Some short notes on Short-toed Eagles in Northern Ukraine in 2014

• The high availability of prey

Judging by all, the past year was really rich in prey for Raptors at all, and rich in reptiles for Short-toed Eagles in particular. That was expressed not only in relatively more frequent records of Grass Snakes (Natrix natrix) and lizards at the usual eagles’ hunting grounds, but also in some indirect signs. The weather was mild, without notably long hot and rainy periods. Short-toed Eagles of different pairs were back with prey at their nests after departure to the hunt sooner than usually. Hunting for snakes was highly efficient. Looking for prey and catching it took less time and the eagles allowed themselves to spend hours for roosting, flying or even playing air games at the breeding sites. That all indicated that the breeding success would be high (Data on breeding of Short-toed Eagle in Northern Ukraine, XLS file with formulas).

• Earlier leaving nests and the departure

The earliest leaving nest by juvenile Short-toed Eagle was recorded this year. It was on August 9th. That day a juvenile Short-toed Eagle was already perching not on the nesting tree (like in 2009), but at a distance of about 100 m from it (Findings of the eagles in the Chernihiv Polissya). Also other juveniles left the nesting sites sooner in comparison with previous years, probably, as a result of good uninterrupted feeding. The latest date of observations of Short-toed Eagle at their home ranges in Northern Ukraine this year was September 13th. One of pairs with the juvenile had departed from the breeding site a week or two earlier than in 2013. It looks like a readiness of the juveniles to accompany their parents in migratory journey determines the beginning of their autumn migration as well as of the adults’ one. Parents expect when their eaglets reach the above-mentioned ability and this is the only thing that forces them to stay at the home ranges until the end of September.

• Conflicts with Ravens and Black Storks

For 2 controlled pairs of Short-toed Eagles the following behaviour was observed. The STEs regularly attacked Black Storks (Ciconia nigra) and Ravens (Corvus corax) which were approaching the eagles’ breeding sites. One of the mentioned pair chased Storks, other Ravens. Those birds were quite numerous at the home ranges of both pairs. But Ravens behaved aggressive and, probably, the STE female accompanied her partner with prey bought for their chick to protect him from ravens’ attacks in the vicinity of the nest (Short-toed Eagles in flight. Northern Ukraine. 2014). When the male chased Ravens it reminded games whereas the female was serious, she rushed at the Raven with loud alarm cries and the bird could be harmed in a case of being overtaken. Chases of Storks by the other pair were performed like typical following after Short-toed Eagles the intruders in the course of intraspecific territorial conflicts (the B11 STE in the photos).

• Aerial games at the breeding site

Aerial games of male and female Short-toed Eagles of one pair while their feathered chick was in the eyrie were observed for the first time. Probably, this behaviour was associated with the same high availability of prey during the season. In 2008 such flights were performed in August by a pair without a chick which would need to be fed. The flights are imitations of attacks when both partners rush at each other aiming the talons forward. At the start, the partners slowly circle and hover on curved wings at times with lowered legs, then rapidly close approach to, but don’t grasp each other. When doing this sometimes the male turns out above the female, sometimes she does. Soon the eagles fly away again and continue the slow flight. On 20th July 2014 the partners were performing such movements at the breeding site within 5 minutes.

• Building a nest on June for the next season

In June a pair of Short-toed Eagle whose breeding had been interrupted were observed in the evening in a joint flight at a region of their traditional breeding sites of 2006-2014 years. The male had recently risen from somewhere with a tree branch in his beak. The branch had green leaves notable from a distance. The eagle circled and hovered over the forest; his partner, big old female, kept not far from him. Then the male took the branch into his talons and both the partners headed for their old breeding site that is located farther from the forest’s border and hadn’t been occupied since 2009. That year this pair also used a nest which had been built yet a year before. This should be checked out in 2015, but probably it was a case when Short-toed Eagles build a nest for the next breeding season aiming to not waste valuable time of it.

• Treatment of nesting trees with turpentine against Martens

The treatment of 2 nesting trees with turpentine was done with a goal to protect the chicks of Short-toed Eagles from possible attacks of Martens (Martes martes). The nesting trees and neighbour ones were treated in the beginning of July when the chicks were too small yet to attract the attention of Martens by movement and voice. Eventually, the both juvenile Short-toed Eagles have left the nests successfully. The method is described well on a film about the conservation of the Greater Spotted Eagle in Poland «The Greater Spotted Eagle – a bird like no other» by Ireneusz Chojnacki. In Northern Ukraine 1 liter of turpentine was used for the treatment of trees at 1 breeding site. A part of each tree trunk at a height of 1-1.5 meters above the ground was sprayed with the substance around the entire circumference. After that the surface of the trunks were smelling during at least 2 months. Certainly, Martens felt it stronger. Both times we approached to the nesting trees early in the morning and managed to not disturb the owners of the nests, but it was difficult indeed at that period and it is difficult to recommend something to avoid the disturbance. Obviously, the action cannot be conducted when it rains or if there is a chance that the rain will begin, to avoid the risk of the chick’s death due to the hypothermia. We must admit that when eaglets are very young the mere treatment of nesting trees is risky and should be done only if the danger of Martens’ attacks is real.

• The shortest period between replacements of flight feathers and the longest use of the same nest

A replacement of the same big flight feathers after less than 1 year of wearing (the L11 bird in the photos) was observed for the first time (Replacement of the biggest 14 flight feathers). Distinct defects of the same feathers regularly appear probably because of using the same nest and perches by the Short-toed Eagle female. As the result her wings regularly stumble on the same obstacles and the feathers are damaged on them. This pair occupied the nest for the 4th year running. Thus, this is the longest use of the same eyrie within 11 years of the monitoring in Northern Ukraine. On the other hand, the defects could appear because of certain individual habits of certain birds not only at their breeding sites. Thanks to presence of those defects and their changes the following inter-replacement periods were determined: at most 9 months for both the 6th primaries; 9 months for the left 5th one; 10 months for the right 9th primary and 11 months for the left one. Also the left 8th and right 9th primaries of another STE female (the A11 bird) were replaced with new ones after 12 months of wearing. Before that the shortest known intermoulting period was 13 months (B11), the longest one clearly determined also by a presence of a significant defect is 22 months (A11) and the longest one uninterrupted with a high probability is 27 months (L11). Such a large spread of values could be explained if it is supposed that Short-toed Eagles remove the defected feathers forcefully in periods of intensive moulting between migratory ones, whereas feathers in a good state could be worn within a couple of years.

• Territorial conflicts above sites of other pairs

Territorial conflicts when one, judging by all, adult Short-toed Eagle chased another one in an intermediate plumage over breeding sites occupied by other pairs of Short-toed Eagles were observed two times (Short-toed Eagles in flight. Northern Ukraine. 2014). Both times the owners of the breeding sites didn’t react anyhow. Although, they couldn’t miss the conflicts. It is still unclear why their aggressive behaviour wasn’t observed, as well as if the chasers were eagles of neighbour pairs well known to the owners or they were some wandering adult birds.
Please, view the related gallery of photos illustrating the notes; images of the same eagles taken in previous years are available as well.