Результаты первой попытки привлечения пары орлана-белохвоста в искусственное гнездовье

Abstract

The White-Tailed Sea Eagle (Haliaeetus albicilla) is a large bird of prey native to the Southern shore of Lake Balkhash. In 2021, a pair of White-Tailed Sea Eagles nested in a dry Poplar tree (Populus diversifolia) located 7.5–8 km southwest-south of the village of Karaoi, Balkash district, Almaty oblast, and raised two nestlings. The breeding territory was located in a transitional biome containing characteristics of wetlands closer to the Ile River delta and typical desert biotopes of the Southern Lake Balkhash. The nest was located in a cluster of poplar trees, only a few of which had relatively high height and trunk capacity, and only one of which was suitable for a large nest. The nest was annually rebuilt and successfully used for brooding by eagles for over 10 reproductive seasons. The breeding territory is located on “Duman-Ai” farm. There are no other poplar trees suitable for nesting within a 10 km radius of the nest. As a result of strong storm winds on July 8–9, 2021, the nest fell, together with the dry tree it was built on. However, by the end of June 2021, both fledglings had successfully fledged. In the spring of 2022, the nest and fallen poplar burned after several small fires were set in this location. Reed fires (often very extensive) and riparian fires (trees of various species of willow, Elaeagnus, and populus) along streams are common in the area, especially in early spring. As a result, riparian thickets have been in a severely depressed state for many decades, and in some places they are practically reduced to nothing, especially in the middle part of the Ile River delta. In the fall of 2021, with the assistance of the WWF Central Asia Program and cooperation with the Ile-Balkash State Nature Reserve, one of the authors of this publication constructed an artificial nest near the fallen tree using five vertically-placed logs and multiple cross-bars. A platform made of fallen dry branches and dead poplar twigs was installed in its upper part, imitating a similar nest structure. The height of the nesting platform itself was 5.5–5.8 m, which is no lower than the height of the original nest of this pair which fell. In 2022–2023, 12 birdhouses for small passerines were installed on the logs and cross-bars forming the structure. After the the structure was finished, monitoring of its use by different vertebrate species has been carried out almost monthly together with members of the ecological club consisting mainly of students from the Ulgili secondary school in Karaoy village. Monitoring of the artificial nest was also supported by the WWF Central Asia Program. The creation of such an artificial nest to attract a breeding pair of White-Tailed Sea Eagles was the first such endeavor in Kazakhstan, at least in the Southern shore of Lake Balkhash area. During 2021–2023, a pair of White-Tailed Sea Eagles from this breeding territory started to use it as a perch. In 2022–2023 Saxaul Sparrows (Passer ammodendri) nested repeatedly in the birdhouses installed in the structure, as well as in the branches of the artificial nest. Saxaul sparrows and Bukhara tit (Parus bokharensis) used the birdhouses for overnight stays in fall-winter and early spring. Afterwards, only Saxaul sparrows nested and hatched chicks in this site, including the 2023 season, having displaced the Bukhara tits. In neither 2022 nor 2023 did White-Tailed Sea Eagles nest on the platform. In September and October of 2022, the structure was frequently used by both individuals of the eagle pair for sleeping and resting, sometimes staying on it for many hours at a time. In late summer and fall of 2022, young eagle fledglings from this year were observed at this location, although it cannot be definitively stated that they were from this pair. In late January 2023, a pair was observed attempting to mate on the platform. The location of the platform within 150-200 m of a country road is clearly not conducive to nesting due to disturbance. The existing road is occasionally used by local fishermen, hunters, and small groups of people during the reed cutting season. Occasionally, vehicles attracted by this locally unusual object drove up to the nest (more often in 2021–2022 than in 2023), thus disturbing White-Tailed Sea Eagles sitting on the structure. Gunshots are heard in the area almost year-round. In the winter of 2022–2023, pieces of a cow carcass killed by wolves (Canis lupus) were placed on the nesting platform for the eagles. However, most of this meat was eventually consumed by Eastern Black Crows (Corvus corone orientalis) and Magpies (Pica pica). In late July – August 2023, the platform was used for resting and overnighting by adult White-Tailed Sea Eagles. Fledglings of this species were repeatedly observed at this location during the same period. It is possible that the local pair may have nested in a reed bed in the nearby lakes and channels of the wetland, the eastern boundary of which is located 400–500 m west of the nesting platform. Cases of eagle nesting on reed beds in this river delta have been described previously (Zhatkanbaev, 2011). Over the course of obsservations in late August and early September of 2023, no signs of nest construction were recorded, which could sometimes be observed in the fall in a number of birds of prey, including White-Tailed Sea Eagles. Measurements of another old massive nest of White-Tailed Sea Eagles on the left bank of the Naryn channel (Ile River delta), 12–13 km west-southwest of Karaoy village, which had fallen under its own weight, could be of interest. Another pair of White-Tailed Sea Eagles hatched nestlings there every year for at least 15–17 years. In 2022, one fledgeling successfully fledged from this nest. The nest and the live poplar tree on which it was built (trunk diameter at the base 35–38 cm, height to the lowermost branches of the crown 15.5–17.5 m) was found collapsed in March 2023, although in December 2022 it was still standing. It was clear that the primary reason for the fall was the extremely large mass of the nest, accumulated over many years of its constant renewal. Its weight, measured on August 25, 2023, in 23 separate parts using portable scales (accuracy to 0.05 kg) was 238.2 kg. The nest was 1.6–1.8 m in major diameter after the fall (excluding protruding branches and limbs), with the tamped-down mass of nesting material from previous years being at least 1.5–1.75 m high. The percentage of large branches was around 28–30%, some of them were 70–80 cm long, weighing up to 1.5–1.85 kg. Medium and especially small twigs, including those from the Saxaul and Indian Sparrow (Passer indicus) nests, made up the remaining 70–72% of the total nest mass. When the nest mass was dismantled, an unfertilized egg was found in the middle part of the nest, apparently covered over by the eagles many years ago during subsequent nest renewals.