The breeding biology and causes of nest failure of Scottish Black‐throated Divers Gavia arctica

• Published in: Ibis
• Main Authors: MUDGE, G. P., TALBOT, T. R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1993
• Subjects: Sutherland; Gavia arctica
• Online Access: http://dx.doi.org/10.1111/j.1474-919x.1993.tb02822.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1474-919X.1993.tb02822.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1474-919X.1993.tb02822.x

The breeding biology and causes of nest failure were examined for Black‐throated Divers Gavia arctica in core areas of their Scottish breeding range in 1983–1987. Breeding was confirmed for up to 88% of territorial pairs each year ( n = 28–62), and 76% of nests were on islands. Hatching success was consistently low with, on average, only 43% of territorial pairs managing to hatch a clutch each year; 64% of recorded nest failures occurred during the first week of the 4‐week incubation period. Overall breeding success in West Sutherland in 1984–1987 averaged 0.23 chicks per territorial pair per year, while in Ross‐shire for 1986–1987 it was 0.29. Forty percent of hatched chicks survived to fledge, and 92% of recorded deaths occurred in the first fortnight after hatching; 4.8% of fledged broods held two chicks. Causes of nest failure were assessed with the aid of surveillance cameras. Approximately 30% of losses were due to water level changes (mostly floods), 48% to predators (primarily nocturnal mammals, but also Hooded Crows Corvus corone ), 13% to human egg collectors and 5% to desertion following human disturbance. Scottish Black‐throated Divers produce only half the number of chicks tentatively estimated to be required to maintain a stable population. The main difference between the Scottish and more successful Swedish populations is in the degree of chick mortality.