the importance of Tipulidae larvae (see above), most were carried out more than 30 years ago, before the widespread spraying of grass fields to control dipteran larvae (Campbell & Cooke 1997, Garthwaite et al 1997.…”

“…Dunnet 1955) and variations in diet composition reflect the distribution of invertebrates on a regional and local scale (Feare 1984). Despite regional differences, provisioning adults make use of Coleopteran and Lepidopteran larvae in most areas worldwide (e.g.…”