The “costs of predation” hypothesis predicts that larger nests are more likely to be predated than smaller ones. However, nest size has not been found to be related to predation probability within any species. This study evaluated the “costs of predation” hypothesis in the Olivaceous Warbler during 2001–2003 in northwestern Bulgaria. Successful nests were significantly smaller and denser than those that were predated. Nest size decreased significantly during the course of the breeding season and increased with nest height. The relationship between nest size and the likelihood of predation was still significant even when the effects of laying date and nest height were controlled. Nest size was negatively related to fledging success even when only successful nests were considered. This finding is contrary to the prediction of the “sexual display” hypothesis, which states that nest size is positively related to fledging success, and suggests that nest size may signal phenotypic quality through the ability in this species to build a small but compact nest. It seems that both natural selection and sexual selection have led to the evolution of small nests in the Olivaceous Warbler. This is the most likely reason why the difference in nest-size between predated and non-predated nests was apparent, even in unmanipulated settings.

The influence of a parasite (larvae of Protocalliphora, Diptera: Calliphoridae) on an avian host (Blue Tit) was studied in 1994–1997 as part of a long-term research project on a population of Blue Tits inhabiting nest boxes on the island of Corsica. The Blue Tit broods were heavily infested with Protocalliphora larvae. The abundance of caterpillars as a key food type for the tits was monitored. A random sample of 16 nests was experimentally subjected to an anti-parasite heat treatment, which resulted in a marked decline in the numbers of Protocalliphora larvae. Untreated nests, with high numbers of parasites, were regarded as control nests. Under the anti-parasite treatment, Blue Tit nestlings were fed less frequently than the control nestlings (8 v. 11 food items per hour per nestling). Significant changes in the diet composition occurred, with parasite-free nestlings being consistently fed with fewer caterpillars. An average parasitised nestling was supplied by its parents with 2.6 caterpillars more than an average parasite-free chick. This suggests that in the highly parasitised control nests, the parent tits made an effort to compensate for the detrimental effects caused by Protocalliphora larvae. Feeding rate and food composition were shown to influence chick condition and survival in the nest. In spite of these facts, the nestlings in parasitised nests developed less rapidly and had lower survival rates than in the anti-parasitically heat-treated nests. The parasitic Protocalliphora larvae have a double effect on their avian host: they adversely affect nestling performance, and they compel adult tits to work harder in order to at least partially compensate for that influence.

The study was conducted from 1997–2001 in the city of Słupsk. Observations of individually marked birds were conducted from blinds located at city-centre sites where Feral Pigeons breed. The pigeons bred throughout the year, with peak broods in spring and summer. Different pairs timed their breeding such that the beginning of the season (from October to September of the next calendar year) overlapped the dates of completion (from April to December). 10% of pairs had already begun breeding in the autumn, while 86% did so between January and May. The remaining pairs (young ones, in particular) started breeding even later, mainly because of the lack of suitable nesting sites. The breeding period most often ended between August and October (75% of pairs), when the pigeons began their moult. 91% of the young birds joined the breeding population in their second calendar year of life. The remaining young birds had their first broods in the first or third calendar year of life. Pairs of young birds started nesting 2–3 months later than adult birds. The average length of a pair's breeding season was 183 days.

The Superb Lyrebird is a sexually dimorphic passerine that although is not considered endangered, it has been declining in population size since the 1940s due primarily to urban development. Recent reports suggest that lyrebirds may be threatened by chlamydial infection. We studied levels of faecal infection by two microparasites in lyrebirds: Chlamydophila psittaci and Escherichia coli in the Sherbrooke Forest, south-eastern Australia. Fresh faecal samples were obtained from 33 lyrebirds (15 adult females, 13 adult males and 5 juveniles) — estimated of 27.5% of the population, all of them tested negative to Ch. psittaci. E. coli prevalence was compared between adult males and females and no difference was found. This result is expected, for instance, if E. coli is sexually transmitted and lyrebirds are promiscuous. Trends for juveniles to be more parasitized than adults were detected, but they were statistically not significant. Behavioural analyses of video footage indicate that E. coli infected birds did not allocate more or less time to any of the activities considered than did non infected birds. This might suggest that E. coli infection in lyrebirds is relatively benign, and behavioural effects may thus be subtle. No significant differences were found in specific measurements of foraging behaviour but non infected birds tended to scratch more frequently than infected birds.

The paper analyses the effect of egg dimensions (volume, breadth, and length) on the growth and development of Tree Sparrow nestlings on successive days of life. Egg size did not influence nestling mortality. It was found that for most days of nestling life, the mean volume and breadth of eggs were positively correlated with the mean mass of nestlings in the nest. Similarly, the deviation of the volume and breadth of a particular egg from the mean egg volume and breadth in the clutch was positively correlated with the deviation of nestling mass from the mean nestling mass in the nest. Nestling growth and development in terms of asymptotic mass (g), maximum growth rate (g/day), tarsus length, and longest remex length were also positively correlated with egg size. The effect of egg size was particularly pronounced in the period of termination of intensive growth rate, development of thermoregulation, and feather development. It is possible that larger eggs contain more microelements, hormones, antioxidants, and vitamins.

The core of the limb bone cortex of mammals and birds is made of rapidly deposited, fibro-lamellar bone tissue (also present in non-avian theropods), which is usually surrounded by an avascular outer circumferential layer (OCL) of slowly deposited parallel-fibered bone. We present the first comparative allometric study of the relative OCL thickness (expressed as a fraction of the diaphyseal radius) in modern birds. Body size explains 79% of the OCL variation in thickness, which is inversely correlated with size, that is, shows negative allometry (slope -0.799). This may explain the apparent absence of OCL in the ratites. Since the OCL is deposited at the end of growth, we propose that its relative thickness probably correlates with the amount of slow, residual growth, which our results suggest to be on the average larger in small birds.

The study was carried out in the outskirts of the town of Pecs (southern Hungary) in a recultivated former coal mine. Bordered by Turkey Oak forests, this open area forms a wedge-shaped clearing in that woodland. Since trees and taller shrubs are rare in the area, it is mainly ground nesting bird species that occur in the clearing. In order to discover whether it is more advantageous to nest in the recultivated area (clearing) than in the nearby forest or at its edges, 150 artificial ground nests were constructed. On 7 May 2002, one quail egg and a plasticine egg of similar size were placed in each of the artificial nests. After a week it was found that 24% of nests in the clearing, 30% of those in the forest edge, and 44% of the ones inside the forest had suffered depredation. The proportions of damaged plasticine and quail eggs inside the forest and at the forest edge were similar, whereas the quail eggs in the clearings were significantly less damaged than plasticine eggs. Of all the experimental eggs, significantly more plasticine eggs (29%) were damaged than quail eggs (17%), which suggests that small-bodied predators are unable to break the quail eggs. 18% of the plasticine eggs attacked, and 72% of the quail eggs attacked were removed from the nest by the predator. Among the predators, small mammals were dominant in the clearing and inside the forest, and birds at the forest edge. Based on the prédation of quail eggs, the survival chances of ground nests in the clearing are greater than at the forest edge or inside the forest.

Evidence for direct interspecific competition in wildfowl and between hybrids and their parent species is scarce. This study examined threat displays and agonistic encounters (n = 324) in a goose flock of 140 Swan Geese and 13 hybrids with Greylag Goose living in Heidelberg, SW Germany. In general, agonistic behaviour made up less than 1% of the time budget throughout the year as measured by focal animal sampling. Most encounters (84%) were won by the initiator, both in Swan Geese and in hybrids. No difference was found between Swan Geese and hybrids in the outcome of an encounter, suggesting equal competitive quality. There were differences with respect to threat postures with hybrids performing diagonal neck threats more often and intentional movements less often. This seems to be related to their hybrid origin, since Greylag Geese most often show diagonal neck and forward threat displays. There was no direct evidence for hybrid superiority or inferiority.

The influence of the characteristics of habitat fragments on the dynamics of avian communities and the effect that fragments of different sizes have on the stability of the breeding species composition, and also on local extinction, colonisation and turnover rates were studied in an agricultural landscape in southern Poland. The fragments included various habitat types that differed from the matrix. Breeding birds were surveyed using the territory mapping method to assess turnover. Species composition depended on both the spatial structure of a fragment and the features of its surroundings. Local declines and appearances of species had a similar influence on the turnover in all size classes of the fragments. Species that contributed most to the total turnover were: Lanius collurio, Phasianus colchicus, Anas platyrhynchos, Emberiza schoeniclus, Columba palumbus and Sylvia communis. However, there were differences among species contributing most to the turnover according to area size classes. Heterogeneous habitats in a mosaic-like, agricultural landscape do not function as islands. The existence of species in an area with such a level of habitat patchiness can be related primarily to habitat quality, mainly because of poor isolation and the high permeability of isolating habitats.

The biology of individually colour-ringed European Blackbirds inhabiting two city parks in Szczecin (NW Poland) was studied in 1997–2003. In each park one to three observers watched the behaviour of Blackbirds every other day from dawn till afternoon (6–8 h a day); in this way almost all of their nests were discovered. 35 cases were recorded where pairs re-used their own nests, as well as two cases where the nest of another Blackbird pair and one Fieldfare nest were re-used. In 33 out of 81 cases observed, the re-use occurred after the brood had been successfully reared, while in two cases out of 378, female Blackbirds initiated the second breeding attempt in the same nest after the loss of the first one. The re-used nests were better concealed (80 ± 19% and 69 ± 18%, respectively) and had been built at greater heights than those abandoned after breeding (9.0 ± 5.0 m and 6.5 ± 4.2 m, respectively). No shortening of the interval between successive clutches was noted in the case of nest re-use (re-used nests 36.8 ± 4.9 days, newly-built nests 37.7 ± 8.0). The more and more frequent re-use of nests where breeding had been successful, their better concealment and higher sites, and also the lack of any differences in the intervals between successive clutches of pairs occupying old nests and those building new ones before the next breeding attempt, suggest that in the investigated population the basic reason for nest re-use was the insufficient number of safe nesting sites.

An abundant resident in Israel, the Graceful Warbler breeds in the northern and central parts of the country and has recently invaded desert areas following their human settlement. Possible seasonal changes in age and sex structure were investigated, as were differences in body measurements in individual sex and age classes as well as changes in the numbers of the Graceful Warbler population in Eilat. No difference was recorded between spring and autumn in the proportion of males to females, nor were significant differences found in the numbers of males and females ringed during the spring and autumn seasons. There was a significant difference in the proportion of juvenile to adult birds trapped in spring and in autumn. Moreover, males had longer wings than females in both seasons. There were no differences in body mass or body condition between sexes in the two seasons. Furthermore, adults had longer wings than first-year birds. Juveniles had longer wings in autumn than in spring, but no differences were recorded in the adults in this respect. In addition, juveniles were in better condition in spring than in autumn; however, there was no difference in body condition of the adults between seasons. The fact that a significant trend was found in the numbers of Graceful Warblers trapped in spring but no such trend in autumn, that a large proportion of recaptured birds were noted in both seasons, and that a high number of individual birds were caught repeatedly during the study period, suggests the existence of a stable or increasing breeding population in Eilat all the year round. In addition, the Bird Sanctuary is like an oasis in the desert environs of Eilat. Hence, the lack of differences among the years in the proportions of males and females between the seasons suggests that it is mainly breeding pairs that occupy the area.

This study analyzes the influence of egg laying order on egg dimensions (especially on egg volume) and on the size of the last egg laid in a Blackcap clutch. The research was carried out in deciduous woodland in NW Croatia during 2002 and 2004. The analyses covered only clutches with five eggs (the dominant size of the first clutch in the study area), where the first eggs were laid on the same day (5 May 2002 and 11 May 2004). The present study suggests that the Blackcap may employ a strategy of increasing the egg volume of each successive egg laid, which may reduce size hierarchy between nestlings and prevent competition between them.