Expansion of the Mediterranean Gull Larus melanocephalus in Poland

Since 1981, when the first breeding pair of Mediterranean Gull Larus melanocephalus was recorded in Poland, the population of this gull has increased considerably. Its population size was stable until 1997, not exceeding ten pairs annually; thereafter, an increasing number of sightings were made, and during the last 5 years between 26 and 39 breeding pairs have been recorded in Poland. To date, breeding sites have been established in a total of 45 sites (maximum of 19 sites in a given year), with 27% of these (43% of all broods) found on islands located in the middle course of the Vistula River. Breeding sites have also included artificial reservoirs, such as dam reservoirs (20% of sites, 19% of broods), gravel pits (9% of sites, 13% of broods) and fishponds (24% of places, 8% of broods). Mediterranean Gulls were found to nest only within the colonies of other Laridae. Single pairs were recorded at 40% of the breeding sites, whereas a maximum of two to five pairs were recorded at 47% of the other sites. The great majority of breeding attempts were recorded in Black-headed Gull L. ridibundus colonies. In two cases, Mediterranean Gulls bred within mono-specific colonies of Common Gulls L. canus consisting of 60–150 pairs. The biggest concentrations of breeding sites were along the middle course of the Vistula river and in the southern part of Poland.     

Explaining annual fluctuations in breeding density of fieldfares Turdus pilaris– combined influences of factors operating during breeding, migration and wintering

In a subalpine birch forest in Central Norway, the breeding population of fieldfare Turdus pilaris varied from 3 to 63 pairs per km² during 1966–2000. For the period 1971–1995, the breeding density was negatively related to the number of days with >75% snow covered ground in April, presumably because snow cover reduce the availability of earthworms. In a multiple regression model for the period 1974–1995, snow cover in spring, the number of migrating fieldfares observed at two ornithological stations at the southern coast of Norway in April, the mean temperature in November in the preceding year, winter temperatures, rowanberry production in the previous autumn, and the interaction effect of the two latter variables (high value of one of these variables reduced the negative effect of a low value of the other) explained 80% of the variation in fieldfare breeding density. Autumn and winter temperatures, as well as rowanberry production, contributed through a positive effect, probably because these factors affected the number of fieldfare present in Norway throughout winter, which in some years may constitute a significant proportion of the overall fieldfare population.     

Reproduction and survival of Glaucous Gulls breeding in an Arctic seabird colony

ABSTRACT.   Despite being widespread and easily observed, little is known about the life history of Glaucous Gulls ( Larus hyperboreus ). From 1984 to 2007, we examined their breeding biology and demography at Coats Island, Nunavut, Canada, where they nest alongside a colony of 30,000 pairs of Thick-billed Murres ( Uria lomvia ). The gulls fed mainly on murre eggs and chicks and by scavenging adult carcasses. The median age at first breeding was 5 yr, and the mean age was 4.8 ± 0.9 yr. Adult survival was estimated as 0.84 ± 0.03 (SE). The mean clutch size was 2.56 eggs and the mean number of young reared per year was 1.6 (range = 0.9–2.2). Birds reared at the colony provided 40% of recruits. Assuming that survival of locally reared chicks that emigrated was similar to that of chicks that returned to the colony, about 22% of the young gulls survived to breeding age. The timing of breeding by Glaucous Gulls appeared related to the timing of laying by murres. Although the demographic characteristics of Glaucous Gulls in our study were similar to those of populations of other large gulls, adult survival was at the lower end of the range for populations of large Larus gulls. There is some evidence that Glaucous Gulls exhibit lower survival than large gulls breeding in temperate areas, possibly because of contaminant burdens. In general, however, the demographic characteristics of large gulls show little variation and are probably a product of their common phylogeny.     

Habitat selection and breeding success in Yellow-legged Gulls Larus cachinnans

The habitat selection and breeding performance of Yellow-legged Gulls Larus cachinnans were studied in the Medes Islands colony, northeastern Spain, during 1995 and 1996. Of the three main habitats on the islands (shrubs, grass and bare areas), gulls first occupied those with the highest percentage of tall vegetation. Gulls tended to select nest sites with 20–75% cover despite great differences in the cover in the habitats and territories, suggesting that the presence of a suitable nest site may play a major role in the choice of breeding habitat. Nest-site tenacity did not influence the preferences of gulls at any level since the same pattern of choice was observed in an area subjected to annual culls (i.e. where most of the breeding pairs were culled annually and replaced by naive birds). In spite of great differences in the physical characteristics of the habitats, little difference was found in breeding performance of the gulls between habitats. Gulls nesting in the least preferred habitat (i.e. mainly bare) had smaller clutches than those nesting in the other two habitats, possibly as a result of their later seasonal laying. Despite the similar breeding success in different habitats, gulls did not seem to distribute according to the ideal free model reported for Herring Gulls Larus argentatus since the density in the preferred habitat (i.e. shrubs) was never higher than in the other two. We suggest that the habitat selection by Yellow-legged Gulls within the colony could follow an ideal despotic distribution.     

The Sooty Falcon Falco concolor on the Red Sea coast of Saudi Arabia: distribution, numbers and conservation

Ground and aerial surveys of breeding Sooty Falcons Falco concolor were conducted along the western coast of Saudi Arabia and its offshore islands from August to October 1991 and 1992. An estimated population of 260–381 pairs was found. The known world breeding population is still below 1000 pairs. Most rocky islands were occupied except the largest islands of the Farasan archipelago. Among the many low islets surrounded with mangrove, only one small group near Al Lith harboured breeding Sooty Falcons. The distribution pattern, density and breeding success of the falcons seemed to be strongly influenced by food availability (autumn migration of small and medium-size birds) and the deterring presence of terrestrial predators. Human disturbance and trapping are still of local importance.     

辽宁双台河口黑嘴鸥的迁徙模式与种群生存率

1996-2008年6月份,对辽宁双台河口国家级自然保护区黑嘴鸥使用特定编码的彩色旗标,共标记2820只。其中成鸟31只,幼鸟2789只。根据23个越冬地点2729条彩色旗标的重见记录,推测辽宁双台河口黑嘴鸥的迁徙路线主要有两条:一条向东迁徙至韩国西南沿海及日本西部沿海越冬;另一条向南迁徙至我国天津以南的东部沿海,包括台湾西部沿海越冬。依据1996-2007年双台河口标记的黑嘴鸥幼鸟当年在日本西部沿海重见记录,计算12a间其相对生存率为(7.77±4.00)%(1.67%-14.89%)。其中1997、2001、2004、2006和2007年的相对生存率均低于平均水平,特别是2006年达到12年来的最低值(1.67%)。采用MARK软件中的Cormack-Jolly-Seber(CJS)模型,估计黑嘴鸥亚成体和成体的年生存率分别为0.613±0.058和0.746±0.042,重见率分别为0.897±0.04和0.799±0.053。亚成体较成体的重见率高,可能与亚成体到达越冬地相对比较集群有关。同时建议开展更多的彩色旗标观察活动,便于进一步了解同一越冬地中不同年龄段黑嘴鸥的移动规律。     

INTRASPECIFIC PREDATION AND COLONIAL BREEDING IN LESSER BLACK-BACKED GULLS LARUS FUSCUS

The breeding biology of Lesser Black-backed Gulls was studied on Skokholm Island, Pembrokeshire, where the number of breeding pairs has been increasing at about 20% per annum since 1963. Laying was found to be synchronous within small groups. Clutch size and breeding success showed seasonal declines over the spread of breeding. The loss mainly of eggs, but to a lesser extent of chicks also, caused this overall decline in success. Hide observations indicated that the bulk of these losses arose through predation by nesting adult Lesser Black-backed Gulls on their nearest neighbours. Not infrequently the protagonist had lost its own clutch shortly before turning predator, and such a chain-sequence should lead to a steady build-up of aggressive failed breeders and so account for the observed seasonal increase in egg loss. Attentiveness to the clutch decreased with season but this was unlikely to have been important in precipitating the predation. Intermediate plant cover was associated with highest nest density and also with highest chick survival. In addition, nest density was directly correlated with chick survival. Whether plant cover and nest density separately affect chick production remains unresolved. Nevertheless, the increasing nest densities in this colony caused by the growth of the gull population are thought to be responsible for the widespread intraspecific predation, the intensity of which is probably a new feature of the gulls' breeding behaviour. The implications of this 'internal' predation for laying synchrony and aggregated nesting are discussed; these two factors of the breeding pattern probably evolved largely to combat 'external' predators. Not only are they no protection against inter-neighbour predation but appear to facilitate it. It remains to be seen whether this kind of predation will significantly affect breeding patterns with further increases in nest density.     

Prey abundance and reproductive success of the golden eagle Aquila chrysaetos in Sweden

Reproductive output of the golden eagle Aquila chrysaetos (L.), was studied in two areas within the species distribution in northern Sweden during 1975–1980. Reproductive success was compared with the abundance (based on hunting bag statistics) of small game prey species and with the microtine cycles. The proportion of golden eagle pairs with successful breeding and the number of young produced per occupied territory varied greatly between years (21–85% and 0.27–1.24, respectively). In the northern study area I found a significant correlation between the proportion of pairs with successful breeding versus total hunting bag of small game species. There were also significant correlations between vole density and breeding success one year later. This was not the case in the southern study area, mainly due to a good reproductive year for golden eagles in 1977 when small game species were scarce. The good reproductive output in 1977 may be explained by favourable weather conditions that spring. Whether breeding occurs or not is probably determined by prey abundance early in spring just before the golden eagle female lays her eggs.     

Variation in the abundance of Red-breasted Mergansers Mergus serrator on a Scottish river in relation to season, year, river hydrography, salmon density and spring culling

Red-breasted Mergansers Mergus serrator were counted in the river North Esk, Scotland, and on the sea nearby, 1987–1990. Pairs arrived at the river estuary from early winter, but the main influx to freshwater took place in late April and in May, when breeding pairs dispersed far upriver. Females began incubation from late May. Most young hatched in July and fledged by late September. Males left the river in June and congregated at an offshore moulting site, their numbers peaking in August, and dispersed rapidly in September.
Breeding density and total duckling production decreased with increasing distance upstream, decreasing river width and increasing gradient and elevation. The total number of breeding pairs and their distribution on the river were similar from year to year, despite variable numbers killed, suggesting a stable breeding population near the upper limit the habitat would support in those years. It also suggested that killing mergansers in April was an ineffective way to reduce the population. The spatial variation in merganser breeding density was not correlated with the density of their main spring food, parr of salmon Salmo salar , but could have been related to its availability.
The production of well-grown ducklings varied annually and was inversely correlated with river flow during the main period of hatch. It is argued that Red-breasted Mergansers breed late in the year because the hatching of ducklings in July coincides with an abundance of their food, large aquatic invertebrates and tiny juvenile fish.     

The Storm's Stork Ciconia stormi in Indonesia: breeding biology, population and conservation

Storm's Stork Ciconia stormi is one of the rarest of the storks, regarded as globally endangered and found only in parts of western Indonesia, Malaysia and Brunei. Prior to this study, its breeding biology was unknown and the population status in Indonesia was not well understood. Its breeding habitat, prey, behaviour, voice, eggs and the development of the young are described here for the first time. Breeding biology was studied in 1989 at a nest in south Sumatra, Indonesia. The nest was in the transition zone between mangrove and freshwater swamp forest. Incubation took less than 29 days, and two eggs hatched. Fish 2–7 cm long comprised 67% of the prey for feeding young. The chick was fully feathered at 52–57 days and was seen flying when 57–62 days old. The species is rare in south Sumatra. It occurs in low numbers and flocks of up to seven birds were observed. The density is estimated at 20–40 birds within 110,000 ha of primary swamp forest. At this density, the population would be below 100 birds in south Sumatra and between 100 and 300 in Indonesia. The species is threatened by development and conversion of primary swamp forest.     

Habitat variation and population regulation in Sparrowhawks

In a study area in south Scotland, Sparrowhawks did not occupy the available nesting places at random, but more often used those places where breeding success was highest (here called high-grade places). Most birds stayed on particular nesting places for only one year, but others stayed up to 8 years. Some birds moved from low- to high-grade places as they aged. Continued occupancy of certain places was thus produced by many different individuals occupying such places in rapid succession, but most staying for only one breeding season.
On the most used (high-grade) nesting places pairs produced more than enough young per breeding attempt to offset the average annual mortality, but on the less used (low-grade) places they produced too few. Low-grade nesting places therefore acted as a sink, whose occupancy could be maintained only by continual immigration. Over the study area as a whole, the population was in balance, with reproduction matching mortality.
Habitat changed over periods of 15–30 years, as woodland matured. Nesting places in young woods, with small densely-growing trees, showed the highest occupancy and nest success. Both aspects of performance declined as the woodland aged, and trees became larger and more widely spaced. Long-term stability in nest numbers and success in the study area as a whole was associated with a system of rotational forest management, which ensured a continuing availability of young woods.
It is proposed that spatial variation in habitat quality is involved in the regulation of breeding numbers. Removal experiments confirmed the presence of non-breeders, which could attempt to breed when high-grade nesting habitat was made available to them, but otherwise remained as non-breeders despite the presence of vacant low-grade habitat. This situation, involving an interaction between habitat quality and bird quality, probably occurs in some other raptors too.     

BREEDING PERFORMANCE OF PUFFINS FRATERCULA ARCTICA IN RELATION TO NEST DENSITY, LAYING DATE AND YEAR

The paper presents data on the breeding and predation of Puffins in two areas of different nest density within a single colony on Dun, St Kilda group, Outer Hebrides in 1973-78.
Within a season birds laying early had a slightly higher nesting success than birds laying late, but laying date had little influence on the peak and fledging weights of young. The main disadvantage in late laying was a reduced chance of relaying if the first egg was lost.
Breeding success and chick weights varied from year to year. The 1974 season was the least successful with the lowest nesting success, lowest frequency of feeds, lowest calorific value of feeds, lightest chicks and slowest growth. Overall breeding performance was not related to the annual mean laying dates.
In all years pairs nesting in the area of high nest density did better than pairs nesting at low density. The effect is attributed to differential predation and disturbance by predatory gulls. At least 4.2% of adult Puffins breeding in the area of low burrow density were killed by gulls each breeding season; this is higher than the total annual mortality found in three other studies. Only 0.9% of adults from the high density area were found killed. The subpopulation in the low density area cannot survive without much immigration, yet there is no evidence that this happens.     

Colonization and population growth of Yellow-legged Gull Larus cachinnans in southeastern Poland: causes and influence on native species

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 Yellow-legged Gull in Poland, located in a sedimentation basin near Tarnów (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 Tarnów 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.     

Effects of supplementary food on density-reduced breeding in an African eagle: adaptive restraint or ecological constraint?

Increased population density often reduces reproductive output in breeding birds, but the underlying mechanisms (adaptive restraint v reduced food resources) behind decreased productivity are poorly understood. Here I correlatively and experimentally investigated the roles of food, breeding density, latitude, altitude and rainfall in limiting productivity of Wahlberg's Eagles Aquila wahlbergi throughout Africa. Breeding success in equatorial and subtropical Africa (0°–30°S) was highly density-dependent but showed no latitudinal or rainfall-related trends. Pairs in dense populations produced half as many young annually as pairs in low-density populations. Density (but not rainfall or latitude) also explained much of the geographic variation in the mean proportion of pairs attempting to breed each year and the incidence of two-egg clutches.
Breeding within populations was consistent with these density-dependent trends: incidence of two-egg clutches increased in a declining population, and productivity was inversely related to breeding density and rainfall combined. To determine if reduced food resources accounted for reduced output in dense populations, eight pairs were food supplemented: supplementary food failed to induce nonbreeding pairs to breed: nor did it induce earlier laying or increase egg size or clutch-size. Population density itself was unrelated to two correlates of food resources, rainfall and latitude. I conclude that population density influences most aspects of breeding in Wahlberg's Eagles, and reduced food resources do not appear to explain these trends. Hence, adaptive restraint may account for decreased annual reproduction in this species.     

Population dynamics of the bearded vulture Gypaetus barbatus in southern Africa

The essential features of mortality and survivorship of bearded vultures Gypaetus barbatus in southern Africa were deduced from age class plumage characteristics. The population consisted of about 204 adult pairs within a breeding range of about 35,000 sq km. Pairs bred every year and produced, on average, about 0·9 young per pair per year. Young birds made up about 37% of the population, subadults 3·5% and adults 60%. About 182 fledged young were recruited to the population each year. The proportion of young birds in the population in different areas was inversely related to the breeding density of adult birds (range 24–47%). Young bird mortality over the four years to subadult age was 87%, the survival rate of adults was 94% and the mean lifespan of birds surviving to adulthood was 21·4 years. This study demonstrates the need to understand the relationship between adult breeding density and young bird numbers in different parts of their range to accurately deduce population dynamics characteristics.     

Long‐term breeding demography and density dependence in an increasing population of Golden Eagles Aquila chrysaetos

Few studies have quantified the dynamics of recovering populations of large raptors using long‐term, spatially explicit studies. Using data collected over 37 years in the western Italian Alps, we assessed the trends in distribution, abundance, fecundity and breeding population structure of Golden Eagles Aquila chrysaetos. Using the spatial distribution of territory centroids in 2007, we found that the spatial distribution of eagle territories was over‐dispersed up to 3 km. Although population size and total productivity increased from 1972 to 2008, the proportion of pairs that laid eggs showed a strong decline, falling to no more than 50% after 2003. On average, 15% of successful nests produced two fledglings, and productivity also declined over time. No significant relationship between population growth rate and total population size was detected, but the percentage of pairs that bred and breeding success showed evidence of density dependence, as they declined significantly with increasing density. Our results suggest that density dependence, operating across heterogeneous habitats, is currently regulating this population, while the carrying capacity may still be increasing. This may explain the apparent paradox of reduced breeding effort despite increasing total productivity.     

Population-specific adjustment of the annual cycle in a super-swift trans-Saharan migrant

For migratory birds optimal timing of the onset of reproduction is vital, especially when suitable conditions for reproduction occur only for a short while during the year. With increasing latitude the suitable period becomes shorter and we expect the organization of annual cycle to be more synchronized to the local conditions across individuals of same population. This should result in low variation of arrival and departure date in breeding sites at higher latitudes. We quantify the temporal and geographical variation in pre- and post-breeding migration between individuals from four different populations of alpine swifts Tachymarptis melba along a latitudinal gradient. We tracked 215 individuals in three years with geolocators. The two western and two eastern populations showed separate migratory flyways and places of residence in Africa. Length of stay at the breeding sites was negatively correlated with latitude and differed by more than a month between populations. Duration of migration was similarly short in all populations (median 6.2 days in autumn and 8.7 days in spring). However, variation in timing of migration was unrelated to latitude and individuals everywhere arrived in the same asynchrony at the breeding site.     

Status and structure of the griffon vulture (Gyps fulvus) population in Crete

Griffon vulture (Gyps fulvus) population surveys were conducted during 1996–2002 in the island of Crete (Greece) to document population status and structure. Fieldwork was carried out during the breeding period when birds could be monitored in their colonies. Total population size was estimated at 379 individuals (range = 341–417) with adult birds comprising 63%. The breeding population was estimated at 141 pairs, which were distributed on an average in 23 colonies per year (range = 16–30) while the mean number of breeding pairs that laid eggs was 98 (range= 64–126). Crete thus supports the largest insular population of the species in the world and hosts 70–80% of the breeding population of the species in Greece. Population density was estimated at 6.9 individuals/100 km², 2.6 breeding pairs/100 km² and 1.8 nesting pairs/100 km². The average home range of an occupied colony (i.e., breeding group) was estimated at ca. 204 km² producing a theoretical foraging range of 8 km radius around the breeding cliff. No trends in the total number of individuals and breeding pairs appeared to exist, although significant differences in population size of individual colonies occurred between the years. The majority of the population was concentrated in small-sized colonies, which showed a low occupancy rate. The number of abandoned sites and the colonization of new ones could represent a shift of breeding pairs to alternative colonies provoked by local food abundance and conspesific attraction.     

Estimation and limitation of numbers of floaters in a Eurasian Sparrowhawk population

Over a 20‐year period, the numbers of Eurasian Sparrowhawk Accipiter nisus nests found in a 200 km² area in south Scotland remained relatively stable (mean 33.3 pairs, CV = 10.6%). Nest numbers fluctuated from year to year in a manner expected of a population subject to density‐dependent regulation. The numbers of non‐breeders (floaters) could not be counted directly, but the number of female floaters was estimated, using known mortality rates, from the numbers of females recruited to the breeding population each year at different ages. Female floater numbers were estimated by two methods: Method A assumed that birds bred for the first time in their first, second or third year, in the same ratio as they were found breeding for the first time in the study area; and Method B assumed that all third‐year birds found breeding for the first time in the study area had bred previously, unknown to us, outside the area. Under Method A, floaters consisted of some 1‐year and some 2‐year birds; while under Method B, floaters consisted only of some 1‐year birds. Under both methods, the estimated number of female floaters fluctuated greatly from year to year, but under Method A they averaged 0.90 per female breeder, and under Method B they averaged 0.28 per female breeder. The Method B estimate was most consistent with other data and with the finding that some birds found breeding in the study area were likely to have bred previously outside the area (because of territory changes). Moreover, the mean and variance in female floater numbers estimated by Method B were similar in magnitude to the values obtained in a simulation model. In this model, breeding density was given a fixed ceiling, while breeding success was allowed to vary from year to year within the limits observed in the study area. It was concluded that (a) recruitment of floaters to the breeding sector was density dependent with respect to breeder numbers, i.e. broadly speaking, floaters filled gaps in the territorial system left by the deaths and movements of established breeders; and (b) floater numbers themselves were probably not regulated in a density dependent manner, but depended on whatever was the balance between annual additions (from reproduction and immigration) and subtractions (from mortality, emigration and entry to the breeding sector).     

The breeding biology and causes of nest failure of Scottish Black-throated Divers Gavia arctica

The breeding biology and causes of nest failure were examined for Black-throated Divers Gavia arctica in core areas of their Scottish breeding range in 1983–1987. Breeding was confirmed for up to 88% of territorial pairs each year ( n = 28–62), and 76% of nests were on islands. Hatching success was consistently low with, on average, only 43% of territorial pairs managing to hatch a clutch each year; 64% of recorded nest failures occurred during the first week of the 4-week incubation period.
Overall breeding success in West Sutherland in 1984–1987 averaged 0.23 chicks per territorial pair per year, while in Ross-shire for 1986–1987 it was 0.29. Forty percent of hatched chicks survived to fledge, and 92% of recorded deaths occurred in the first fortnight after hatching; 4.8% of fledged broods held two chicks.
Causes of nest failure were assessed with the aid of surveillance cameras. Approximately 30% of losses were due to water level changes (mostly floods), 48% to predators (primarily nocturnal mammals, but also Hooded Crows Corvus corone ), 13% to human egg collectors and 5% to desertion following human disturbance.
Scottish Black-throated Divers produce only half the number of chicks tentatively estimated to be required to maintain a stable population. The main difference between the Scottish and more successful Swedish populations is in the degree of chick mortality.