Once you have found a good habitat one has to think about other life challenges, predators and rivals, to name a few. For a third year, the Polish aggregate producer Górażdże and OTOP\BirdLife Poland work together on a number of wetlands in Southern Poland to improve local populations of Black-headed and Mediterranean gulls and Common Terns. Tomasz Wilk reports from the field.
Tomasz: The beginning of the project was smooth and easy. Following our planning meeting we bought the necessary equipment. The electric fence we wanted to install before the breeding season starts.
The first difficulty came when we saw the gulls were not interested with the island where we planned to put the fence on (the one where we prepared the habitat by removing the bushes 2 years ago). This was probably due to the presence of the predator at the beginning of the breeding period, but we cannot be 100% sure what the reason was.
Anyway, had to shift to the smaller island, where we could see the birds were forming the colony so we installed the fence. So far, so good.
The fence was working, birds started breeding and no signs of predation in the colony were observed. But then, heavy rains came to Southern Poland and the water level in the Nyskie Reservoir started rising. The island was partially flooded, only ca 60% of its area remained above the water level, and the fence was flooded. During this period the predators attacked the colony and killed ca. 30 adult Black- headed gulls.
We have moved the fence out of water to protect the rest of the colony (the fence is still in working order because key elements were not flooded). The water level should go down from now on, so we expect the situation will stabilize.
Quite an adventurous project as you can see.
Predation is considered one the main threats for colonially nesting water birds and it has been also proved as a key threat in the Polish context. The core predators in gulls and terns colonies are mammals, mainly red fox and American mink Neovison vison, whose numbers have increased significantly in recent decades in Poland.
Nyskie Reservoir is in some years the most important breeding colony of Black-headed Gull and Common Tern in the whole Lower Silesia region, and one the most important breeding sites for Mediterranean Gull in Poland. The biggest island, where the project activities are focusing (and where the vegetation removal took place in 2015) is the single most important colony in the reservoir. As it is the largest island, its role is especially highlighted during high water levels, when smaller islands are flooded. Strong predation in this location therefore affects site of high, regional importance for breeding birds, and any activities aiming at ensuring high breeding success on the island should be viewed as having not only local, but wider, regional impact. The main aim of the project is therefore to minimize the pressure of mammalian predators in the largest colony of gulls and terns in Nyskie Reseirvor. This will complement the previous activities on that island (OTOP/Górażdże project), focusing at improving habitat quality by vegetation removal.
For the geeks here, technical parameters of the fence:
- height: 0.5 m
- perimeter: ca. 350m (7 x 50 m)
- eye: ca. 5×5 cm
- material: chrome-nickel wires + plastic coating
- power supply: accumulator 12V/75Ah + solar panel