A method to assess population changes in king penguins: the use of a Geographical Information System to estimate area-population relationships

During the last decades, king penguin (Aptenodytes patagonicus) populations have been reported to increase throughout most of their breeding range. In this study, we compared the results obtained from direct counts of incubating king penguins with the results yielded by the estimation of the change in area occupied by breeding birds at the Ratmanoff king penguin colony at the Kerguelen Islands. The area of the colony was determined using a Geographical Information System with a georeferencing extension on aerial pictures taken in 1963, 1985 and 1998. Individual king penguin were counted on the same pictures or pictures taken on the same day. The overall population increase between 1963 and 1998 was 733% while the colony area increased by 677%. This study indicates that monitoring change in colony size is a good indicator for detecting and monitoring large population changes in king penguins, in particular for remote colonies. The discrepancy between the two results may be from two different kinds of bias. Firstly, there could be a possible error in the estimation of the area occupied by the colony resulting from the georeferencing of oblique pictures, and secondly, the density of king penguins may also change with population number. This method, which only requires high-altitude pictures, also reduces the possible disturbance to breeding made by low- to medium-altitude flights. Accepted: 7 February 2000     

Riding the tide: intriguing observations of gulls resting at sea during breeding

Adult Lesser Black‐backed Gulls Larus fuscus were followed during the breeding season using a high‐resolution GPS tracking system. Little is known about the foraging movements of these birds and what they do when they are away from the colony. The study revealed intriguing yet infrequent behavioural patterns showing that birds would sit on the sea surface drifting passively with the tidal current for several hours, resting at sea rather than in the breeding colony. The potential function of the observed patterns is discussed as well as the relevance of these observations to other species.     

Growth and decline of a penguin colony and the influence on nesting density and reproductive success

Colonial breeding is characteristic of seabirds but nesting at high density has both advantages and disadvantages and may reduce survival and fecundity. African penguins (Spheniscus demersus) initiated breeding at Robben Island, South Africa in 1983. The breeding population on the island increased in the late 1990s and early 2000s before decreasing rapidly until 2010. Before the number breeding peaked, local nest density in the areas where the colony was initiated plateaued, suggesting that preferred nests sites were mostly occupied, and the area used by breeding birds expanded. However, it did not contract again as the population decreased, so that nesting density varied substantially. Breeding success was related positively to the prey available to the breeding birds and negatively to local nest density, particularly during the chick-rearing period, suggesting a density-dependence operating through social interactions in the colony, possibly exacerbated by poor prey availability when the breeding population was large. Although nest density at Robben Island was not high, nesting burrows, which probably reduce the incidence of aggressive encounters in the colony, are scarce and our results suggest that habitat alteration has modified the strength of density-dependent relationships for African penguins. Gaining a better understanding of how density dependence affects fecundity and population growth rates in colonial breeders is important for informing conservation management of the African penguin and other threatened taxa.     

An emperor penguin population estimate: the first global, synoptic survey of a species from space

Our aim was to estimate the population of emperor penguins (Aptenodytes fosteri) using a single synoptic survey. We examined the whole continental coastline of Antarctica using a combination of medium resolution and Very High Resolution (VHR) satellite imagery to identify emperor penguin colony locations. Where colonies were identified, VHR imagery was obtained in the 2009 breeding season. The remotely-sensed images were then analysed using a supervised classification method to separate penguins from snow, shadow and guano. Actual counts of penguins from eleven ground truthing sites were used to convert these classified areas into numbers of penguins using a robust regression algorithm.We found four new colonies and confirmed the location of three previously suspected sites giving a total number of emperor penguin breeding colonies of 46. We estimated the breeding population of emperor penguins at each colony during 2009 and provide a population estimate of ~238,000 breeding pairs (compared with the last previously published count of 135,000-175,000 pairs). Based on published values of the relationship between breeders and non-breeders, this translates to a total population of ~595,000 adult birds.There is a growing consensus in the literature that global and regional emperor penguin populations will be affected by changing climate, a driver thought to be critical to their future survival. However, a complete understanding is severely limited by the lack of detailed knowledge about much of their ecology, and importantly a poor understanding of their total breeding population. To address the second of these issues, our work now provides a comprehensive estimate of the total breeding population that can be used in future population models and will provide a baseline for long-term research.     

The incidence of the parasitic disease trichomoniasis and its treatment in reintroduced and wild Pink Pigeons Columba mayeri

The recovery programme for the endangered Pink Pigeon Columba mayeri Prévost, 1843 of Mauritius has involved intensive management to promote rapid population growth. As the Pink Pigeon population has increased in size and distribution, disease problems have emerged that have affected wild and reintroduced birds. Trichomoniasis first appeared in the remnant wild population in 1992, and became established in a reintroduced subpopulation on the offshore island of Ile aux Aigrettes. We aimed to control the disease by treating individuals and, on Ile aux Aigrettes, by routinely treating the population with medicated drinking water. On Ile aux Aigrettes, 49% of squabs were clinically diseased and only 27% of all squabs survived without treatment. Treatment of squabs that were not clinically diseased improved survival from 36 to 82%, suggesting that subclinical infections also affected survival. Subclinical infections were demonstrated by microscopy in 22% of Pink Pigeons and 17% of exotic doves on Ile aux Aigrettes. Clinical disease was observed in 4.5% of adults and 3.1% of juveniles, but more juveniles than adults died from the disease. It is likely that Trichomoniasis and other diseases will continue to affect the Pink Pigeon's recovery and the species may require long-term management to counteract the effects of disease and other limiting factors.     

Confirmation of a wintering ground of Ross's Gull Rhodostethia rosea in the northern Labrador Sea

Ross's Gull Rhodostethia rosea is one of the world's least known seabirds; < 1% of the estimated global population can be accounted for at known breeding sites, and its wintering range has never been determined. Anecdotal reports over the last two centuries have prompted extensive speculation as to possible wintering areas used by this species in the north Pacific/Bering Sea region, but none has ever been confirmed. Using satellite and geolocator telemetry, we show that some Ross's Gulls from a colony in the Canadian Arctic winter in a restricted area of the northern Labrador Sea. Our discovery of a wintering area in the northwest Atlantic indicates that Ross's Gulls breeding in the Nearctic may be part of a disjunct population, or that birds breeding in the Palaearctic may winter off the east coast of North America.     

Movements of radio-tagged Grey Herons Ardea cinerea during the breeding season in a large pond area

This paper describes the strategies of resource utilization in the course of the breeding season by five radio-tagged Grey Herons Ardea cinerea. The seasonal changes in exploitation of the environment by two breeding adults, one non-breeding adult and two non-breeding first-year birds were studied from March to August 1982, near Zonhoven in Belgium. Two adult breeding birds could be followed continuously from the end of March until the middle of June. During the first month they explored an extended area all around the colony, but each concentrated its search in a specific direction. From the end of April until the beginning of June, most probably from egg-hatching until the end of breeding activities, each bird spent a very large proportion of its time at a particular feeding site, from which other herons were actively excluded. In the first part of June they again visited different sites, each maintaining its preferred direction. From the middle of June onwards they seemed to have left the fish-pond area. The pattern of movements of the first-year birds differed markedly from that of the breeding adults. In April, although both non-breeding and breeding birds explored large areas, only the areas used by non-breeders were centred on the colony. From the end of April onwards, probably after general egg-hatching in the colony, the non-breeders very rarely revisited the colony, and from May till August their ranges became more and more restricted to very small areas at an increasing distance from the colony. They were never observed defending particular sites. The results are discussed with regard to recent speculations about the evolution of colonies as an adaptation for the exploitation of food resources. Breeding herons seem to explore a large part of the environment during incubation and defend a particular site while feeding their young. Choice of feeding site by non-breeding birds may be influenced by the site defence of the breeding birds. Non-breeding birds exploit a large area when breeding birds occupy feeding territories. Perhaps they are forced to forage in less suitable places at this time. Colonies might have evolved as a strategy to minimize effort in resource esploitation as, especially at the beginning of the breeding season, the colony could act as an assembly point in the exploration of the environment. However, its importance as an assembly point diminishes in the course of the season, as non-breeding birds no longer visit the colony and adults defend territories.     

Effects of vegetation on nest microclimate and breeding performance of lesser black-backed gulls (Larus fuscus)

For birds that breed in large colonies, the overall area occupied by the colony generally comprises several sub-areas that differ in physical and social features such as vegetation and breeding density. Birds arriving at a breeding colony select their nesting sites through a hierarchical process of selecting a sub-area, then a particular nest site with appropriate biotic and physical attributes. Optimal vegetation cover is one such important attribute. Many ground nesting gulls preferentially select nest sites that provide shelter during reproduction, but this presumably has to be balanced against any costs such as reduced visibility of potential predators. The effects of vegetation height in the sub-areas within a colony, and of the amount of vegetation in the immediate vicinity of the nest on nest microclimate were investigated in lesser black-backed gulls Larus fuscus in a colony in which overall vegetation height differed in different sub-areas and was patchily distributed within these areas. Tall vegetation did have a sheltering effect, and this was positively related with chick growth. However, this vegetation area was associated with lower breeding densities, relatively late laying birds and lower chick survival rate, suggesting that sub-areas with tall vegetation held more lower-quality or young breeders. Within the sub-areas, the birds preferentially selected nest sites with more surrounding vegetation, and this was positively correlated with their hatching success.     

Using super‐high resolution satellite imagery to census threatened albatrosses

This study is the first to utilize 30‐cm resolution imagery from the WorldView‐3 (WV‐3) satellite to count wildlife directly. We test the accuracy of the satellite method for directly counting individuals at a well‐studied colony of Wandering Albatross Diomedea exulans at South Georgia, and then apply it to the closely related Northern Royal Albatross Diomedea sanfordi, which is near‐endemic to the Chatham Islands and of unknown recent population status due to the remoteness and limited accessibility of the colonies. At South Georgia, satellite‐based counts were comparable to ground‐based counts of Wandering Albatross nests, with a slight over‐estimation due to the presence of non‐breeding birds. In the Chatham Islands, satellite‐based counts of Northern Royal Albatross in the 2015/2016 season were similar to ground‐based counts undertaken on the Forty‐Fours islands in 2009/2010, but much lower than ground‐based counts undertaken on The Sisters islands in 2009/2010, which is of major conservation concern for this endangered albatross species. We conclude that the ground‐breaking resolution of the newly available WV‐3 satellite will provide a step change in our ability to count albatrosses and other large birds directly from space without disturbance, at potentially lower cost and with minimal logistical effort.     

Reedbed selection and colony size of breeding Purple Herons Ardea purpurea in southern France

Reedbeds of Phragmites australis have declined in Europe in recent decades. Moreover, in some European countries the remaining reedbeds are intensively managed for industrial reed cutting, hunting or grazing. Several species of conservation concern, such as herons and pelicans, use reedbeds as their principal breeding habitat. At the same time, data on habitat use and colony size of these species in relation to reedbed management practices are scarce. We investigated habitat characteristics of 71 reedbeds occupied or unoccupied by breeding Purple Herons Ardea purpurea in the Rhône delta (Camargue) and in other Mediterranean coastal marshes in southern France. In addition, data on colony size in occupied reedbeds were collected from aerial surveys. Reedbeds occupied by breeding Purple Herons were unharvested, or only partially harvested, in winter and had higher water levels in spring compared with unoccupied reedbeds. A logistic regression model with reed harvesting intensity and water levels in mid‐April as independent variables correctly classified reedbed use for 94.7% of the reedbeds in the study. A model with water levels in mid‐April alone was only 90.9% accurate, suggesting that low water level in spring is the most important factor limiting reedbed occupation by breeding Purple Herons. A general linear model indicated significant effects of harvesting intensity and reedbed surface area on colony size. Within occupied reedbeds there was a strong tendency for colony size to increase with increasing reedbed surface area. Given the recent developments in reed harvesting and wetland management in southern France and elsewhere in Europe, these results provide the first information on potential effects of these practices on reed nesting herons, and suggest that Purple Heron conservation is likely to be favoured by maintaining large uncut reedbeds with relatively high water levels in spring. The possible effect of changes in habitat on the Purple Heron population in southern France is discussed.     

Colony specific variation in the use of a moulting site in the migratory little tern Sterna albifrons

Individual-based data on little terns Sterna albifrons at a post-breeding moulting area were used to investigate the spatial extent at which this site attract birds. Combining information collected on young terns, ringed at the natal colonies, with that on birds captured a few months later at the moulting site, we estimated a survival/movement parameter for each age-by-colony combination. This parameter is the product between the survival probability and the probability to visit the moulting site. The distance between the natal colony and the moulting site negatively influenced the probability of reaching the site in yearlings. Having corrected for the distance from the moulting area, colony characteristics explained only about 10% of the spatial variation in the survival/movement parameter of juveniles. In older birds that had visited the site at least once in their life, neither the colony nor the distance affected the survival/movement parameter significantly. The average annual adult survival/movement probability was 0.90. Juvenile survival between June and September was 0.60. Overall results suggest that the moulting area could act as a 'population funnel' within a system of moult migration that involves birds breeding up to 500 km away. However, other unknown moulting site must exist within this area that could be important for the conservation of the species.     

Life cycle of the tick Ixodes uriae in penguin colonies: relationships with host breeding activity.

A survey of the temporal pattern of population structure and feeding activity of the seabird tick Ixodes uriae was conducted for the first time in two host species colonies: King penguin (Aptenodytes patagonicus halli) and Macaroni penguin (Eudyptes chrysolophus chrysolophus). The life cycle of the tick was investigated over 3 years in a King penguin colony and 2 years in a Macaroni penguin colony at Possession Island (Crozet Archipelago). There was a marked seasonal feeding activity pattern of ticks in both host species, connected with the presence of birds during the breeding season. Although the King penguin colonies were occupied throughout the year by birds, the favourable period for engorgement was limited to 3.5-4.5 months, and almost all the ticks overwintered in the unengorged state. Consequently, I. uriae probably completed its life cycle over 3 years in King penguin colonies. In contrast, this life cycle could be shortened to 2 years in Macaroni penguin colonies, as a result of a different timetable of the presence of birds for breeding and moulting. The relationships between such plasticity and the host behaviour and subantarctic climatic conditions are discussed.     

Timing of migration and residence areas during the non‐breeding period of barn swallows Hirundo rustica in relation to sex and population

We investigated sex‐ and year‐dependent variation in the temporal and spatial movement pattern of barn swallows Hirundo rustica during the non‐breeding period. Hundred and three individuals equipped with miniaturized light‐level geolocators at three different breeding areas in southern Switzerland and northern Italy provided data for the analysis. We identified a region 1000 km in radius centred in Cameroon as the main non‐breeding residence area of these three geographical populations. Five residence areas of males only were in southern Africa, south of 19°S. Most individuals occupied a single site during their stay south of the Sahara. The timing of migration broadly overlapped between sexes and all geographical breeding populations. Between the two study years there was a distinct difference of 5 to 10 d in departure dates from and arrival at the breeding sites. Remarkably, the period of residence in sub‐Saharan Africa was very similar (157 d) in the two study years, but their positions in the first year (2010–2011) were about 400 km more to the north than in the second (2011–2012). Independent of the year, individuals with sub‐Saharan residence areas further north and east had a shorter pre‐breeding migration and arrived earlier than those staying further south and west. In addition, birds breeding in southern Switzerland arrived at their breeding colony 7–10 d later than those breeding only 100 km south, in the Po river plain. Our study provides new information on the variance in migration phenology and the distribution of residence areas in sub‐Saharan Africa in relation to sex, population and year. It supports the usefulness of light‐level geolocators for the study of annual routines of large samples of small birds.     

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.     

Movements of Eiders Somateria mollissima on the east coast of Britain

Movement patterns, sex differences in natal dispersal and breeding dispersal, and interchange of birds between colonies were studied in the population of Eiders Somateria mollissima breeding on the east coast of Britain. First-winter Eiders reared at the Sands of Forvie, Grampian, remain at or close to the colony, while most adults move about 100 km south to winter on the Firths of Forth and Tay. A proportion of the Forvie population is sedentary. Eiders which breed in Northumberland either move north to winter on the Tay and Forth estuaries or remain close to their breeding areas. Eiders breeding in Fife are sedentary. Recoveries of British-ringed Eiders in Scandinavia indicate that some British-born males join the Baltic breeding population, probably by pairing with Scandinavian females wintering in Britain. There is extensive natal dispersal of males from Forvie, with more than twice as many Forvie-bred females as males returning to the colony to breed. The breeding dispersal of males is also twice that of females. Dispersal of males from the relatively sedentary Forvie wintering population is less than that from the breeding population. Previous work suggested that at Forvie sedentary birds nesting close to the estuary were genetically isolated from migratory ones nesting along the coast. This situation is less clear cut than had been supposed previously, with many migrants nesting close to the estuary. It is unlikely that the genetic differences between females nesting in different parts of the Forvie colony will remain stable in the long term, due to the natal and breeding dispersal of males.     

Age and breeding success related to nest position in a White stork Ciconia ciconia colony

Coloniality is a breeding system that may produce benefits in terms of breeding success, although these advantages could vary according to factors such as colony size or nest position. We studied breeder's age in relation to nest position (peripheral or central) within the colony. In addition, we studied the relationship between breeding success and nest position, controlling for breeder's age, a highly correlated factor, in a White Stork Ciconia ciconia colony over a 7-year period. Our results show that central nests are mainly occupied by adult birds and had lower failure rates. However, controlling for breeder's age, nest position per se did not explain breeding success. The scarce predation and the lack of human disturbance in the study colony could explain the absence of differences in breeding success between different nest positions within the colony.     

Winter Fidelity and Apparent Survival of Lesser Snow Goose Populations in the Pacific Flyway

Abstract The Beringia region of the Arctic contains 2 colonies of lesser snow geese (Chen caerulescens caerulescens) breeding on Wrangel Island, Russia, and Banks Island, Canada, and wintering in North America. The Wrangel Island population is composed of 2 subpopulations from a sympatric breeding colony but separate wintering areas, whereas the Banks Island population shares a sympatric wintering area in California, USA, with one of the Wrangel Island subpopulations. The Wrangel Island colony represents the last major snow goose population in Russia and has fluctuated considerably since 1970, whereas the Banks Island population has more than doubled. The reasons for these changes are unclear, but hypotheses include independent population demographics (survival and recruitment) and immigration and emigration among breeding or wintering populations. These demographic and movement patterns have important ecological and management implications for understanding goose population structure, harvest of admixed populations, and gene flow among populations with separate breeding or wintering areas. From 1993 to 1996, we neckbanded molting birds at their breeding colonies and resighted birds on the wintering grounds. We used multistate mark-recapture models to evaluate apparent survival rates, resighting rates, winter fidelity, and potential exchange among these populations. We also compared the utility of face stain in Wrangel Island breeding geese as a predictor of their wintering area. Our results showed similar apparent survival rates between subpopulations of Wrangel Island snow geese and lower apparent survival, but higher emigration, for the Banks Island birds. Males had lower apparent survival than females, most likely due to differences in neckband loss. Transition between wintering areas was low (<3%), with equal movement between northern and southern wintering areas for Wrangel Island birds and little evidence of exchange between the Banks and northern Wrangel Island populations. Face staining was an unreliable indicator of wintering area. Our findings suggest that northern and southern Wrangel Island subpopulations should be considered a metapopulation in better understanding and managing Pacific Flyway lesser snow geese. Yet the absence of a strong population connection between Banks Island and Wrangel Island geese suggests that these breeding colonies can be managed as separate but overlapping populations. Additionally, winter population fidelity may be more important in lesser snow geese than in other species, and both breeding and wintering areas are important components of population management for sympatric wintering populations.     

TERRITORY ESTABLISHMENT AND STABILITY IN McCORMICK'S SKUA

This paper describes the way in which a new pair of McCormick's Skua became established in a vacant area in a breeding colony. The pair worked out from a central point to meet neighbouring birds on the original boundaries so that these became re-established. Within three days of settling most of the vacant area was claimed and the pair was behaving as a recognised member of the breeding group. Eggs were laid in the first season.
Following comparison with other species it is proposed that the stability found in territory boundaries from year to year arises because territories becoming vacant are occupied by replacement pairs while neighbours are inhibited from encroaching on them.     

Migration and winter distribution of Iberian and central European black storks Ciconia nigra moving to Africa across the Strait of Gibraltar: a comparative study

This paper compares the migratory movements of Iberian and central European satellite‐tagged black storks Ciconia nigra moving to Africa across the Strait of Gibraltar. Results show that the populations differ in departure dates from breeding areas (central European birds start to move 15 d before Iberian birds), cross the Strait of Gibraltar together and reach the Sahel on similar dates. This synchronic arrival to the Sahel may be related with the onset of suitable conditions for the species after summer rains, when many pools are available for fishing. In this area, Iberian birds occupied westernmost localities compared to central European birds crossing the Strait of Gibraltar, which were distributed closer to those storks arriving in Africa across the Bosporus. This suggests that the parallel distribution of breeding and wintering areas results from posterior rearrangements of the two populations crossing Gibraltar. These patterns appear to be linked to the increasing population of central European black storks located on the western side of the migratory divide that moves throughout the western flyway to sectors of the Sahel close to their ancestral wintering grounds.     

Is food availability limiting African Penguins Spheniscus demersus at Boulders? A comparison of foraging effort at mainland and island colonies

The African Penguin Spheniscus demersus (Vulnerable) formed three new colonies during the 1980s, two on the South African mainland (Stony Point and Boulders) and one on Robben Island. One of the mainland colonies, at Boulders, Simon's Town, is in a suburban area, resulting in conflict with humans. Growth of the Boulders colony was initially rapid, largely through immigration, but has since slowed, possibly as a result of density‐dependent effects either on land (where there has been active management to limit the spread of the colony) or at sea. We test the latter hypothesis by comparing the foraging effort of Penguins feeding small chicks at island and mainland sites, and relate this to the foraging area available to birds. Three‐dimensional foraging paths of African Penguins were reconstructed using GPS and time–depth loggers. There were no intercolony differences in the rate at which birds dived during the day (33 dives/h), in diving depths (mean 17 m, max. 69 m) or in travelling speeds. The maximum speed recorded was 2.85 m/s, with birds travelling faster when commuting (average 1.18 m/s) than when foraging (0.93 m/s) or resting at sea (0.66 m/s during the day, 0.41 m/s at night). There were strong correlations between foraging trip duration, foraging range and total distance travelled. Foraging effort was correlated with chick age at Robben Island, but not at Boulders. Contrary to Ashmole's hypothesis, birds from Boulders (c. 1000 pairs) travelled further (46–53 km) and foraged for longer (13.2 h) than did birds from Robben Island (c. 7000 pairs) and Dassen Island (c. 21 000 pairs) (33 km, 10.3 h). The mean foraging range also differed significantly between mainland (18–20 km) and island colonies (9 km). The area available to central‐place‐foraging seabirds breeding on the mainland is typically less than that for seabirds breeding on islands, but the greater foraging range of Boulders birds results in an absolute foraging area roughly twice that of island colonies, and the area per pair is an order of magnitude greater for the relatively small Boulders colony. Ashmole's hypothesis assumes relatively uniform prey availability among colonies, but our results suggest this does not apply in this case. The greater foraging effort of Boulders birds probably reflects reduced prey availability in False Bay, and thus the recent slowing in growth at the colony may be the result of differential immigration rather than management actions to limit the spatial growth of the colony.