Steller’s sea eagle Haliaeetus pelagicus nest repair behavior is described based on observations made from 2007-2008 on north-eastern Sakhalin Island, Russia. Nest repair began in early March, immediately following the resident pair’s arrival from the wintering grounds, and took approximately three weeks to complete prior to egg incubation. Both the male and the female engaged in repair activities. The male played the predominant role in bringing material to the nest, and the female’s role was primarily to expand the platform and to shield it from precipitation. Much of the nest repair effort (up to 70%) occurred in the first half of the day from 05:30 to 12:00. Hard materials (branches 0.3 to 3.0 m in length) were collected within a radius from 30 to 250 m from the nest. Soft materials (such as lichens) were brought from a distance of 250 to 2500 m. These collection radii can be used as guidelines in nest searches, as a flying eagle with hard material typically indicates that a nest is close by. Repairs continued throughout the incubation period and when chicks were fed, however the frequency of materials brought to the nest was reduced 4.8 times during this period as compared with the pre-incubation stage. Up until the chicks were about 20-25 days old, mostly softer materials were brought to the nest, and later (during molt from first to second nest plumages), the focus again shifted to branches. Materials brought to the nest at the end of the nesting period appeared to be an educational exercise, and not associated with actual repair. It was not possible to establish a correlation between nest size and nest age, as nest growth rates from different years and different pairs varied greatly and unpredictably.

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