White-tailed eagle nest residents

Submitted by Looduskalender EN on Mon, 19.03.2018 - 09:47
Autorid

Text Urmas Sellis (EOÜ, Eagle Club)

Images from LK forum  members

Translation Liis

Estonian text posted 18.03.2018

Body

Who then live in this nest? The answer might be – white-tailed eagles. But looking more precisely into the matter the nest owners are a white-tailed eagle pair. The one with the darker plumage and dark eyes is the female whom we met immediately after installing the camera (February 5th). According to the classical identification it might be said that the female is quite young (considering the eyes and the general colouring of the plumage). But the tail colouring points to a mature age. It is however not impossible that this bird has some kind of pigmentation deviation and the preponderance of dark colouring does not indicate youth? The female was suspicious towards the camera to start with and preferred rather to fly away from the foreign eye. In the beginning the apprehensive female  left the nest even when they were in the nest together with her brave partner, but soon she got used to the harmless gadget.

 

Tumedasilme emaslind

The dark-eyed female (Screencap by forum member Urmas)

The male has lighter eyes and a lighter plumage. From this his age can be set to at least six years, probably even more. The male appeared in camera view on February 6th and he did not worryr about the camera lens.

Isas- ja emaslinnu erinevus (ning sarnasus) on ehk sellel pildil hästi näha

The differences (and similarities) between the male and female are well visible in this image (screencap captured by forum member Lianaliesma)

I believe that the male here is our old acquaintance Sulev whom we watched (2009-2013) through the webcam in the same nesting territory. But this is not the final truth – we have not collected material for a genetic analysis and two white-tailed eagles may be similar until confusion. The earlier webcam did not have the high quality of the present which means that a comparison of images is somewhat difficult. The dark patches on the tail are quite similar although not exactly identical. If this is Sulev then his tail feathers have changed meanwhile and the new feathers need not have exactly the same pattern, although a similar one. In addition all coloured feathers are worn down with time into lighter colour until they are changed to new ones, as a rule darker. When the images are compared then photos of the tail from 2010 differ most strongly. It seems that there is one more feather with a dark tip than in later images. The pattern of the other tail feathers is very similar. On the images from 2013 and 2018 the tail patches are almost identical.

Sulevi sabamuster 2010

Sulev’s tail pattern 2010 (composition by forum member Hali)

Sulevi sabamuster 2013

Sulev’s tail pattern 2013 (screencap captured by forum member Lõvi)

Isaslinnu sabamuster 2018

The male bird’s tail pattern 2018 (screencap captured by forum member Laranjeiras)

The likelyhood that a male bird very similar to Sulev would happen to come to precisely the same territory is rather small and this encourages me to think that he is Sulev.

It is worthwhile to observe the tail patches and to collect corresponding images of the different birds. From ringed birds (and also from the familiar camera eagles) we may after a number of years have enough data for someone to study them statistically. Without web cameras it would have been difficult to get images of the tail patches.

Untypically the birds in this white-tailed eagle pair do not differ particularly much with regard to size, the beaks too have quite similar shapes. The size of the birds can be estimated only when they are at exactly the same distance from the camera, otherwise there is a slight distortion from the lens that  depends on the distance. Because of this we initially believed the dark-eyed individual to be the male and the light-eyed one the female. Although both like to keep the nest hollow warm the dark-eyed female will lay the eggs … if it comes to egg-laying. We will see in the next few days.