Age and sex of Snowy Owls (Bubo scandiacus) during summer irruption on Beliy Island, Yamal in 2015.

Abstract

In early summer 2015 a super peak of lemmings (Lemmus sibiricus) appeared on Beliy Island north of Yamal peninsula, Russia (73o19’N, 70o15’E). Considerable numbers of Snowy Owls (Bubo scandiacus) were present, possibly as a result of the abundance of lemmings. On 7, 9, 13, and 15 July a total of 69.7 km was covered on foot. Snowy owls were approached and 344 images of perching and flying birds were captured. At most 89 individual Snowy Owls were seen from one vantage point. Images were sorted by number, time and date recorded on the image files. Images suitable to sex and age the owls were treated in Photoshop to enhance details of molt and bar patterns in wings. The birds were aged analyzing molt patterns, and individuals were recognized by bar and molt patterns in their wings. Eleven males and 14 females were aged, of which 14 (56%) were second calendar year (2CY) birds hatched in 2014. Six owls were in their second or third wing feather molt, thus classified as 3CY-4CY birds, while only five were birds with no juvenile flight feathers left (5CY+). Several individuals only photographed perching on the ground appeared to be juvenile 2CY birds, but these were not included in the sample due to lower certainty of identifying individuals and aging perched birds from images. Although two nesting pairs were recorded, the majority of the Snowy Owls on Beliy Island in July 2015 were young, presumably non-breeding birds. This study shows that photographying as many Snowy Owls as possible during an irruption may reveal the age and sex distribution of the birds present.