The largest breeding colony of Mediterranean Gulls Ichthyaetus melanocephalus in a gravel-pit in Bieńkowice in the valley of the upper Odra river in 2018
At the turn of April and May 2018, in the active gravel-pit in Bieńkowice (Krzyżanowice commune, Racibórz district, Silesia voivodship) in the valley of the upper Odra river, we have observed large concentrations of adult of Mediterranean Gulls Ichthyaetus melanocephalus in the breeding colony of Black-headed Chroicocephalus ridibundus. On 25 April we saw 19 individuals at the same time, some of which might have been breeding birds. However, the relatively high herbaceous vegetation on the island with a breeding colony made it impossible to accurately calculate and clearly determine the status of the Mediterranean Gulls present there using only a telescope. At the same time we were informed that in the most important Silesian breeding colonies of this species – on the Reservoir Mietkowski and the Reservoir Nysa, the numbers are surprisingly low this year (oscillating within the limits of several breeding pairs). It was even more important to determine the situation in the new position.On 9 May, using the drone Phantom 4 Pro , navigated by Marcin Karetta, we managed to take a number of photos of the whole island’s surface from a height of 10 meters and 30 meters. Detailed analysis of all the photographs showed the simultaneous presence 56 of Mediterranean Gulls (including 54 birds after the third and third year of life and two birds in the second year of life). Among the photographed birds, 44 managed to confirm sitting on the nests. These were birds, which in the picture took a clear sitting position and were most often surrounded by a “garland” of dry plants constituting the nest building material. At birds in the clumps of high grass vegetation had no visible nest material, but the situation that they were resting, non-sessing birds was considered unlikely in such an environment. In a dozen or so birds (13-14), the moment of turning the eggs was captured in the picture, which allowed to confirm the breeding.
Photo 1. View at the part of the island with a colony of Mediterranean Gulls Ichthyaetus melanocephalus in Bieńkowice, April 2018.
Photo 2. Aerial picture of the island with a nesting colony of Mediterranean Gulls, Black-headed
Gulls and Common Terns in Bieńkowice, viewed from a drone
12 individuals, that were considered non-breeding or whose breeding was in doubt, standing next to birds sitting or sleeping without clear signs of sitting. Two birds were also seen in the second year of life, which behaved like a pair (turning), but probably did not take part in the breeding. The breeding population of the Mediterranean Gulls at this site was estimated at least 44 breeding pairs. In addition, thanks to the photos from the drone, the information was obtained that on that day on the island also nested 2874 pairs of Black-headed and 244 pairs of river terns Sterna hirundo. Their breeding status was assessed similarly as in the case of Mediterranean Gulls, but for river terns the criterion of the presence of nesting material, which most often, from the drone’s perspective, was not visible at all, was not applied.
On 26 May, 1 June, 6 June and 11 June, with the help of Maciej Gajewski (1 June) and Jacek Betlei (6 June), we sailed to the island in order to directly control the state of settlement, ring nestlings and adult birds and read the rings. During the first inspection in the colony, it was possible to find directly about 25 still-nested of Mediterranean Gulls and nine abandoned (cold egg shells or extended eggs outside the nest or dead chicks in the nest itself). Many clearly killed nestlings were found then, probably by a terrestrial predator. About ten dead nestlings of different ages were found outside the nests, whose exact location on the island could not be confirmed by this. Each subsequent control of the island showed less and less active and more and more abandoned nests and dead nestlings of all species nesting here. However, as a result of these inspections, three new nests were found, which were not seen during the first visit to the colony. Direct controls confirmed the presence of at least 40 nests, which additionally gives credibility to the result obtained with the use of photos from the drone.
Direct controls confirmed the presence of at least 40 nests, which additionally gives credibility to the result obtained with the use of photos from the drone. From that moment, due to the intense penetration of the island by predatory mammals, the colony of Mediterranean Gulls quickly disappeared. Probably all the chicks were killed, and adult birds left the nest. A similar fate happened to the whole population of the river tern. Until the end of June only some pairs of Black-headed stock remained, in which the breeding success (several dozen volatile youngsters) has been demonstrated.
During the visits to the colony, 22 of Mediterranean Gulls (13 nestlings and 9 birds in their third or third year of age) were ringed with red plastic rings. Out of the four ringed adult individuals, return information was obtained by the end of November 2018. Three of them were read over the English Channel in France and one in southern Portugal. Among the breeding 22 of Mediterranean Gulls in the colony in Bieńkowice nine rings were read – 5 Polish, 2 Czech, one Danish and one Belgian. An interesting fact was the simultaneous presence in the colony in Bieńkowice of a bird ringed as a breeding bird in 2011 on the Nysa Reservoir and the then ringed nestling from its breeding.
Photo 4.Drone picture of a part of the island inhabited by gulls. Incubated nests of Mediterranean Gulls are marked in red
Photo 5. A part of a colony photographed from an altitude of 10 m. Incubating individuals were easily identified to the species level from this distance
The island where the described broods were found is located in the southern part of the 50 ha post-excavation reservoir. It has an area of about 1.8 ha and was created around 2015 by the owners of the gravel pit to provide a nesting place for birds. In the first two years there were no breeding trials, and Black-headed and river tern nested (120 and 58 pairs respectively) on two smaller islands in another part of the gravel pit. It was not until spring 2017, when the previously occupied sites were washed away by water and overgrown with tears, that the birds settled on the large island described here in the south-western part of the gravel pit. At that time, at least 120 couples of Black-headed and 68 couples of river tern were found. However, the birds were counted then only on the western part of the island, using a telescope from a distance of about 300 m, so it was certainly only a small fraction of the real population. In the colony one third year old of Mediterranean Gulls was seen, but it did not behave like a breeding bird. However, the entire surface of the island was not controlled by the drone, nor was the direct control of the colony, which means that the actual condition of its settlement by black-headed gulls in 2017 is unknown. However, the entire surface of the island was not controlled by the drone, nor was the direct control of the colony, which means that the actual condition of its settlement by Mediterranean Gulls in 2017 is unknown. The Mediterranean Gulls is a relatively new breeding species in the Polish avifauna. It started to nest here in 1981, and since 1991 its population has been gradually growing. In 2007, the number reached 96 breeding pairs and has since fluctuated between 55 and 97 pairs. In recent years, the species inhabits the most south of the country, especially Silesia, which brings together 55-65% of the population (Stawarczyk and others 2017). In 2018, at least 88 breeding pairs of Mediterranean Gulls nested throughout Poland (P. Zielinski – non-public information), which means that the colony in Bieńkowice focused this year half of the national population of the species. The number of pairs reached by us equals the entire national population in the very weak season of 2017, when exactly 44 pairs were recorded in Poland (Chodkiewicz and others 2018). The colony of 44 pairs described here is the largest breeding cluster described so far from Poland. Slightly lower number – 42 breeding pairs were recorded in 2014 on the Mietkowski Reservoir (Stawarczyk and others 2017). In the next breeding season, we plan to continue monitoring this breeding site using a drone, which is currently the most effective, efficient and least invasive method of counting colony nesting birds (Zbyryt 2018). In case of obtaining the consent of the owners of the gravel pit we want to introduce active protection of the colony, especially by preventing predation of mammals. Thanks We would like to thank Alas Utex Sp. z o. o. for allowing us to conduct research in the gravel pit. We thank Marcin Karetta for help in counting the nests of Mediterranean Gulls with the help of a drone, as well as Maciej Gajewski and Jacek Betlei for valuable comments and support in the control of nests and the capture of breeding birds.
In 2018 the largest Polish colony of the Mediterranean Gull was found in a gravel-pit located in Bieńkowice in the valley of the upper Odra river (the southern part of Upper Silesia). Drone photos suggested that the colony hosted at least 44 occupied nests. Furthermore, one photography showed 56 adult individuals of the species. The total Polish population of the Mediterranean Gull has been estimated in recent years at 44-97 breeding pairs. In 2018 at least 88 pairs of the species nested in Poland, so the focal population hosted 50% of the national population. Until recently, before the colony in Bieńkowice was found, the largest breeding colony of the species (42 pairs) had been described from the Mietkowski Reservoir.
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