Interspecific variation in the relationship between clutch size, laying date and intensity of urbanization in four species of hole-nesting birds

The increase in size of human populations in urban and agricultural areas has resulted in considerable habitat conversion globally. Such anthropogenic areas have specific environmental characteristics, which influence the physiology, life history, and population dynamics of plants and animals. For example, the date of bud burst is advanced in urban compared to nearby natural areas. In some birds, breeding success is determined by synchrony between timing of breeding and peak food abundance. Pertinently, caterpillars are an important food source for the nestlings of many bird species, and their abundance is influenced by environmental factors such as temperature and date of bud burst. Higher temperatures and advanced date of bud burst in urban areas could advance peak caterpillar abundance and thus affect breeding phenology of birds. In order to test whether laying date advance and clutch sizes decrease with the intensity of urbanization, we analyzed the timing of breeding and clutch size in relation to intensity of urbanization as a measure of human impact in 199 nest box plots across Europe, North Africa, and the Middle East (i.e., the Western Palearctic) for four species of hole-nesters: blue tits (Cyanistes caeruleus), great tits (Parus major), collared flycatchers (Ficedula albicollis), and pied flycatchers (Ficedula hypoleuca). Meanwhile, we estimated the intensity of urbanization as the density of buildings surrounding study plots measured on orthophotographs. For the four study species, the intensity of urbanization was not correlated with laying date. Clutch size in blue and great tits does not seem affected by the intensity of urbanization, while in collared and pied flycatchers it decreased with increasing intensity of urbanization. This is the first large-scale study showing a species-specific major correlation between intensity of urbanization and the ecology of breeding. The underlying mechanisms for the relationships between life history and urbanization remain to be determined. We propose that effects of food abundance or quality, temperature, noise, pollution, or disturbance by humans may on their own or in combination affect laying date and/or clutch size

Variation in clutch size in relation to nest size in birds

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Marginal differences between random plots and plots used by foraging White-backed Woodpeckers demonstrates supreme primeval quality of the Bialowieza National Park, Poland

I compared structural characteristics between foraging plots of an endangered European species, the White-backed Woodpecker Dendrocopos leucotos (WbW), and random plots in primeval deciduous stands of Białowieża National Park. I expected that WbW would use plots with higher amount of dead wood in more advanced decay stage, with higher amount of birches Betula spp. and aspen Populus tremula, and with more large trees. Within 50, 0.25-ha plots (25 used by WbW and 25 random) tree-species composition, tree condition, tree diameter at breast height DBH and characteristics of dead trees were measured. WbW and random plots were similar in overall structure; only the volume of fallen timber was significantly larger in WbW than in random plots (65.3 and 47.4 m3/ha, respectively). There was also a tendency for the occurrence of more snags of 11 -20 cm DBH within WbW plots. Thus, the amount of fallen timber might determine WbW choice of the foraging habitat. However, due to the relatively high similarity of WbW vs. random plots, the sections of Białowieża National Park that are covered with old-growth deciduous stands represent high-quality habitat for WbW foraging

Ecology and biology of birds in the Bialowieza Forest: a 40-year perspective

The aim of this study was to review the most important results from the last 40 years of intense ornithological research conducted in the Białowieża Forest. Furthermore, we discuss the threats that may destroy the unique ecology and characteristics of this forest. Studying the avifauna of the Białowieża Forest provides us with a good general knowledge about natural ecological conditions and relationships, which prevailed in temperate European forests in the past. The avifauna of the Białowieża Forest is characterized by features associated with primeval habitats such as the stability of communities over time, high species richness, relatively low densities, high proportion of hole-nesting birds, very high predation pressure and weak, insignificant competition interactions. This emphasizes the importance of predation, excess of nesting sites for cavity nesting birds, high abundance of food, especially for insectivorous species and fluctuation of bird population size due to rodent outbreaks (pulsed resources). The most severe threats for the avifauna of the Białowieża Forest are: rejuvenation of tree stands, removal of dead wood, fragmentation of old-growth stands, change of tree stand composition (reducing the proportion of some tree species). In order to expand our ecological knowledge about birds, we should keep the Białowieża Forest fully protected for years to come. The main priority should be the maintenance of natural processes changing the forest’s species composition

Natural nest sites of the Collared Flycatcher Ficedula albicollis in lime-hornbeam-oak stands of a primeval forest

Knowledge of habitat and nest site selection of secondary hole nesting birds under primeval conditions may aid in managing forests and in conservation biology. We studied location (n = 768) and dimensions (n = 624) of Collared Flycatcher nests in natural tree holes in a lime-hornbeam-oak stand of the Białowieża National Park, Poland. Collared Flycatchers bred most often in hombeam Carpinus betulus, in holes that were on average 8.1 m above the ground in trees of a mean diameter at breast height (DBH) of 43 cm. The majority of nest holes were situated in tree trunks (79%), with most of these (87.9%) in living trees. Nest holes were either originally made by woodpeckers (17.4%), or created by natural decaying processes. The minimum diameter measurement of the entrance hole for all Collared Flycatcher nests was 4.6 cm on average. The average distance between the outer rim of the entrance hole and the floor of the nest cavity (danger distance) was 25 cm. The median floor area of the nest cavity was 96 cm2. Differences between orientations of the hole entrances were insignificant

Nest soaking in natural holes-a serious cause of breeding failure?

Nest loss rates of four secondary hole-nesters - Pied (Ficedula hypoleuca) and Collared (Ficedula albicollis) Flycatchers, Marsh Tit (Parus palustris) and European Nuthatch (Sitta europaea) - due to soaking recorded during a long-term study in a primaeval temperate forest (Bialowiez̀a National Park, Poland) were low. Even during extremely heavy rains (> 74 mm in one day) they did not exceed 11%, far less than the loss due to predation. Soaking of nests occurred significantly less often in the late (flycatchers) than in the early breeding species (Nuthatches and Marsh Tits). In the latter species partial brood losses due to nest soaking were observed as well, the partial nest loss being more frequent in the rainy seasons. Interior walls of 8-40% holes were moist due to sap drain, but this only exceptionally led to the total nest failure. We suggest that the main function of bulky nest foundations in all these species may be protection against moisture

Availability of tree cavities in a sal forest of Nepal

Tree cavities are important structural elements of forest ecosystem that host numerous birds, mammals and other cavity-dependent organisms. Pattern of cavity distribution in temperate and boreal forests are relatively well studied, yet little is known about cavities in tropical and subtropical forests. We compared cavity availability in relation to tree condition (living tree and snag), tree species and DBH class between two different sites in a subtropical deciduous sal forest in Nepal: the Chitwan National Park Forest (the park site) and the Khorsor Buffer Zone Forest (the buffer site). Surveys for tree cavities were conducted in 2013 on 50 circular sample plots of size 0.1 ha. We recorded 40 cavity trees in the park site and 31 cavity trees in the buffer site. Density of cavities was on average 22.4 ha-1 in the park site and 19.2 ha-1 in the buffer site. Cavities occurred mostly in living trees (85.9% cavity trees) and were formed mostly by damage and decay (natural cavities: 74%) or by woodpecker activity (excavated cavities: 26%). Most were observed on three tree species: Shorea robusta, Dillenia pentagyna and Syzygium operculatum, with a mean diameter of 43 cm (range: 12-111 cm). S. operculatum, Myrsine semiserrata and Semecarpus anacardium were overrepresented among tree species with cavities. In snags, 25.0% of all cavities were found in the park site and 8.3% in the buffer site, while snags represented 4.2% and 2.2% of all trees in the two sites, respectively. Statistical anaysis indicated that tree species, tree condition and particularly diameter (DBH) were important variables for the prediction of cavity presence. We recommend cavity-bearing tree species to be better protected by forest management in order to help maintain the community of cavity dwellers