AVIS-IBIS

Birds of Indian Subcontinent

Seasonal Changes in Flocking Behavior of Starlings as Correlated with Gonadal Development

Publication Type:Journal Article
Year of Publication:1970
Authors:G. Davis, J
Journal:The Wilson Bulletin
Volume:82
Issue:4
Date Published:1970
ISBN Number:00435643
Keywords:Sturnidae, Sturnus, Sturnus vulgaris
Abstract:1) Starling populations in west-central Illinois dropped to one of its lowest levels of the year in July 1965 (100 birds per 100 miles of census route) as a result of either young Starlings migrating northward or the postjuvenal molt making the Starlings less active flyers and less conspicuous to the observer. 2) The initial stages of migration were observed in August as the average flock size increased from 2.5 birds per unit to over 8 birds per unit. From this time the Starlings began to accumulate until populations reached a peak of over 800 Starlings per 100 miles of census route during the period 26 September through 2 October. 3) The migration from further north of young Starlings through west-central Illinois after the adults already had migrated through was thought to be the cause of a second peak in the population to nearly 800 birds per 100 miles of census route in late October. 4) Starling populations gradually declined over the winter from 250 birds per 100 miles to about 100 birds per 100 miles of census route as a result of "weather movements." 5) In late February the average flock size decreased from 6.5 to 2.5 birds per unit as some Starlings began showing an interest in potential nest sites. 6) Spring migration into west-central Illinois which began in the first week of March did not exhibit the large flocking tendency of fall migration and it occurred over a longer period of time. 7) During the nesting season the numbers of Starlings observed along the census routes were low, about 100 birds per 100 miles of census route, because the adults were confined to the vicinity of the nest by nesting activities. The numbers along the census routes did not increase again until June when the fledged young formed into juvenile flocks, and the counts rose to near 300 birds per 100 miles of census route. 8) The flocking of Starlings was of two distinct types: during August through January, there was a tendency to gather into large flocks and during February through July, there was a tendency to occur only in pairs. It is believed that the tendency to flock among Starlings is inhibited by the level of sex hormones in the blood.
URL:http://www.jstor.org/stable/4160010
Short Title:The Wilson Bulletin
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