Marcin Polak

Habitat selection by breeding waterbirds at ponds with size-structured fish populations

Fish may significantly affect habitat use by birds, either as their prey or as competitors. Fish communities are often distinctly size-structured, but the consequences for waterbird assemblages remain poorly understood. We examined the effects of size structure of common carp (Cyprinus carpio) cohorts together with other biotic and abiotic pond characteristics on the distribution of breeding waterbirds in a seminatural system of monocultured ponds, where three fish age classes were separately stocked. Fish age corresponded to a distinct fish size gradient. Fish age and total biomass, macroinvertebrate and amphibian abundance, and emergent vegetation best explained the differences in bird density between ponds. Abundance of animal prey other than fish (aquatic macroinvertebrates and larval amphibians) decreased with increasing carp age in the ponds. Densities of ducks and smaller grebes were strongly negatively associated with fish age/size gradient. The largest of the grebes, the piscivorous great crested grebe (Podiceps cristatus), was the only species that preferred ponds with medium-sized fish and was positively associated with total fish biomass. Habitat selection by bitterns and most rallids was instead strongly influenced by the relative amount of emergent vegetation cover in the ponds. Our results show that fish size structure may be an important cue for breeding habitat choice and a factor affording an opportunity for niche diversification in avian communities.

Comparison of nest defence behaviour between two associate passerines

Nest predation is one of the most important factors limiting reproductive success, and antipredator behaviour can significantly reduce the loss of avian broods. I carried out field experiments on two sympatric passerines: the barred warbler and the red-backed shrike. Many authors have described the protective nature of nesting association between these species. However, we have little knowledge about the true nature of the relationships between associates. I examined (1) whether barred warblers and red-backed shrikes respond differently to an avian predator, and (2) whether males and females differ in the intensity of nest defence. Decoys of a known nest predator and a non-predatory control species were used to examine the types and relative intensity of parental response. I measured behavioural responsiveness by recording aggressive behaviour toward each model during the nestling period. Barred warblers and red-backed shrikes showed considerable variation in their response. Warblers more vigorously defended their own territories than shrikes. No differences between the sexes in antipredator behaviour in red-backed shrike were found. By contrast, in barred warbler, male was more involved in nest defence. The experimental tests provide evidence that these two species are able to differentiate between a predator and non-predator species.

Micro-habitat nest preferences of the great bittern, Botaurus stellaris, on fishponds in central-eastern Poland

The nest-site requirements of the great bittern Botaurus stellaris females in relation to habitat availability were studied in 2003–2006 at fish-pond complexes located in the Lublin and Podlasie regions (eastern Poland). The structure of emergent vegetation and water depth were measured and described in 230 control squares and 98 squares with occupied nests. Water depth, vegetation cover, the height and diameter of reed shoots, the number of flowering shoots, the density of old (dry) and new (green) reed shoots were measured. Great bittern females nested in all available types of emergent vegetation and most of the nests were located in reedbeds. Using the logistic regression model it was shown that when choosing the place for nesting the great bitterns preferred reedbeds with a high density of old-reed stems.

Temporal pattern of vocal activity of the Water Rail Rallus aquaticus and the Little Crake Porzana parva in the breeding season

Abstract. In the Water Rail the patterns of the two main types of vocalization were quite different: the announcement call was uttered throughout the breeding season with two peaks, one in April and the other in early June, but the courtship call occurred only in the pre-laying period. The vocalization period of the Little Crake is short but intensive, peaking before the start of incubation. In general, Water Rails produced more vocalizations in the evening than in the morning. The vocal activity of the Little Crake peaked at dawn. In both species a peak in vocal output occurred shortly before sunrise and before sunset.

Habitat Preferences of the Sympatric Barred Warbler (Sylvia nisoria) and the Red-Backed Shrike (Lanius collurio) Breeding in Central Poland

The phenomenon of creating a breeding association by the barred warbler (Sylvia nisoria) and the red-backed shrike (Lanius collurio) was documented relatively long ago by several researchers. Some of the authors suggest that this phenomenon is a result of similar habitat requirements rather than a product of active selection. The main goal of this study was a quantitative analysis of differences and similarities in selection of breeding habitats by both species in the area of their sympatric occurrence. Research was carried out in the years 2009–2011 in the study plot located in the Middle Vistula Valley (central Poland). The red-backed shrike preferred shrubs and open areas, however, it avoided woods and waters. The only habitat strongly preferred by the barred warbler was bushes, and this species avoided waters, woods and open areas. Neither species nested in places with a thick tree concentration. Because of differences in their feeding strategy, as opposed to barred warblers, red-backed shrikes preferred habitats with low vegetation and a low concentration of shrubs. In nest location selection, the red-backed shrike clearly preferred hawthorns, whereas the barred warbler nested also in other species of bushes. As compared with warblers, shrikes more often preferred to nest in high bushes. The knowledge of the red-backed shrikes and the barred warblers optimal habitat requirements can provide useful guidelines for future conservation projects involving these vulnerable birds.

Protective nesting association between the Barred Warbler Sylvia nisoria and the Red-backed Shrike Lanius collurio: an experiment using artificial and natural nests

The pressure of predators may significantly affects the distribution pattern of nesting birds. Some individuals may reduce the risk of predation by nesting near other species with an aggressive nest defence. In the present study I tested the predator protection hypothesis using experimental (artificial nests) and observational (real nests) approaches on two ecologically similar passerine birds–the Barred Warbler Sylvia nisoria and the Red-backed Shrike Lanius collurio. Studies have been conducted in eastern Poland in two types of habitat: river valley and farmland. The main predators of natural and artificial nests were birds, and to a lesser extent, also mammals. I found wide variation level of predation of both types of nests in different years. Nest survival rate of artificial nests was significantly lower in the farmland than in the river valley and in natural nests I observed reverse pattern. According to the predictions of the predator protection hypothesis the survival rates of the natural and artificial nests were significantly higher in territories of individuals breeding in the protective nesting association. This type of interspecific positive interaction between two associate species can be classified as facultative mutualism.

Effects of Weather Conditions, Time of Breeding, Brood Size and Hatching Order on Eurasian Bittern Nestling Growth in a Food-Rich Fishpond Habitat

The development of nestlings depends on both biological and weather factors. However, their combined effect differs among bird species. In this study, the impacts of three temperature variables, precipitation, wind speed, timing of breeding, brood size and hatching order on the growth of Eurasian bittern Botaurus stellaris chicks were analysed. Measurements of 183 nestlings from 57 nests were made at fishpond complexes in eastern Poland. Relative growth rates (RGR) were calculated on the basis of tarsus length and body mass. Generalised linear mixed models showed that brood size, hatching order and precipitation were the most important factors. Nestlings in broods of two and three grew faster than those from broods of four and five. In the largest broods, the fifth-hatched chicks had lower growth rates; this also applied to the oldest chicks in all brood-size categories. Nestlings from late-season nests showed enhanced mass and tarsus growth, while heavier precipitation and strong winds depressed growth rates. The study emphasises that even among bitterns breeding in food-rich habitats like fishponds, the chicks in largest broods run the risk of lower growth rates.

Reproduction Parameters of the Great Bittern Botaurus stellaris in the Fish Ponds of Eastern Poland

Abstract. Reproduction of the Great Bittern Botaurus stellaris was studied in fishponds in eastern Poland from 2003 to 2009. Study areas were surveyed from March to early July, and the booming period of the Great Bittern was from March to July, varying between 58 to 108 days. The start of booming activity was linked to climatic factors. We visited 143 active nests in the study population, with the majority of females starting to lay eggs at the end of April to the beginning of May. The mean clutch size was 4.8 ± 0.8 (n = 109, range 1–6). There was no significant difference in clutch size between years or within years as the season progressed. Hatching success was high 92% (n = 78 broods). For all years of the study the breeding success (measured as a proportion of successful broods to all broods) was 51% (n = 120). The mean number of fledglings (15-days old chicks) per breeding female was 1.5 (SD ± 1.7, n = 116) and the mean number of fledglings per successful female was 3.0 (SD ± 1.2, n = 58). The main mortality factor for eggs and nestlings was mammalian predation. The high breeding parameters obtained for this population were probably due to extensive fish management and the good and stable food resources in the fishponds surveyed. Long-term monitoring and study of the population structure and breeding parameters of the Great Bittern in relation to known environmental factors are an essential tool for the conservation and management plans for this threatened species.

Nest survival patterns in Eurasian Bittern: effect of nest age, time and habitat variables

Determining the key factors affecting the reproductive success of nesting birds is crucial in order to better understand the population dynamics of endangered species and to introduce effective conservation programmes for them. Inhabiting a variety of wetland habitats, aquatic birds actively select safe nesting sites so as to protect their nests against predators. The main aim of the present work was to assess the effect of temporal and habitat variables on the daily nest survival rate of Eurasian Bitterns colonizing semi–natural fishpond habitat in eastern Poland. MARK software was used for the modelling. Eurasian Bittern nests were most vulnerable to depredation at the beginning of the breeding season. This was probably because the reedbed vegetation at this time was not yet dense enough to effectively conceal the nests. There was a positive relationship between nest age and the daily survival rate. Two of the habitat variables analysed were of the greatest significance: water depth and vegetation density. In the Eurasian Bittern population studied here, nests built over deep water and in dense vegetation had the best chances of survival. The results of this work may be useful in the preparation of plans for the conservation and management of populations of this rare and endangered species. Conservation and restoration efforts that attempt to maintain high water levels will be especially beneficial to this avian species that is dependent on wetland ecosystems for breeding.

Low Prevalence but High Intensity of Infestation by Amblyceran Lice in Red-Necked Grebes (Podiceps grisegena) in Eastern Poland

Abstract. Patterns of louse infestation in waterbirds deserve attention due to potential impacts on host populations. Red-necked Grebes (Podiceps grisegena) were visually examined for the presence of amblyceran chewing lice during the 2000–2015 breeding seasons in eastern Poland. Only one species of lice (Pseudomenopon dolium) was recorded. Amblyceran prevalence was low; four young birds (2.7%) were found infested out of 147 banded individuals (66 adults and 81 chicks). However, all infested Red-necked Grebes bore heavy parasite loads. Negative consequences of infestation for physiological condition were indicated by low hemoglobin and total protein values when compared with same-age non-infested birds. The low infestation rate can be related to the biology of the host (a diving species undergoing molt at sea, solitary breeder) and the apparent high pathogenicity of P. dolium, which left numerous holes in feathers and bleeding bites in all parasitized birds.