The probability of successful breeding by Brent geese in the Arctic appears to be positively correlated with the mass of females when they depart from spring staging areas in North-western Europe. To clarify the mechanism behind this relationship we investigated the significance of flown-in female body stores for breeding over six summer seasons (1990–1995) in the Pyasina Delta in Taimyr, Russia. Female Brent Geese were caught upon arrival on the breeding grounds. Changes in female body mass and the timing and duration of nest recesses were recorded via electronic weighing platforms placed under their nests. Average female body masses declined through the breeding season; from 1464 g at arrival to 1269 g after egg laying and 1066 g at hatching, which was supposed to be close to lean body mass. Thus half of the stores were used between arrival and clutch completion, the other half during incubation. All females foraged during incubation. On average they left the nest 13.1 times every 24 hours, resulting in a daily recess time of 198 min during the first 21 days of incubation. Females were less likely to leave the nest during the last three days of incubation. Leaving the nest was risky: 40% of the Brent Goose nests in the study area lost one or more eggs to gulls during absence of the female. We estimated that 52% of the energy required during incubation was derived from body stores and the rest (48%) from food intake.

We focused upon habitat use and home range size variation in an alpine population of the Black Woodpecker Dryocopus martius. Habitat selection analyses showed that the dominant local forest type, i.e. Mountain Pine Pinus mugo uncinata, was significantly avoided. Scots Pine Pinus sylvestris stands were positively selected, likely because of the abundance of ants; Beech Fagus sylvatica was chosen for nesting and roosting. A high level of flexibility in ranging behaviour and habitat selection, with remarkable among- and within-individual variability, was recorded. We assessed the reliability of census techniques by comparing results obtained by radio-telemetry and territory mapping, which showed that territory mapping failed to identify all pairs detected through radio-tracking. Several behavioural and ecological traits may bias count results irrespective of the methods used. Mapping methods are particularly ineffective because the Black Woodpecker is weakly territorial: in our study area home range overlap was rather high and no territorial defence was detected. Based on these results, the potential of the Black Woodpecker as ecological indicator is questioned.

This study analyses the effects of nest-site selection on predation risk of Great Bittern Botaurus stellaris nests. The study was conducted in fishponds of eastern Poland during four breeding seasons (2003–06). The habitat characteristics of 84 nest sites were investigated. Nesting sites were found within Phragmites, typha, Carex and Scirpus vegetation in the reed belt surrounding the fishponds. All nests were built at places having between 10 and 97 cm of water depth. Predation was the major cause of nest failure in the study population. However, no relationship between nest site vegetation type and daily nest survival rate was found. The survival of nests at edges and in the interior of reed beds was similar. A logistic regression model indicated significant effects of water depth and vegetation cover on nest predation in the Bittern population. There was a tendency towards better success for nests in dense emergent vegetation with higher water depth. The results have important implications for an effective conservation strategy for wetlands holding large and viable populations of this vulnerable species.

Effects of agricultural intensification on availability of grassland invertebrates as food for chicks of the declining Black-tailed Godwit Limosa limosa were studied in The Netherlands. Invertebrates were sampled with photo-eclectors in wet grasslands used for intensive dairy farming (high fertiliser input, 2–3 cuts starting early to mid-May) and in a meadowbird reserve (moderate fertiliser input, one cut in mid-June). Invertebrates were slightly more abundant in reserve than in agricultural fields before the first cut of the latter. In the 4–6 weeks between the first cut of agricultural fields and that of reserve fields, invertebrates were much more abundant on reserve fields. This is the main period of godwit chicks' presence. Mean size of arthropods was similar under the two management regimes, but large Coleoptera were more abundant in agricultural fields early in the season. In a foraging experiment, captiveraised godwit chicks ingested 31% fewer prey per unit time when foraging in cut agricultural grasslands than in uncut reserve fields, a difference large enough to compromise chick growth and survival. Wild broods strongly selected to stay in reserve fields, especially after agricultural fields had been cut, and travelled towards reserve fields over distances up to more than 0.5 km. Preference for reserve grasslands declined from early June onwards. We conclude that postponing mowing dates, in reserves or on farmland by means of agri-environment initiatives, improves feeding and survival conditions for godwit chicks and other insectivores feeding in the grassland sward, in addition to its beneficial effect on hatching success.

Hatching success has been considered one of the main factors associated with fitness in birds. Hatching failure could be the result of two independent events, infertility and death of embryos, which have not been independently considered in most studies. Our study analyses hatching failure pattern in a precocial bird, the Red-legged Partridge Alectoris rufa. In trials with captive birds, we tested effects of egg size, laying order and clutch size on infertility and embryo death controlling for maternal condition and age. On the basis of previous studies we predicted that lighter eggs show higher rates of infertility and/or embryo mortality. We also predicted that infertility prevails in first and last-laid eggs.

Infertility represented the most important component of hatching failure in Red-legged Partridge. The importance of egg size in determining hatching success was supported because infertile eggs were lighter than fertile ones. Infertility prevailed in first seven eggs of the sequence of laying supporting previous findings. Hatched and unhatched fertile eggs showed similar weights, but embryo mortality increased with the sequence of laying. Clutch size and maternal body condition did not account for differences in infertility or embryo mortality. We suggest that infertility and embryo death might be caused by physiological constraints on both parents.

Late-hatched Great Tits Parus major have often a lower local recruitment rate than those hatched early. However, estimates of recruitment usually neglect differential disappearance due to dispersal. We report on the proportions of late-hatched breeders in two Great Tit breeding populations (near St. Petersburg, NW Russia, and on the Courish Spit, Eastern Baltic). Using a novel method, late-hatched birds (hatching in July) were distinguished in the next breeding season by the incomplete moult of their tail feathers. Based on this method, we were able to estimate the percentage of late-hatched individuals in all first-year birds, including immigrants. The proportion of late hatched breeders was considerable in some years, and appeared related to the proportion of late fledglings in the previous year. In the Courish Spit population we found no significant difference in the global recruitment rate (accounting for both local birds and immigrants) of early- and late-hatched Great Tits. In the St. Petersburg population, the annual percentage of late-fledged breeders was significantly lower than the percentage of late-hatched fledglings in the previous year. However, in the St. Petersburg population we cannot definitely conclude that the global recruitment rate of late fledglings was lower than that of early fledglings because of peculiarities of the study site. We also can suggest that it may be a result of competition between early and late fledglings, winter residents and newcomers in spring (especially in males), as well as a result of different survival of early- and late-born individuals during the first year.

On Bonaire we assessed Bam Owl Tyto alba diets at four discrete sites. The 233 fresh pellets contained 755 identifiable prey items from four taxonomic orders. Average prey diversity differed two- to threefold between sites. Dietary composition showed large spatial variations between sites, from predominantly insectivorous to avian. Between-island variation was assessed by comparing the dietary composition of populations of Barn Owls on nine islands throughout the Caribbean region as reported in the literature. On 8/9 islands mammals (mainly rodents and bats) formed the main diet. On half of the islands about a fifth or more of the prey comprised birds. Reptiles and/or insects were eaten on 5/9 islands, but rarely dominated the diet. These large within-island dietary differences reflect differential prey availabilities in the Caribbean, possibly enhanced locally by specialisation.

Raptor migration has been monitored regularly at Gibraltar since the mid-1960s. Long-term trends in abundance of spring migration were investigated for the ten most frequent species, five of which changed significantly in abundance during the study period. Black Kites Milvus migrans, Eurasian Sparrowhawks Accipiter nisus and Booted Eagles Hieraaetus pennatus increased. The trends for these three species correspond with those observed elsewhere in western Europe. European Honey-buzzards Perms apivorus and Common Buzzards Buteo buteo, whose western European populations are described as stable, both decreased. For Common Buzzards at least this discrepancy appears to represent a shift in wintering distribution, possibly as a result of climate change, with populations that wintered formerly in North Africa now wintering closer to their breeding grounds.

Spring migration of Willow Warbler Phylloscopus trochilus over the western Mediterranean was studied using observations collected at a ringing station on the mainland of Spain (Aiguamolls de l'Empordà), and at an island station (Cabrera, one of the Balearics). During the years 1993–2001, birds were caught and measured between 16 April and 15 May. The peak of captures and mean arrival date was seven days earlier on the continental station than on the island. At both stations long-winged individuals passed before short-winged birds, and birds at the continental station had longer wings than at the island. The number of recaptures was low at both locations suggesting that most birds departed at the day of arrival. The mean stopover period for recaptured individuals at the continental and island station was 2.2 and 2.6 days, respectively. Body mass remained more or less constant during this stay. Our observations suggest that subpopulations of Willow Warblers, differing both in morphology and timing of migration, have different migration routes over the western Mediterranean; one migrates over the Iberian Peninsula and another crosses over the sea.

For Red Knots Calidris c. canutus sandy coasts of the southern Baltic seem to be a low quality stopover site, because of unpredictable feeding conditions and a low density of molluscs. Observation collected in the Puck Bay, Poland, suggest that Knots feed mainly on Nereis sp., Gammarus sp., small sized Hydrobia sp. and small insects taken from wet sand. Among 1471 Knots ringed 27.8% of juveniles and 10.5% of adults were retrapped few days after the first capture, which indicates that the majority had a short stay and apparently departed with small energetic reserves. In spite of poor feeding conditions the fuel deposition rate of the Knots in autumn (adults: 2.4 g per d, juveniles: 2.7 g per d) was similar to that observed in the Dutch Wadden Sea and the Baltic coast of SE Sweden. It is suggested that Knots are able to accumulate body stores despite low food quality and density because the lack of tides allow them to forage without interruption, and because there is no additional energetic cost related to increasing gizzard size.

Standard reviews list Arctic Warbler Phylloscopus borealis as a probable breeder in northern Korea, as well as passage migrant; the most recent states that spring passage begins c. 10 April and finishes within May. Near-daily structured counts in north-central Korea (Pyongyang and Hyangsan) during 2000–2003 showed, by contrast, that regular spring passage runs from early-mid May into early June, and that autumn return begins in early August, dates reflecting modern data from elsewhere in East Asia. Specific searches in the Myohyang Mountains, site of most postulated ‘breeding’ records, found no evidence of summer residency, let alone breeding. Korean breeding was assumed from records outside the then-perceived passage seasons, but these perceptions were flawed and, combined with misidentification, led to the unsupportable conclusions of breeding. In fact, a summer gap in acceptable past records spans almost the same dates as today's summer absence from Pyongyang and Hyangsan, both undoubtedly only passage sites. The species may yet be found to breed in northern Korea, but there is no evidence, even circumstantial, that it does so. Past assessments that regular passage begins in mid April were evidently in error, reflecting past difficulties of species identification.

Sexual segregation during foraging is common in birds and may occur at different temporal and spatial scales. In this study we explored the degree of sexual segregation in the Black Skimmer Rynchops niger by studying the species and sizes of prey consumed by either sex. Moreover we assessed the distribution of the sexes over the study area. We developed a multivariate tool for sex determination in Black Skimmers by using morphometric measurements from birds of known sex. Birds captured with mist nets and museum skins were analysed. The sex of birds was determined by PCR amplification of DNA or by gonad inspection. The fish prey remains obtained from spontaneous regurgitations of captured birds were used to estimate total length and weight of consumed fish prey. The bulk of the diet of both sexes was generally composed of the same species (mostly silversides Odontesthes spp.), but males consumed larger prey than females. The sex ratio in the lagoon was strongly skewed towards females. We discuss the implications of sexual segregation for habitat and species conservation measures.

Jack Snipe Lymnocryptes minimus is a small wader showing sexual monomorphism in plumage and some dimorphism in size. To study whether parameters of body size may be used to reliably sex individuals of this species, a discriminant function analysis was applied to a set of morphometric traits measured in birds caught during migration and the wintering period in northern Poland. Birds were sexed molecularly based on size differences in CHD-linked sequences from W- and Z-chromosomes. Males were significantly larger than females in wing length, head length, skull length, bill depth, bill width and the length of middle toe with claw, while females had longer bills. All traits except for bill width were highly repeatable. A stepwise discriminant function analysis selected wing length, skull length, bill length and bill depth as the best discriminators of sex in Jack Snipe. The discriminant function based on these four traits enabled reliable sexing of 99% of individuals. The alternative function, excluding wing length, which may not always be available for measurement, showed 96.7% classification success. Such very high success in sex identification by a discriminant analysis of morphometric traits may promote this approach as an alternative to molecular sexing techniques in Jack Snipe, when non-invasive sampling is required.

Although lead poisoning is common in swans, no information exists on the prevalence of lead artifact ingestion in swans using the lower Great lakes (LGL). We examined artifact ingestion (lead and non-toxic) in Mute Swans Cygnus olor and Tundra Swans Cygnus columbianus collected on the LGL in Ontario (1999–2003) following the 1999 ban on use of lead shot for waterfowl hunting in Canada. A larger proportion of Mute Swans (19.8% of 243 birds) contained artifacts than did Tundra Swans (6.5% of 77 birds), possibly due to the fact that Mute Swans feed exclusively in aquatic habitats. Overall, 14% of Mute Swans contained nontoxic shot, 6% contained lead shot and 1.6% contained fishing tackle; 4% of Tundra Swans contained non-toxic shot and 2.6% contained lead shot. Adult Mute Swans (22.7%) had a higher incidence of artifact ingestion than did cygnets (8.9%), but there were no age-related differences in Tundra Swans. No sex-related differences in artifact ingestion were detected in either species. Given the overall frequency of shot ingestion in Mute Swans (20% of birds), lead toxicosis probably was a significant mortality factor for this species on the LGL before the lead shot ban. As only 1.6% of Mute Swans and no Tundra Swans contained any form of fishing tackle, angling related injuries and mortalities are likely lower in the LGL than has been reported for swans in Europe. Presently, lead toxicosis is likely having a low to moderate effect on Mute Swans and a minimal effect on Tundra Swans on the LGL.

Mating patterns in hybrid zones may be important for maintaining a stable hybrid zone. Theory suggests that hybrid zones are stable due to assortative mating outside the zone. To test whether assortative mating occurs in the crow hybrid zone in eastern Germany, I studied pairs of crows. The study area between Magdeburg and Dresden was divided into a grid and in each grid cell I recorded paired crows between 8 April and 12 July 2006. Carrion Corvus corone and Hooded Crows C. cornix mated assortatively given that the composition of observed pairs deviated significantly from what was expected by random mating; homotypic pairings, i.e. Carrion × Carrion or Hooded × Hooded Crows, were observed more and heterotypic pairings less often than expected. These findings contradict previous suggestions for this region but are in accordance with studies in other parts of Europe.

Ragworms Hediste diversicolor are an important prey item in the diet of many estuary birds. The standard method for estimating the number of Ragworms in faeces or pellets is simply dividing the counted number of Ragworm mandibles by two, which can easily lead to an underestimation of the real number of Ragworms present. Here, I present two alternative methods, which avoids bias in estimates of the number of Ragworms in samples. I compared the three methods by applying them to faecal samples of Grey Plover Pluvialis squatarola and Redshank Tringa totanus from the Tagus estuary, Portugal. The alternative methods yielded significantly higher estimates of the number of Ragworms present in each sample, a difference that can have repercussions on the outcome of dietary studies of Ragworm predators. The pros and cons of each method are discussed with regard to the use of faeces and pellets for ecological research, and the situation in which each method could be applied is discussed.