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Site parameters' variance - a missing dimension in the studies of nest-site selection?

Skórka P., Martyka R., Wójcik J., Lenda M.

Polish Journal of Ecology

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2011

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Vol. 59, nr 2

423-426

EN

In most studies of nest-site selection the data of habitat parameters are treated with analysis of variance. A basic assumption of this test is the homogeneity of variance. Here, we show that the nest-site selection process leads to lower variance of the selected parameters than in the case of random points which generally describe the available average characteristics of the environment. Thus, the variance should be accounted for in studies on nest-site selection and it should be treated not as a problem (as it is usually done), but as a source of additional important information on the selection process. Comparison only of mean values often does not lead to significant differences between nest site parameters and random points which may result from a small effect size (when animals select features similar to the general mean of available characteristics). Deeper insight into variance of the site parameters may elicit important results. We illustrate this issue with real data on nest site (islets and shores of water reservoirs) selection in the Common Gull Larus canus. Four (islet's area, vegetation height on islets, vegetation cover on shore and distance to nearest shrub or tree on shore) from eight parameters were favored by the birds and, as predicted, their variance values were lower than of those not selected (vegetation cover on islets, distance of the islets to shoreline, vegetation height on shore and distance to water).

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Segregation in sympatrically nesting red-winged starling Onychognathus Morio (L.) and European Starling Sturnus Vulgaris L.

Kopij G.

Polish Journal of Ecology

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2009

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Vol. 57, nr 3

589-595

EN

If two related species come into contact, it could be expected that, in order to coexist, they will either shift their niches apart from each other or one species will replace the other in the course of ever growing competition. Recently, two starling species, the indigenous Red-winged Starling and the exotic European Starling, came into contact in some places in Lesotho (southern Africa). In this paper, some breeding parameters of these species have been compared in an area of their co-occurrence. Studies were carried out in an urbanised habitat in Lesotho, in four consecutive breeding seasons (August-March) during the years 1998-2001. The average density of the Redwinged Starling was 13.8 pairs 100 ha[^-1], while that of the European Starling was 9.3 pairs 100 ha[^-1]. The proportion of the Red-winged Starling to European Starling breeding pairs (1.0:0.7) was strikingly constant over the four consecutive breeding seasons. Most Red-winged Starling breeding territories (78%, N = 56) were located within builtup areas, while most European Starling territories were located either within built-up areas (25%) or on the border of built-up areas and open areas (59%, N =41). Most Red-winged Starling nests (96%) were situated in buildings (N = 46), while European Starling nests were located both in tree holes (43%) and in buildings (57%, N = 28). Both starling species show high nest site tenacity. The Red-winged Starling daily activity pattern during the nestling phase differed considerably from that of the European Starling. Although both starling species do not overlap their feeding niches and daily and seasonal activities, their sympatric occurrence in urbanised habitats may be limited, if suitable nesting sites are lacking.

3

Nesting sites of the Great Spotted Woodpecker Dendrocopos major L. in Poland : analysis of nest cards

Hebda G.

Polish Journal of Ecology

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2009

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Vol. 57, nr 1

149-158

EN

Analysis of 531 nest cards (Polish Nest Record Scheme) of the Great Spotted Woodpecker, obtained in the years 1970-2003 is presented here. The data is derived from almost the whole of Poland, except for the Białowieża National Park. From the material processed for the purpose of this study, the Great Spotted Woodpeckers appear to nest in various types of wooded habitats, especially in forests and they are very flexible in their choice of nesting sites, both in terms of age of tree stands and intensity of human penetration. As a rule, woodpeckers breed mostly in holes made in deciduous trees (oak, birch, and alder). More than 95% of nests were excavated in tree trunks, primarily in dead or weakened trees. Woodpeckers excavated their nest in the range of 0.5-19 m above the ground, with more than 75% of them found in the narrower range from 1-7 m. The height of cavity above the ground did not depend on tree species or vegetation type and was also weakly correlated with the height of tree stands. The openings of cavities showed no statistically significant differences in their geographical orientation. Although the information about woodpecker nests, gathered in the Nest Record Scheme does contain certain errors (such as "habitat preferences" of observers), the obtained results provided a better insight into the nesting ecology of this species in Poland.