The study was carried out in 1999–2000 in a 405 ha area urban habitat and revealed one of the highest densities (56.8 pairs/km²) for the species. Breeding density was best predicted by the diversity of trees in the plot and was not limited by the presence of tall trees. Birds used 69% of the available tree species and preferentially selected half of them. Taller tree species were preferred to shorter ones and coniferous trees were preferred to broadleaved ones. Nests higher above the ground were more likely to be successful than nests lower down. The greater the nest height, the earlier the Magpies laid eggs and the more fledglings they produced. Pairs nesting in conifers laid earlier than those in broadleaved trees but there were no significant differences in clutch-size, hatching or fledging success between the two habitats. The nest site preference was not well explained by the success rate. Regardless of species, not only tall trees, where success was greater, were preferred but also smaller ones, despite the lower success rate. Nests in conifers were no more successful than those in broadleaved trees, despite the marked preference for conifers. Magpies that succeeded in their final breeding attempts in one season were less likely to make a contrasting nest-site choice the following season. The lack of a clear adjustment between the nest-site selection pattern and breeding success was hypothesized to be due to two non-exclusive mechanisms: 1) either there are no strong selective pressures at any type of nest-site and on the behavioral plasticity of Magpies or else selective pressures may change during the season; 2) the dependence of nest-site selection on bird quality.

Foraging observations (1 observation/bird) of tits and associated species were recorded during four winter months in two natural old-growth and two managed forests. The number of daily foraging observations was used as an index of bird abundance. The daily mean number of foraging observations for Parus major, P. caeruleus, P. palustris, Sitta europea, Certhia familiaris and Dendrocopos major was significantly higher in natural old-growth vs managed forest (ratio 4.8 : 1 for all six species pooled and 3.1 : 1, 3.2 : 1, 4.7 : 1, 5.7 : 1, 7.4 : 1 and 4.7 : 1 for the above-mentioned species, respectively). As the larger dominant species has an advantage in competition for nest holes, we would expect these to exhibit the smallest abundance ratio skews. This was not, however, the case and consequently, the results of this study do not support the hypothesis that a lack of nest holes should be the primary limiting factor for hole nesting species in managed forests. It was found that the species showing the strongest preference for foraging on dead wood were the same that had the most pronounced density skew between forest types. This could indicate that the lack of food resulting from silvicultural practice could be very important as a limiting factor in managed forests. Analyses of the use of dead wood of different diameter and from different tree species indicate that forest birds exploit diverse types of dead wood. Partially decayed standing dead wood was the most important substrate for the majority of species.

The distribution of breeding House Martins was examined in relation to the characteristics of the urban landscape and the structure of the buildings. The study area (73 km²) was divided into 700 × 700 m squares. 11 habitat characteristics were measured within a 300 m radius around each colony. Each nest site was classified according to nest-support-type, its height and orientation. Habitat features around colonies were compared with places at the center of those squares without colonies. Stepwise multiple regression was then used to assess the possible contribution of the independent variables to the size of the colonies. A total of 1399 nests were found, distributed in 120 colonies, mostly consisting of 1–5 nests. In the built-up area, the density reached 31.85 nests per km². House Martins selected areas with a larger proportion of old buildings and open spaces, and closer to the nearest sources of food or mud. Only the distance from colonies to the nearest mud source and the proportion of open spaces were included in the regression model. As far as nest-sites are concerned, 33% of all nests were built under eaves, 34% under the ledges of balconies with architectonic ornamentation, and 15% within balconies. Birds selected nest sites offering better adhesion of nests to the substrate; to compensate for poorer adhesion, the number of nest walls touching other nests was increased. There was a positive relation between nest site height and building height. Nests were not uniformly distributed around the circle, but no clear patterns emerged from the data.

Migratory Red-backed Shrikes were mist-netted during the spring and autumn migrations (n = 1031 individuals) from 1984 to 2001 in Eilat (Israel). In a similar pattern of trapping, more than four times as many shrikes were caught during autumn than in spring. Males migrated significantly earlier than females in spring but not during the autumn migration, which suggests that in males there is a stronger drive to reach their breeding territories early. In both seasons and between both sexes we did not find any significant relations between the body measurements of individuals and the time of passage. The spring migration was much shorter time than the autumn migration. This was expressed by the minimum stopover duration, as well as by the time when Red-backed Shrike occurred in Eilat. There are significant differences between wing chord length, body mass and fat scores between seasons. In autumn males had longer wings, and both sexes were heavier and in better condition than in spring. The data suggest that the differences are an adaptation to their having to cross the Sahara Desert. The birds spend a statistically significantly shorter period of time at the Eilat stopover site in spring than in autumn (median 1 ± 1.5 days vs 5 ± 6.5 days). In autumn, recaptured birds were 6.3% heavier than during the first capture. The change in body mass was significantly correlated to the duration of the stopover period. The results suggest that migration over desert is energetically costly and that Eilat is a very important stopover site for migrating Red-backed Shrikes.

This study is based on an analysis of nest-histories of 652 Collared Flycatcher nests found in natural tree cavities in the Białowieża National Park in 1988–1999. The secondary-cavity-nester Collared Flycatcher constitutes migratory single-brooded population breeding in high density in the primeval oak-lime-hornbeam (Querco/TillioCarpinetum) stands. Nest predation was the main reason of the breeding losses (240 nests) accounting for 91% (82%–100%) of them. Local production of fledglings was affected by nest predation caused by rodents, mustelids and Great Spotted Woodpecker. In this study a link between forest rodent cycles and the Collared Flycatcher fluctuations in number was documented. Number of produced fledglings depended on both, positively the number of the Collared Flycatcher breeding pairs in year N and negatively on the Yellow-necked Mouse density in year N. Rate of nest destruction is related to the density of the Yellow-necked Mouse recorded in BNP, while independent on the Collared Flycatcher density (nest predation limiting but not regulating). The predation pressure in some years keeps the Collared Flycatcher density at a level well below that of the potential the habitat resources (nest-sites, food). Local breeding density was shaped by fledglings productivity (breeding success) of the previous year. Earlier hypotheses concerning the Collared Flycatcher and other birds population limitation were also discussed.

This paper reports on the case of selection, due to influence of bad weather on nestling number, acting through different pathways on breeding date and morphological traits in breeding Great Tits. Multiple regression of relative fitness on tarsus length, bill height and forearm length, revealed significant phenotypic selection on male forearm length and female bill height. However, nestling mortality during the bad weather depended on their age, which suggested breeding date as a focal trait for selection. The multiple regression analysis of relative fitness on both body traits and hatching date shows that in males only breeding date was significantly related to fitness, and selection on forearm resulted from correlation of forearm with hatching date. A similar analysis in females shows that both bill height and timing of hatching were equally related to fitness, therefore in this sex both bill height and date of hatching were focal traits for selection.

Brood size in birds is reduced through fatal starvation, siblicide or parental infanticide (killing of own offspring). Both Black and White Storks were observed practising facultative parental infanticide. In the White Stork parents regurgitate large amount of food consisting of many small items on the nest bottom. Chicks pick up food themselves, trying to eat as quickly as possible. No aggression among chicks is observed. As a result monopolisation of food does not occur and elimination of the weakest chick is very ineffective. Sometimes parent storks accelerate brood reduction by killing some of the offspring. Surprisingly, although parental infanticide is a quick and efficient method of brood reduction it is rarely observed, even in species practising it.

The study relates to the Little Owl Athene noctua, Barn Owl Tyto alba, Tawny Owl Strix aluco, and Longeared Owl Asio otus. By coexistence is meant the simultaneous nesting, or territorial occupation in the breeding period, of more than one owl species within the area of one farm. Altogether, 48 territories of owls in 16 farm building complexes were found. Distances between nearest-neighbour nest sites were 16-203 m. In the Little Owl the average distance was 43 m ± 28, in the Tawny Owl 159 m ± 61. The number of young in broods of Little Owls nesting in coexistence was significantly lower compared to those nesting with other owls. The considerable incidence of coexistence found was related to the specific conditions of the study area: “islands” of farm building complexes offered favourable nesting sites, while the surrounding monoculture fields provided hunting territories with only limited opportunities for nesting. The productivity of the Little Owl and Barn Owl in the study area was low, probably because of interactions brought about by nesting in close proximity.