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Cooperative breeding is rare in shorebirds, and when found it is thought to be due to polygamous mating (cooperative polygamy). Here we describe the social structure of cooperatively breeding groups in Southern Lapwing Vanellus chilensis and test the prediction that offspring sex ratio is skewed towards the sex that helps. The social groups consisted of a breeding pair with one or two young (mostly males, 68%) from the previous breeding season, and offspring sex ratio was not skewed. Cooperative breeding in the Southern Lapwing is not the consequence of cooperative polygamy, but rather groups were formed by a mated pair and some of their offspring from previous nests as helpers.

An influential period in avian life-cycles is the annual breeding season, when competition over suitable nesting-sites and territories is a key factor that can determine fitness and distribution, especially for highly species that are highly selective in their nesting habitats. We analyzed nest-site characteristics, breeding success and competitive interactions between two apex predator populations. Whereas the Short-toed Eagle has nested in the Judean Foothills (Israel) for a long time, the Long-legged Buzzard has only invaded the nesting habitat of the Short-toed Eagle during their breeding season in the last two decades. These two recently sympatric species have similar nesting ecology and frequently use the same nests. They are therefore expected to compete over nesting sites and territories. We analyzed interspecific interactions between these two species by combining information from comprehensive observational, experimental, GIS analysis and remote sensing data, deriving 65 variables to characterize the nest sites used and breeding success in 381 breeding attempts over four consecutive breeding seasons. To assess interspecific and intraspecific territorial behaviour and aggressiveness, stuffed Long-legged Buzzards and Short-toed Eagles were presented close to nests. Nest-site characteristics overlapped substantially between species, and Long-legged Buzzards occupied 21% of all Short-toed Eagle nests. Intraspecific aggression rates among Long-legged Buzzards were higher than their interspecific aggression rates with Short-toed Eagles and also higher than intraspecific aggression among Short-toed Eagles. Long-legged Buzzard and Short-toed Eagle breeding densities (1.59 ±0.11 and 2.96 ±0.11 pairs per 10 km2, respectively) are likely to be the highest across their respective breeding distributions, with a maximum productivity of 0.96 ±0.01 and 0.56 ±0.05 (young fledged/breeding pair) for Long-legged Buzzard and Short-toed Eagle, respectively. Intraspecific interactions among both species play an important role in determining their breeding success and the spatial distribution of nesting-sites. Our results suggest that interspecific competition over nesting-sites and territories between both species, and the potential dominance of Long-legged Buzzard, has both direct and indirect impacts on the spatial and demographic distribution of Short-toed Eagles due to the recent establishment of Long-legged Buzzard territories in the Judean breeding area. This article is protected by copyright. All rights reserved.

Seabird numbers can change rapidly as a result of environmental processes, both naturaland anthropogenic. Informed management and conservation of seabirds requires accurateand precise monitoring of population size. However, for burrow-nesting species this israrely achieved due to spatial and temporal heterogeneity in burrow occupancy. Here,we describe a novel method for deriving more accurate population size estimates thatemploys mark-recapture methods to correct for unknown variation in nest occupancythroughout a breeding season. We apply it to estimate breeding numbers of a colonial,burrowing seabird, the Little Penguin Eudyptula minor, on the Summerland Peninsula,Phillip Island, Australia. Estimates of active burrow numbers during the September 2008to February 2009 breeding season were adjusted to numbers of breeding birds based onburrow occupation and modelled population demographics at six, fortnightly monitoredreference sites. The population was estimated to be 26 100 (95% CI: 21 100–31 100)and 28 400 (23 800–33 000) breeding Penguins in two temporally separated surveyswithin one breeding season. We demonstrate using simulation that the method is robustto variation in burrow occupancy throughout the breeding season, providing consistentand more accurate estimates of population size. The advantage of using the correctedmethod is that confidence intervals will include the true population size. Confidence lim-its widened as burrow occupancy declined, reflecting the increased uncertainty as largeradjustments for low burrow occupancy were required. In contrast, the uncorrectedmethod that uses burrow occupancy alone as a measure of breeding numbers wasinconsistent and significantly underestimated population size across much of the breedingseason. Although requiring considerably more survey effort, the corrected approachprovides a more accurate means for monitoring population changes in colonially breedinganimals while collecting demographic data that can help diagnose the drivers ofpopulation change.Keywords: Australia, Eudyptula minor, Little Penguin, mark-recapture, nest-site occupancy.Population size is a key statistic to monitor howecological processes influence wild populations butaccurate estimates of population size are difficult toachieve for many animals. Many animals, includingseabirds, build nests, which provide a temporallyand spatially stable index of their abundance(Rayner et al. 2007). The most common techniqueto estimate the number of breeding seabirds in largepopulations has been to predict an appropriate timeto survey active nests, assume that each active nestrepresents a breeding pair, estimate density from arepresentative sample of the population, and applythat density to measured areas of occupancy(Lawton et al. 2006, Priddel et al. 2006, Rayneret al. 2007, Reyes-Arriagada et al. 2007, Barbraudet al. 2009, Bragg et al. 2009, Charleton et al.2009, McKechnie et al. 2009, Newman et al. 2009,Scott et al. 2009). While allowing a general popula-tion size to be interpreted, this technique makesnumerous assumptions that are in many casesuntested and may have a large and variable influ-ence on estimates between years. Hence, only largechanges in population size can be detected reliably.

The ideal free distribution (IFD) model predicts that a density-dependent mechanism operates to regulate habitat selection and reproductive performance. We studied a Little Grebe Tachybaptus ruficollis population, which breeds on irrigation ponds in the Vega Baja Valley (southeastern Spain) to test the premises of the IFD model. These ponds are highly dynamic because they are managed according to agricultural requirements, and are subject to different levels of disturbance, which can change the quality of individual ponds across the landscape. Surveys were carried out during the breeding season from 2002 to 2006, with reproduction performance estimated during two consecutive breeding seasons, 2003 and 2004. Occupation frequency differed from random, indicating preference for some ponds over others. Habitat features such as pond construction and design, the presence of submerged vegetation, vegetation along the shore and reed beds, and pond area correlated with occupation frequency and might be considered to be indicators of pond quality. Ponds were occupied sequentially from best to worst. Thus, when the population size increased, the number of low-quality ponds occupied also increased. High-quality ponds held more breeding pairs than low-quality ones, resulting in the mean reproductive success per breeding pair being independent of pond quality. Little Grebes therefore occupy ponds in a manner consistent with the expectations of the IFD model.

Bonelli’s Eagle Aquila fasciata is one of the rarest birds of prey in Europe, where it has suffered a significant decline in recent decades. We present information on the homeranges and spatial parameters of 18 Bonelli’s Eagles radiotracked in 2002–2006 in Catalonia (northeast Spain) and describe the home-range probability kernel, distances moved, breeding area eccentricity, territorial overlap, nearest neighbour distance and breeding site fidelity, and assess the influence of sex, breeding status, season and geographical area on these parameters. Median home-range according to the minimum convex polygon (MCP) and 95% kernel were 50.3 and 36.1 km 2 , respectively. The median breeding area eccentricity was 1477 m. There was considerable overlap in the home-range of both sexes within pairs (MCP: 71.4% and 95% kernel: 98.5%), indicating close pair bonding and similar foraging patterns. Overlap in home-ranges of up to 15% between neighbouring individuals also occurred and was positively related to breeding pair density. There was no difference in spatial parameters between sexes or with breeding status, but during the non-breeding season Eagles had larger home-ranges and stayed further from nests. The high consistency across birds suggests a pattern of spatial use that is characteristic of this species. The high level of use of breeding areas and their surroundings (50% kernel) throughout the year makes it important that these areas be protected from human disturbance. Additionally, it is necessary that heavily used areas away from nesting sites, which are used for foraging and roosting, are identified, protected and managed in a sustainable fashion.

By 1974, the Mauritius Kestrel Falco punctatus had declined to only four known wild birds, including one breeding pair, as a result of habitat loss and pesticide contamination. A conservation project begun in 1973 has used many management techniques including captive breeding, supplemental feeding of wild birds, provision of nestboxes, multiple clutching, egg pulling, artificial incubation, hand rearing and release of captive-bred and captive-reared birds by hacking, fostering and predator control. A total of 331 kestrels were released in the 10 years up to the end of the 1993–1994 breeding season; one-third of these were captive bred, the rest were derived from eggs harvested from the wild. About 257 (78%) released birds survived to independence and 61% of independent juveniles survived their first winter. Although at least 71% of ringed birds attempted to breed in their first year, only 38% of the nests of first-year females successfully fledged young, averaging 1.7 per successful nest. Older females fledged young from 64% of nests, fledging an average of 2.0 per successful nest. The breeding success of hacked birds was similar to that of parent-raised kestrels, though the clutches of hacked birds tended to be larger. Annual replacement of birds holding territories averaged 17% for both sexes. By the 1993–1994 season, an estimated 56–68 pairs had established territories in the wild with a post-breeding population, including floating birds and independent young, of 222–286. Most of the kestrels were in three sub-populations, two of which were derived entirely from released birds. Mauritius Kestrels are relatively sedentary; 89% of ringed birds found nesting were less than 5 km from their release or Hedging site. Since the pesticides responsible for their decline are no longer used, the number of Mauritius Kestrels should continue to rise through natural recruitment. The distribution of suitable habitat suggests that an eventual population of 500–600 kestrels on Mauritius is possible. Due to its outstanding success, the release programme for the Mauritius Kestrel ended after the 1993–1994 breeding season, though the population will continue to be monitored carefully for at least the next 5 years.

Population density and intra- and interspecific competition of the African Fish Eagle Haliaeeetus vocifer were studied in Kyambura Game Reserve, southwest Uganda. Density varied significantly between 1.75 and 3.25 individuals per km of shore for the breeding biotopes along the Kazinga Channel and crater lakes and between 0.45 and 0.58 for unsuitable biotopes such as the Kyambura Gorge or the bush grassland. The age-class distribution showed extremely high percentages of immatures in these unsuitable biotopes (50–95%) as a consequence of intraspecific competition for space and food. Some immatures survived in the bush grassland, feeding on lion and leopard kills and very possibly on birds. Each territory was up to five times larger than breeding pair territories along the Kazinga Channel (5.1 km2 in comparison with 0.9 km2). Interspecific competition for space was likely between immature African Fish Eagles and other species of raptors. Ecological segregation with regard to space was assessed between these species in the bush grassland.

SUMMARY 1. The behaviour of the Little Penguin Eudyptula minor was observed at Cat Island, Bass Strait during the 1957/58 nesting season. 2. Although the birds have a number of natural enemies, man is probably the most serious destructive agent in this area at present. 3. The bird's repertoire includes contact notes and “songs”, the latter as an accompaniment to a variety of display postures. 4. During the stage when the chicks are guarded they are fed by the relieving adult soon after its arrival in the burrow, the young one's head being plunged into the parent's mouth. During “guard” and “post-guard” stages the chicks studied were fed by only one adult bird although both might return to the nest. 5. The chicks begin to emerge after dark from their burrows at about 23 days old. One was deserted at 56 days and left for the sea at 60 days. 6. Display includes a variety of postures many of which seem analagous to those described by workers on some of the New Zealand and Antarctic penguins. A special dance precedes coition and trumpeting displays seem to serve for advertising territories and for threat. There is a welcome ceremony and ceremonial mutual preening. 7. Coition is frequent during the nesting period and recurs later when the penguins return to their burrows to moult. 8. Both old and young spend much time preening and collaborate in this activity. 9. Unemployed single birds were the first to moult. One breeding pair returned after 41 days post-breeding sojourn at sea, completed the moult and returned there after 18 days without food.

The Siberian Tit Parus cinctus population of Finland, and probably of the whole of Fennoscandia, has declined dramatically during this century. Understanding its population dynamics is essential for its conservation. We studied annual survival rate and dispersal distance of both breeding and fledgling Siberian Tits during 1989-97 in a moderately managed forest habitat near the southern border of its range in Kuusamo, northeastern Finland. Breeding density was low, averaging 0.51 pairs/km in a nestbox area of about 42 km2. This was probably an underestimate, because we did not search for nests in natural holes. However, following its population decline, overall densities at the southern border of the range are low. The study area was, however, suitable breeding habitat as reflected by their high nesting success. Brood size at fledging averaged 7.45 young, and reproductive output was 6.16 young per breeding pair, including failed nests. Clutch size adjustment was successful among pairs producing fledglings because, on average, 92.6% of the eggs laid produced young in successful broods. Median distance between consecutive breeding attempts was 100 m for both males and females (range 0–2500 m and 0–6000 m, respectively). Natal dispersal distance was significantly longer in females than in males. We applied Cormack-Jolly-Seber modelling to estimate survival and recapture probabilities separately. Survival of breeding birds was not sex-related, averaging 0.69 annually. Some of the ringed fledglings (3.0%) were later captured as breeders in the area. This is an underestimate of local survival rate due to incomplete recapturing of breeding birds. The implications of these results with respect to the conservation status of the species are discussed.

Summary. This paper summarizes observations on territorial behaviour in the Great Crested Grebe in Oxfordshire and Berkshire and compares them with those of Venables & Lack (1934, 1936) in Surrey. On all waters, each breeding pair defended at least the immediate nest-site but the area of the defended water adjoining this varied considerably. Such variation is probably affected by population density, distribution and availability of nest-sites, the topography and the frontage of water before each nest-site, as well as the degree of aggressiveness of individual pairs. The territories are taken up by already mated pairs and are often deserted when the young hatch, but a few pairs stay in the territory with the brood. More observation is needed on “colonialism” in the species because it appears to vary locally. Some possible functions of territorial behaviour are discussed but no definite conclusions can yet be drawn.

Summary Nestling survival and nestling weights in P. domesticus and P. montanus were studied in 1961 and 1963–64 at Oxford. This paper concludes a study of factors influencing the reproductive rate. Taking all losses into account, P. domesticus reared an average of 1.6 nestlings per brood (45%) and P. montanus 2.7 nestlings per brood (59%). About a third of all broods of both species failed completely to survive the nestling period. In P. domesticus these failures were most numerous in the middle part of the breeding season and are attributed to nutritional deficiencies derived from unsuitable food provided as a consequence of a seasonal food shortage, but in P. montanus complete brood failures occurred mostly in the second half of the nestling period and are attributed to predation. 43 broods of P. domesticus and one brood of P. montanus were weighed daily. Those of P. domesticus were classified as (1) successful broods—in these some nestlings died in the larger brood-sizes, apparently through starvation; (2) long-lived unsuccessful broods—in these the nestlings died at intervals and failure was attributed to nutritional deficiencies; and (3) short-lived unsuccessful broods. A slight decrease in the weights of nestlings in successful broods at the end of the nestling period is attributed to the utilization of insulating fat facilitated by the completion of the feather covering. Nestlings of both species left the nest at 88–89% of the adult weight. Taking all “successful” broods together, the percentage survival rates on nestling day 131/2 (day of hatching = day 1/2) in P. domesticus were 81–82% in b/2–3, 70% in b/4 and 56% in b/5 (a situation paralleled in this respect by P. hispaniolensis), but in P. montanus they were c. 82% in all brood-sizes. Hence, in P. domesticus b/4 probably gave rise to the largest number of nestlings reared per brood, while in P. montanus most nestlings were produced by the largest brood-size. Weighings of many broods on day 131/2 showed two trends in the weight of the nestlings: (1) in both species the weight of the nestling decreased as the number of survivors from each initial brood-size decreased; (2) between successive initial brood-sizes the weight of the nestling of P. domesticus decreased with increasing brood-size but in P. montanus there was no change. The losses in the larger broods of P. domesticus occurred mostly in the first half of the nestling period—apparently in association with the asynchronous hatching of the eggs and as a consequence of the limitation on the feeding frequency of the adults. Nestling survival was lowest in the larger broods in the middle of the breeding season and contrasted with the mid-season increase in mean clutch-size. It is suggested that in the study area there was a (possibly unnatural) shortage of food suitable for nestlings in the middle of the season. It is suggested that in P. domesticus the unexpectedly low feeding frequencies of the adults with large broods, apparently causing their low survival rates, may be an adaptation evolved to obtain the maximum amount of food in the presence of other adults which would be attracted to a food source by higher rates of activity. The breeding success calculated from data derived from the whole of this study was 35% for P. domesticus and 49% for P. montanus (2.9 and 3.9 nestlings per breeding pair per year respectively). It is suggested that the population of P. domesticus was much closer to a critical limiting factor, e.g. food supply, than that of P. montanus. This may account for the striking differences between the two species in their nestling survival rates and their nestling weights in relation to brood-size; in particular, the success of the larger broods of P. montanus may have been a temporary phenomenon.

The breeding ecology of Clay-coloured Robins Turdus grayi was studied in 1979 in the former Canal Zone of lowland Panama. Two study areas were chosen close together, Summit Gardens (27-3 ha), an ecological island of habitat suitable for Clay-coloured Robin surrounded by forest, and Morgan's Gardens (3–6 ha), a similar island surrounded by deforested areas and settlements. Eighty-three active nests were found and checked. The breeding season lasted from 2 March to 21 June. In Morgan's Gardens the first broods were raised in the dry season and second broods in the rainy season; in Summit Gardens most broods started at the beginning of the rainy season. In comparison to the closely related Blackbird T. merula in Poland, Clay-coloured Robins build nests on isolated trees or bushes, usually in more conspicuous sites (interpreted as an anti-predator adaptation) and on flexible, horizontal branches off the main trunk. Over 45% of broods were destroyed by predators but other factors causing brood loss were negligible. Nests built on palms were considerably safer. In the dry season the predation rate was low (5%) and increased during the course of the rainy season. Unlike Blackbirds, Clay-coloured Robin nestlings were given a lot of fruit; their diet was diversified. Starvation occurred in 60% of nests although usually only the youngest nestling died. Breeding density in Morgan's Gardens at 50 pairs per 10 ha was much higher than in Summit Gardens at 15>8 pairs per 10 ha. Breeding losses were lower, the nestlings were fed more fruit, the average nestling weight was lower and the production of fledglings per breeding pair was twice as high in Morgan's Gardens. It was concluded that a strategy of settling in a rather overpopulated place with hard foraging conditions but lower predation was better than settling in a area with a better food supply but higher predation.

Upland Geese Chloephaga picta were studied between 1977 and 1980, primarily around Darwin, East Falkland, in order to describe their breeding biology, moulting and adult survival. The population of breeding birds in a valley reached a peak from mid-September to late November when nesting took place. The average territory length was 240 m in five valleys. Breeding adults generally returned to breed in the same territory each year and with the same mate. Nests were on the ground, usually amongst whitegrass Cortaderiapilosa. The mean clutch size was 6-1, brood size was 5-1 and fledged family 3–9. Incubation took 30 days and the fledgling period was about 70 days. Most broods were raised in the nesting territory. Growth of goslings is described. The breeding success between laying and fledging was 0–34 (in 1977) and 0–29(in 1978), giving an annual production of 21 and 1–8 young per breeding pair. Fledglings remained in family parties through the autumn and winter and were evicted by their parents in early spring. Some siblings stayed together for short periods and then joined other non-breeders. Females started pairing at ten months of age and most were paired at 17–18 months. Some bred for the first time at 23 months. Males started pairing at about 20 months of age. Flightless moult (shedding) took place at ponds or in sheltered inlets of the sea, in flocks of up to several hundred birds. Flightless birds were found between 14 November and 11 February, though 50% were flightless between 26 November and 2 January. Individuals were flightless for 36 days. First-year birds were more synchronized in shedding than adults. The percentage of first-year males (in the male component) varied from 16-5 to 45-9% in shedding flocks, and significantly more males were present in some flocks. The flocks were composed of first-year and second-year birds too young to breed and failed breeders. The percentage of a shedding population which returned to the same site in successive years was 25-3 and 15-1% at two localities. The moult of other feather tracts is described. The annual survival rate of breeding adults was 82%. A model of the population dynamics is presented. The current level of culling to control the goose population is less than the number which must die each year to maintain a stable population.

Summary. 1 The Blackbird Turdus merula has now bred on Shetland for about 70 years and colonized all but four of the inhabited islands. A few isolated territories occur in the hills. 2 Of 204 occupied nests 50% were inside buildings, 19% in stone walls and 18% in garden vegetation, all indicating man's importance as a precursor. Inside nests were used repeatedly; this may have survival value, enabling a third brood to be reared. 3 Breeding density, estimated over 9 square miles for three. seasons, was ca. 1 pair to 300 acres which would produce a total Shetland breeding population of roughly 1230 pairs. Territories were not usually contiguous and a breeding pair would often roam over ca. 40 acres. 4 The egg-laying period (April-July) is later than in England and breeding changes such as song and beak colour are correspondingly delayed. There is no autumn or winter song. 5 The average of 117 clutches was 4.32, which is significantly higher than the average (3.9) for 483 British nests. The origin of this difference is discussed. Average brood size, nesting success and breeding curves are given. 6 Of 403 nestlings ringed, 237 also carried colour rings. Returns and sight records over four years show that the young birds remain in or near the parent territory until 6–7 weeks old, then establish themselves in an area providing food and cover where they remain all winter. First-winter returns are all within 5 miles of the nest. About March a further move is usually made to establish a breeding territory. Of eleven ringed birds located breeding, seven were within 1 mile of the parent nest, and in three cases the new breeding area was adjacent to the parent territory. Both sexes may winter in their breeding territory and isolated males often defend winter territory. As yet there have been no recoveries outside Shetland though birds over a year old have moved up to 31 miles to other islands in Shetland. 7 Dates and pattern of the spring and autumn passage are given, together with the ringing returns available. These show that Blackbirds from Norway and Denmark pass through to wintering grounds in Britain, while others from the same source remain in Shetland all winter. 8 Comparing the wintering population with that of summer we find a greater concentration round the crofting townships, total numbers are higher and the ratio is weighted in favour of males. Winter Blackbird figures from elsewhere in Britain suggest that this preponderance of males is more widespread.

The reproductive biology of the endangered Ouvea Parakeet Eunymphicus cornutus uvaeensis, an endemic subspecies of Ouvea island (Territory of New Caledonia, Southwest Pacific) was studied from June 1994 to February 1996. Breeding was recorded from early August until late January. All nests were sited in cavities of native forest trees, 90% of them in Syzygium sp. and Mimusops sp. Mean clutch size was 2.9 eggs (range 2–3), and double clutches were recorded. Incubation lasted 21 days and the nestling period averaging 43 days. An average of 1.65 chicks fledged per nest but only 0.75 per breeding pair were still alive 30 days after fledging. The main causes of chick loss were starvation of the third sibling during the first week due to hatching asynchrony, raptor (presumably Brown Goshawk) predation of fledglings and human harvest for the pet trade. Growth curves and multiple regressions of weight, culmen-width and -length, tarsus- and wing-length, showed that wing-length was a good predictor of age, and that there were significant differences between the sexes for weight and culmen-width. The pattern of the breeding season, brood reduction, nest-site characteristics and presumed size of breeding territories suggest that both food and availability of suitable nest-sites may be factors limiting breeding productivity. Proposals for conservation of this endangered bird are presented.

The breeding biology of Black Guillemots Cepphus grylle was studied from 1982 to 1984 in Shetland, on islands lacking introduced mammalian predators. Adult survival (94%), clutch size (1.75-1.92) and breeding output (1.05-1.34 young fledged per breeding pair) were very high, indicating that conditions were relatively favourable on the islands studied. The timing of breeding varied significantly between years and was somewhat later than in other temperate parts of the range. In 1984 food was probably more readily available (possibly due to better weather conditions) in the pre-breeding period, which enabled more inexperienced birds to reach the condition threshold for breeding. It is likely that these birds tended to lay single-egg clutches in more open sites which were more susceptible to egg predation by crows. Nest-site quality and food availability were the key determinants of breeding productivity.

The social organization and behaviour of the Hoatzin Opisthocomus hoazin, a cooperatively-breeding folivorous bird, was studied in the central plains (llanos) of Venezuela. In this area Hoatzins nested in communal social units of two to eight individuals. Units were usually composed of a breeding pair and up to six helpers at the nest. Helpers, usually offspring retained from the previous years' nesting, aided in all breeding activities of their social unit except egg production. On the study site, Hoatzin units defended extremely small, all-purpose territories along watercourses during the rainy (breeding) season, but migrated up to 2 km to areas with permanent water during the dry season. Nesting extended from early May to October. Nest and egg measurements and growth rates of young are provided. Nesting success was low (27%), primarily due to predation by Cebus olivaceus and several other species. Annual survival of adults and young was high. Young did not breed during their first year; 90% of yearlings remained on their natal territories as helpers. Females appear to be the dispersing sex. The results are discussed in relation to previous work on the Hoatzin. The demography of the study population fits the criteria for several recent theories regarding the evolution of cooperative breeding in birds.

Summary In the colony-nesting bee-eater Merops bulocki of the northern savannas of Africa males preponderate in the proportion 1 -5 to 1 female, initial breeding occurs at varying ages, and adults of both sexes and all age classes, particularly one-year-old males, assist breeding pairs with nest excavation, incubation, and provisioning the pulli and fledglings. Up to three helpers can occur at one nest, and they may be siblings of a previous year's brood. Pair-bonds are for life, and bonds formed between the breeding pair and their helpers may endure until next season. Some evidence suggests that other gregarious open-country bee-eater species are similar in these respects but that forest and solitary-breeding savanna species have the sex ratio at parity and do not breed co-operatively. Breeding dispersion of savanna species is related to specific size, the largest (which forage most widely) nesting in the densest aggregates. Other instances of birds with comparable social organisations are briefly reviewed. The 80 species involved comprise broad systematic and ecological spectra and about 60 of them inhabit hot climates in America, Africa and Australia. It is suggested that co-operative breeding provides a reserve of experienced individuals whose recruitment to breeding permits (1) fine control of stable populations in non-seasonal habitats (tropical forest) within the capacity of the food resources; (2) crude adjustment of fluctuating populations in habitats with unpredictable rainfall (Australia), enabling them rapidly to recuperate from depression and to achieve the highest population level the improved food resources can sustain; and (3) regulation of populations in intermediate habitats (tropical savannas) by either means according to the dictates of immediate ecological circumstances.

The breeding success of 18 groups of Arrowmarked Babblers Turdoides jardineii was followed in the 1992–1993 breeding season. The first eggs were laid in late October 1992 and the last eggs in February 1993. Group size was positively correlated with territory size. However, neither group size nor territory size was correlated with the number of offspring raised by a group. Extra adults in a group may not have enhanced the reproductive output of the breeding pair, but they helped in the defence and enlargement of a territory in a saturated habitat.

Finding the most biologically meaningful scale at which to describe environmental variation is a persistent problem in ecology. Most studies of forest passerines are conducted at the scale of the habitat or woodland and do not account for environmental variation between individual breeding sites. Here we employ two GIS models, and four spatial scales, to describe environmental variation among 4683 Great Tit Parus major breeding sites occupied over a 32-year period in Wytham Wood, Oxford, UK, and use these data to help explain variation in an environmentally sensitive trait, first egg date. Model 1 used Thiessen polygons to generate individual spatial scales for each breeding pair, while Model 2 used a range of predetermined radial scales around each breeding site. Environmental variables included local altitude and aspect estimated from a Digital Terrain Model, and the number of Oak Quercus robur trees around each nest-site, used here as a surrogate for local food (caterpillar) availability. In a Linear Mixed Model, Model 2 explained the most variation in lay-date at a scale of 25 m from each nestbox. However, the model that returned the lowest Akaike Information Criterion (AIC) contained environmental variables from Model 2, but measured at different fixed spatial scales of between 25 and 75 m. Results from this final model showed that birds breeding in low-altitude, north-facing and Oak-rich areas bred earlier than those in high-altitude, south-facing and Oak-poor areas, at radial scales of 25, 75 and 75 m from each nestbox, respectively. In addition, birds in interior sites bred earlier than those nearer the woodland edge, although this edge effect was only apparent on north-facing slopes. Thus, the current study demonstrates that a range of GIS models can be effectively used to scale and describe environmental variation between individual breeding sites, and that fine-scale topographic variation, food availability and edge proximity can affect the breeding date of Great Tits.

Mass loss of chick-rearing birds can be the direct consequence of physiological stress (reproductive stress hypothesis) or an adaptive mass adjustment in response to the increased demands on flight efficiency during the flight-intensive chick-rearing period (adaptive mass loss hypothesis). To test which of these hypotheses best explains mass loss in South Polar Skuas Stercorarius maccormicki rearing chicks, a food supplementation experiment was carried out in the austral summer 2000/01 at King George Island, Antarctica. Half of the breeding pairs were fed about 20% of the chick's daily energy demand every second day and chick growth and adult nest attendance were recorded. Parents were caught at the start and the end of chick-rearing to calculate adult mass loss. Male parents of food-supplemented pairs attended their nest territories more than control males but females kept their attendance constant. Chick growth was only minimally affected and the treatment probably had no fitness consequences. Male Skuas in control pairs had a higher deviation from the body size-mass regression at the end of chick-rearing compared with the start, supporting the stress hypothesis, whereas female deviation remained unchanged. Males of food-supplemented pairs were heavier than unsupplemented males at the end of the breeding cycle but not significantly so. Food-supplemented females were lighter at the end, supporting the adaptive mass loss hypothesis. Adult mass loss is thus best explained by the reproductive stress hypothesis in males but by the adaptive mass loss hypothesis in females. However, the two hypotheses are not mutually exclusive and the results do not exclude the possibility that mass loss in females is stress-induced but the amount of mass lost is an adaptive adjustment to the reliability of the food supply. The finding that members of a breeding pair may follow different strategies of mass adjustment has implications for the use of mass loss as an index of parental effort. Without knowing which strategy each sex has adopted it is of little use to compare mass loss between parents.

The Yellow-legged Gull Larus cachinnans was first recorded in Poland in the 1980s. We analysed the probable factors responsible for its successful colonization of new areas. We also expected that such a large species should affect populations of other colonial waterbirds. We studied the breeding and feeding ecology in the largest inland colony of the Yellowlegged Gull in Poland, located in a sedimentation basin near Tarnow (southeastern Poland). The first breeding pair was recorded in 1992 and the population reached 177 pairs in 2001. The population growth rate in this colony, of about 58% per year, fits an exponential model. Nine localities with breeding pairs have been found recently in southern Poland and we now estimate the total population size to be 200‐250 pairs. The large clutch size, and high hatching and breeding success in the Tarnow colony suggest that food was plentiful. Food items were frequently found at the nests. Fish, mainly Carp Cyprinus carpio , were the predominant food items delivered to chicks; however, there was more refuse brought to nests during the incubation stage. Immigration probably caused the growth of the colony studied, although our calculations have shown that natal productivity alone is sufficient to maintain this population. The study showed that the growing population of Yellow-legged Gull might cause considerable reduction in the population sizes of some of the native waterbird species. Many hypotheses attempt to explain the range size and distribution of species (Lawton 1993, Brown et al . 1996, Gaston 1996, Kirkpatrick & Barton 1997, Sagarin & Gaines 2002). It is believed that populations in the centre of the range occupy habitat of better quality and have a higher intrinsic rate of growth than those at the range margin (Lawton 1993). However, as populations of some species have increased rapidly, others have become vulnerable to extinction, and this is often associated with boundary range changes. Finding the factors that affect these changes is important in understanding the processes occurring in populations at a species’ geographical boundary; this may be crucial for predicting the effects of population growth in invasive species, and may be

As a result of opposing selective forces, the external strength of avian eggs should be near some size-specific optimum. However, in certain situations there should be selection on females to lay unusually strong eggs. According to one hypothesis, intraspecific egg destruction should favour increased egg strength as a means of defence against conspecific intruders. This hypothesis predicts that House Wrens Troglodytes aedon, a species well known for its tendency to destroy conspecific clutches, should be under selection for unusually strong eggs. However, the intensity of selection for strong eggs should also be modified by efficacy of nest defence against conspecific intruders in a given species (i.e. efficient nest defence by the breeding pair should weaken selection for unusually strong eggs). The goals of our study were: (1) to establish whether House Wren eggs are stronger than expected for their size; (2) to determine which structural mechanisms are responsible for their unusual strength; and (3) to test a hypothesis that, between wren species, the efficacy of nest defence and the intensity of egg-destroying behaviour affect the intensity of selection for unusually strong eggs. Our results demonstrated that: (1) House Wren eggs are 1.9 times stronger than expected for their size; (2) their unusual strength is achieved mostly by their unusually thick shells; and (3) eggs of the House Wren (extensive paternal nest defence; male egg-destroying behaviour suppressed during incubation) are significantly weaker structurally than eggs of the Marsh Wren Cistothorus palustris (reduced paternal nest defence; male egg-destroying behaviour present throughout incubation). These results are consistent with the hypothesis that the intraspecific egg-destroying behaviour and the efficacy of nest defence by the breeding adults have played a role in the evolution of strength of House Wren eggs.

The continental African Reed Warbler Acrocephalus baeticatus, like its relative the Seychelles Warbler Acrocephalus sechellensis, breeds in isolated patches. We studied the mating system of the African Reed Warbler to see whether this species, like the Seychelles Warbler, shows co-operative breeding. The African Reed Warbler is not polygynous. The majority breed monogamously (88Y0, n = 65), however in 12% of the territories three adult unrelated birds (mostly males) were observed participating in the brooding and feeding of nestlings, suggesting a polyandrous breeding system. Multilocus DNA fingerprinting revealed that the helping bird was unrelated to the pair birds. The percentage of nests with helpers was low compared to rates found in the Seychelles Warbler or Henderson Reed Warbler Acrocephalus vuughani taiti. This could be due to the scarcity of potential helpers or to the fact that, although limited, birds still had the opportunity to disperse within a meta-population structure in search of vacant territories. The presence of helpers was associated with increased hatching success due to lower predation rates, but not with increased fledging success. Another possible benefit of helping behaviour in this species could be improved predator detection and mobbing. Nest predation was high and warblers tended to build their nests in the highest, most dense reed patches available in their territory. There was no relation between habitat quality, measured as insect food availability, and the occurrence of helpers. Co-operative breeding is a reproductive system in which individuals other than the main male-female pair also exhibit parent-like (‘helping’) behaviour toward young of a single nest or brood. Numerous variations have been identified including helping at the nest by non-breeding offspring that delay dispersal and remain with their parents, and various forms of cooperative polygamy or plural breeding in which more than a single male or female share breeding status within the same social unit. Helping generally consists of feeding nestlings or fledglings, but can also include incubation and nest or territorial defence (Brown 1987). Co-operative breeding, where more birds than just the breeding pair raise the young, occurs in about