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Arctic Science 2000 - Crossing Borders: Science and Community
Whitehorse, Yukon, Canada, Sept 21-24 2000
American Association for the Advancement of Science & Yukon Science Institute

Ecological Mechanisms of Population Stability of some Species of Waterbirds in Different Habitats

The problem of stability of populations both in disturbed and undisturbed habitats is one of the most important questions of sustainable conservation in Northern Ecosystems. Different species of birds in different seasons react differently to unfavorable factors of the environment. In this research we give several examples of these mechanisms for the population of Wooper swans (Cygnus cygnus) in winter on the territory of the Kronotsky State Bioshere Reserve (Kamchatka, Russia) and two species of colonial waterbirds (Charadriformes): Black-headed gull (Larus ridibundus) and Black-winged stilt (Himantopus himantopus) in their nesting period in Western Siberia. The last species is globally rare and is included in the Red Book of Russia.

1. The main factor limiting the number Wooper swans wintering in Kamchatka is the number of available areas of unfrozen waterbodies, the second is quantity of available food. In Kamchatka, due to the great many thermal springs, the first factor is not important, but the second is extremely important, because thermal springs are not rich in edible algae. For the population of Kronotsky Reserve’s Wooper swans, the lake Kronotskoye, which is highly eutrophic, is a rich feeding waterbody. Nearly 7-8%, and, in the morning peak of activity, up to 10 %, of this population are at this location. About 70-90% of the time budget, and at morning more than 90%, is spent in feeding behaviour. At the same time, the unfrozen part of the lake is not large and is not protected against bad weather or other unfavorable factors. That is why more than a half of the swans, feeding on the lake in the daytime, overnight on the sea-coast 40 km away. Thus, the population of swans of Kronotsky Reserve remains high by separation of feeding and nesting habitats. The swans leave mostly to winter not far from the nesting area and begin their breeding before the rest, which is very important in the severe conditions of the Kamchatka peninsula.

2. In Charadriformes, nesting in colonies, the main limiting factor of population numbers is easy access to nesting territory. During the last 10 years in Western Siberia low water levels have been observed, and that is why reduction of waterbirds’ nesting grounds has occurred. Breeding success in these conditions increases in the case of more synchronous nesting.

Black-headed gulls inhabit the colony during a short period, its spread of intensity was significantly Gaussian with positive excess (Ex = 1,44±0,29; t = 5,065 > 3; n = 71). This means that the terms of nesting are under the process of further synchronization by natural selection. The distance between nests regressed exponentially (k = 4,1881±1,31778; X2 = 0,23592; n = 23; p < 0,05%). This means that self-regulation of size of individual territory exists with a reducing tendency. The larger the initial size of the territory, the quicker the reduction in the colony size, giving an opportunity for the new individuals to settle. Each nesting pair keeps its territory through interspecies aggressive behaviour. Possible stress during aggressive contacts is a reason for the reduction in territory size.

3. Predators often destroy Black stilts’ nests (which is not the case with Black-headed gulls). That is why stilts in the colony behave less noticeably than gulls. For example, intensity of territory contacts is less than with gulls. That is why smaller individual territories in stilts corresponds to linear law and is divided into 2 phases (k = -0,58 ± 0,18; X2= 3,95159; n = 11; p < 5%). Thus, self-regulation of territory size reduction in the stilt colony is absent. At the same time, intensity of populating is divided according to 2 waves, which corresponds to the terms to 2 phases of territory reduce (X2 = 1.50041; n = 11; p < 0,05%). Territory sizes are practically constant inside the second wave, meaning that they are suboptimal plots of the colony. According to our data, the predators more frequently destroy nests of the second wave of nesting than nests of the first wave. We conclude that under conditions of high predation, pressing synchronization of breeding is less important than defensive behaviour. The second wave of nesting is a type of population reserve, as the nests of the second wave are destroyed first. Probably these are individuals of the first breeding year. This example of the stilt is another population mechanism of resistance against unfavorable conditions — separation of the population reserve — which is described for some species of vertebrates. Thus, different species influenced by different environmental conditions show different mechanisms of population resistance. In order to take actions to preserve the populations of these species, we ought not only to remove unfavorable factors (sometimes, it is impossible in the conditions of highly development agriculture and industry, as we have in West Siberia), but to optimize these resistance mechanisms. For example, in our case of the Black-winged stilt, it is possible to attract birds with the help of models (stuffed animals) of nesting birds in the suboptimal habitats. In this way it is possible to synchronize dates of nesting in the colony and, as a result, to increase success of breeding among the nesting populations of birds.

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