Total Breeding Population Research Articles

Population size and trends within the two populations of Southern Buller's Albatross Diomedea bulleri bulleri

The abundance and distribution of Southern Buller's Albatross ( Diomedea bulleri bulleri) were investigated at the Solander Islands in February 1996 and at The Snares in March 1997. The total breeding population of this endemic subspecies was estimated at 11 502 breeding pairs. At the Solander Islands, a total of 2625 occupied nests was estimated from aerial and ground counts in the first accurate census that included all islands in the group. Comparisons with the number of chicks counted on Little Solander Island in 1985 indicated a possible decrease of 18.7% or no change in the numbers of breeding pairs during the period 1985–1996. At The Snares, a total of 8242 occupied nests was counted and a further 635 were estimated on North East Island, Broughton Island, and associated islets and stacks. A comparison with the numbers of occupied nests counted on North East Island, The Snares, during 1969 and 1992 indicated population increases of 78% and 8% during the periods 1969–1992 and 1992–1997, respectively. Differences in the rates of change within The Snares population demonstrate the complexity of population parameters within a single seabird species, thus emphasising the need for careful formulation of conservation measures.

Ammonium in coastal Antarctic aerosol and snow: Role of polar ocean and penguin emissions

Year‐round aerosol samples collected in the boundary layer at coastal Antarctic sites (Dumont D'Urville, Neumayer, and Halley) indicate a seasonal cycle of ammonium concentrations with a minimum in winter (April–September). A large intersite difference appears in the summer (November–February) maxima values, from ∼12.5 ng m−3 at Neumayer to 140–230 ng m−3 at Dumont D'Urville. At Dumont D'Urville, ammonium concentrations are the largest ever reported from Antarctic sites, and the large summer maxima are associated with large enrichments with respect to sea salt for potassium and calcium. In addition, seasonal ammonium variations at Dumont D'Urville are in phase with a well‐marked seasonal cycle of oxalate concentrations which exhibit maxima of 5–10 ng m−3 in spring and summer and minima of less than 0.5 ng m−3 in winter. Such a composition of aerosols present in the boundary layer at Dumont D'Urville in summer is linked to the presence of a large Adélie penguin population from the end of October to March at the site. Ornithogenic soils (defined as guano‐enriched soils), together with the bacterial decomposition of uric acid, are a source of ammonium, oxalate, and cation (such as potassium and calcium) aerosol, in addition to a subsequent large ammonia loss from ornithogenic soils to the atmosphere. The total breeding population of 5 million Adélie penguins widely distributed around the Antarctic continent may emit, at most, some 2.5 × 10−4 Mt of NH3‐N during the summer months. In contrast, Halley and Neumayer Stations are far less exposed to penguin colony emissions. At Neumayer, ammonium concentrations peak from January to March and are in phase with the increase of biogenic sulfur species. Here the NH4+/(MSA + nss SO4−) molar ratio is close to 13% in summer aerosol and to 40% in winter aerosol. Using this summer ratio, which may be related to ammonia and sulfur oceanic emissions occurring south of 50°S in summer and estimated DMS emissions in these regions at this time, we derive an upper limit of 0.064 Mt NH3‐N emitted per year by the high‐latitude Southern Ocean in summer. This study indicates a very limited ammonia neutralization of acidic sulfate aerosols at high southern latitudes, except in the vicinity of ornithogenic soils occupied by large penguin colonies.

Newly discovered breeding sites of Olrog's GullLarus atlanticusin Argentina

SummaryOlrog's GullLarus atlanticusis a threatened and endemic species to the Argentine Atlantic coast. We present information on seven new colonies and update information on known colonies obtained during 1992–1995. Five of the new colonies were in southern Buenos Aires and two in southern Chubut. Total population size, including already known colonies, was estimated at 2,300 breeding pairs. All colonies were located on islands and islets and were associated with breeding Kelp GullsLarus dominicanus.The new colonies extend the known breeding range of Olrog's Gull to the north and increase the overall known population size. However, the aerial survey also showed that two colonies found in 1990 no longer exist. Almost 40% of the total breeding population breed within the Bahía Blanca estuary, an area currently subject to intense human pressure. Olrog's Gull is still a species with restricted distribution and low population size. We suggest conservation actions needed to adequately protect this threatened species.

The breeding distribution and status of Abbott's booby (Sulidae: Papasula abbotti) on Christmas Island, Indian Ocean

The breeding distribution and population status of the endangered seabird Abbott's booby (Sulidae: Papasula abbotti (Ridgway) Olson & Warheit, 1988) were assessed by an island-wide survey on Christmas Island (Indian Ocean) in 1991. The species is now endemic to the island. A total of 1833 breeding sites were located, and it is estimated that the total breeding population is around 2500 pairs, 600 pairs more than the most recent estimate of 1900 pairs in 1983. We do not interpret the difference as a genuine increase in the breeding population — instead, we attribute it to the discovery of areas on the island where Abbott's boobies have probably always nested, but have never been recorded. Although this result has alleviated immediate concern for the future of P. abbotti, fields cleared for phosphate mining prior to 1987 still pose a continuing threat to the species — 36% of the population still nest near enough to clearings to be adversely affected by them. The Australian Nature Conservation Agency is currently rehabilitating mined fields to reduce their impact on the breeding population, and to eventually create a new breeding habitat for P. abbotti.

The abundance of breeding KnotCalidris canutus islandica

Six sites around Borup Fiord, west central Ellesmere Island, Canada, were surveyed for breeding Knot Calidris canutus islandica. Breeding density at the main study site was estimated using a calculation based on hatching success, brood counts and the probability of broods being resighted: estimates from other sites were based on this assessment. Density at the main study site was 4.6 pairs/km2, varying between 0.4 and 12.7 pairs/km2 in different areas. Density was negatively correlated with spring snow cover. At other sites density estimates ranged from nil to 5.7 pairs/km2. Brood counts and registrations of territorial activity accounted for only 33% and 67% of pairs, respectively. A literature review suggested that within the Knot's breeding range, densities appear to be highest in areas showing a warm regional climate, early snow-melt, and high vegetational diversity and density. The Knot's dependence on such areas may be related to its size and need for an early start to breeding. The total breeding population of C.c.islandica was estimated to be 61 000 pairs, or 304 000 individuals in autumn. Over-optimistic estimates of breeding numbers and productivity, however, may mean that about half of the Knots wintering in Europe may not be C.c.islandica.

Distribution and numbers of breeding ivory gulls Pagophila eburnea in Severnaja Zemlja, Russian Arctic

The ivory gullPagophila eburnea has a semi-circumpolar distribution with breeding sites in the High Arctic. Data about ivory gulls in the Severnaja Zemlja Archipelago (Siberia) were collected from 1991 to 1995. The numbers of breeding ivory gulls and their egg-laying period arc correlated with the sea ice situation and weather during the first part of the summer. We estimate that the total potential breeding population of Severnaja Zemlja is about 2000 pairs, which makes up approximately 20% of the Russian and 14% of the world ivory gull breeding population. The percentage of the total breeding population which actually breeds varies annually. The most important breeding area of the ivory gull in Severnaja Zemlja is the Sedov Archipelago (A. Sedova) where a large colony (from 410 to about 1100 pairs in different years) was found on flat ground on Domašmj Island. Colonies from 10 to 100 breeding pairs, mostly on steep cliff faces, occur on O. Oktjabr'skoj Revoljucii and O. Bo?ševik. The ivory gull is included in the Red Data Book of Russia. Parts of Severnaja Zemlja. with important breeding sites, have become a nature reserve.

Assessing the population size of the European storm petrel () using spatial autocorrelation between counts from segments of criss-cross ship transects

Van der Meer, J., and Leopold, M. F. 1995. Assessing the population size of the European storm petrel (Hydrobates pelagicus) using spatial autocorrelation between counts from segments of criss-cross ship transects. ‐ ICES J. mar. Sci., 52: 809‐818. European storm petrels were counted on criss-cross ship transects on the continental shelf between Ireland and Spain. No element of randomisation was involved in the selection of the sampled area. A geostatistical model which explicitly considers the spatial autocorrelation between observations from transect segments, was therefore used to predict population size in the study area. The model also provides standard errors of the prediction. Although some of the underlying assumptions of the model were questionable, several alternative approaches yielded almost similar predictions, suggesting model robustness. The prediction of the total number of European storm petrels present in the study area is equivalent to 255 000 breeding pairs. This is much higher than previous estimates of the total breeding population of the region, ranging from 50 000 to 100 000 pairs. ? 1995 International Council for the Exploration of the Sea

Satellite remote sensing in monitoring change of seabirds: use of Spot Image in king penguin population increase at Ile aux Cochons, Crozet Archipelago

The king penguin colony at Ile aux Cochons, Crozet Archipelago (southern Indian Ocean) is the largest in the world. The change in its surface area was investigated by means of satellite remote sensing using spot scene. The satellite picture enabled us to locate the colony and to determine that the surface area occupied by the colony has increased by 56% between 1962 and 1988. The increase in the surface area occupied by the colony was confirmed by a map realised in 1982 (by the Institut Geographique National). The high resolution system available on the spot system which allows at present at 10 m ground resolution, and 5 m in the near future, can thus be a useful tool for monitoring medium to long-term changes in marine bird populations breeding in colonies composed of birds spaced a constant distance from one another. Based on the surface area occupied by the colony and the published data on the population size on Possession Island, as well as information on the breeding frequency of the species, we estimated that the total breeding population is about 1,000,000 pairs for the whole archipelago and that about 70% of birds breed at Ile aux Cochons.

Factors Affecting the Distribution and Size of Pygoscelid Penguin Colonies in the Antarctic

Using census data on three species of pygoscelid penguins, we tested the hypothesis that competition for food during the chick-provisioning stage of reproduction limits the number of conspecific seabirds in a region. This prey-depletion hypothesis predicts that a negative correlation should exist between colony population size and the total number of breeding pairs from other colonies within parental foraging range. We also tested whether or not a negative correlation exists between colony size and the population size of, or distance to, the nearest neighboring colony. Suitable data were available for Adélie, Chinstrap, and Gentoo penguins (Pygoscelis adeliae, P. antarctica, P. papua) along the coasts of Victoria Land and the Antarctic Peninsula, where major portions of these species' world populations nest. Results indicated that colonies were highly clustered, with small colonies grouped around one or two large ones, in turn spaced widely. Depending on species, two different patterns of geographic structuring were observed. For the Adélie and Gentoo penguins, no significant negative correlation existed between colony size and the total number of pairs breeding within parental foraging range of the reference colony; however, a significant negative correlation occurred at 150 and 200 km, well beyond foraging range. We found no relationship between colony size and size of or distance to the nearest neighboring colony. In contrast, for the Chinstrap Penguin, a significant positive correlation existed between colony size and total breeding population within the foraging range (50 km) but, as with the other two species, the correlations became more negative at greater distances. Moreover, a significant positive correlation existed between colony size and size of, but not distance to, the nearest colony in this species. We confirmed the hypothesis previously put forward that prey depletion by parents feeding chicks cannot explain size structuring of seabird colonies where breeding-season food supply is superabundant, as in polar regions. However, we also showed that prey depletion is not a necessary condition for negative size structuring. We suggest that if prey depletion occurs (by exploitative or interference competition), any manifestation in terms of colony distribution is overridden near to the colony by aggregating factors that originally led penguins to be colonial and philopatric, for example, social facilitation or predator avoidance. We further propose that geographic structuring is better explained by factors affecting the metapopulation (all breeders and nonbreeders associated with the colony cluster), especially during the prebreeding period, than by factors affecting chick-provisioning parents alone.

Impacts of human visitors on breeding success and long-term population trends in Ad�lie Penguins at Casey, Antarctica

Breeding populations of Aelie Penguins Pygoscelis adeliae have been counted at two localities near Casey Station in Wilkes Land, East Antarctica since 1959/60 and 1968/69. At Whitney Point, the breeding population increased from 1122 pairs in 14 colonies in 1959/60 to 4714 pairs in 36 colonies in 1992/93. All new colonies at Whitney Point established on relict colony sites identified in 1959/60. On Shirley Island, the total breeding population has remained at 7770 pairs ±10% between 1968/69 and 1992/93, except in 1990/91 when the population peaked at 8719 pairs. An association between the age of a colony and its rate of increase was observed at Whitney Point, with new colonies (those established since 1971/72) increasing more rapidly than colonies extant in 1959/60. At Shirley Island, where most of the colonies extant in 1968/69 have decreased in population, the establishment and growth of 13 colonies has offset this decrease; these new colonies also exhibited the association between age and rate of increase. Breeding success (chicks fledged per nest) was significantly lower for Shirley Island colonies than for those at Whitney Point. Human visitors to Shirley Island from Casey station are believed to be responsible for the observed changes in the distribution and abundance of breeding pairs and for maintaining the stable population by reducing overall breeding success through the disturbance associated with visits.

Estimation of the breeding population of the Sooty Tern Sterna fuscata on Nakanokami-shima, South Ryukyu, Japan

During our surveys on Nakanokami-shima from 1975 to 1984, seven species of sea birds were recorded breeding. Among them, the Sooty Tern Sterna fuscata was probably the most abundant. Fig. 1 shows the locations of colonies of the species in 1981, 1982, and 1983. The photographs were taken from selected high points situated west and east of the main colony. Based on these photographs, the number of the birds which stayed on the colony in the daytime was counted; while the birds on subcolonies were counted through binocular. The results of counting are shown in Table 1.Attendant birds on early stage of breeding season were adult plumaged. Most of these birds remaining during the daytime seemed to be occupying nest sites, and it seemed that one bird of each pair stayed on the nest site while other bird was absent offshore. If the number of non-breeding birds, including immatures, was negligible, then the number of birds staying on the colonies in the daytime should be equivalent to the number of breeding pairs. On the above presumption, the breeding population of the main colony were c. 6000 pairs in 1981, c. 3500 pairs in 1982, and c. 2500 pairs in 1983. This remarkable annual variation is due to the fact that the centre of the main 1981 colony was covered with tall dead herbage in early 1982; and with well grown grass in 1983 (Fig. 2). The changes in the vegetation resulted in fewer pairs settling in the area. On the other hand, neither the apparent increasing of breeding density as a whole nor the expansion of colony did occure in 1982, and in 1983.In 1982, the number of fledgling in the main colony on 22 August was c. 1800; approximately 0.51 chicks per pair. However on 9 August, 1982, a strong storm (Typhoon-8211) had passed the island and 300 dead chicks were found in the main colony on 18 August. Therefore, the production of chicks per pair just before the accident was probably at least 0.60.The estimations of total breeding population in 1981, 1982, and 1983 were 6400 pairs, 4100 pairs, and 3000 pairs respectively.

Distribution, abundance and conservation of the bald ibis Geronticus calvus in Southern Africa

Updated information is provided on the breeding distribution and abundance of the bald ibis Geronticus calvus in southern Africa. Results of long-term, comprehensive surveys of the species in the Transvaal and Orange Free State are presented, and combined with information on the bird's breeding abundance in Natal to estimate its total breeding population in South Africa. The bald ibis's status in Swaziland and Lesotho is also examined. The South African breeding population is estimated at approximately 3440 birds, while its total breeding population may exceed 4600 birds. Human disturbances at its breeding sites, and degradation of its grassland biotope, pose the greatest threats to the bald ibis. Recommendations for improving the conservation of the species are discussed.

Distribution, population size and conservation of the jackass penguinSpheniscus demersus

The jackass penguin, endemic to southern Africa, is the only member of the Sphenisciformes now breeding in Africa. Its breeding distribution extends from Sylvia Hill, South West Africa (Namibia), to Bird Island, Algoa Bay, South Africa. The non-breeding range extends from Sette Cama, Gabon, to Inhaca Island, Moçambique. Jackass penguins do not usually occur far off shore. The minimum total breeding population in 1978/79 was estimated to be approximately 134 000 birds. Numbers halved between 1956 and 1978 alone as a result of collapses in the South and South West African pilchard populations. Numerical decreases at Possession and Dassen Islands were particularly severe. Prior to 1956 numbers had also decreased, primarily because of large collections of eggs. Sealing activities and guano harvests may also have influenced trends. Only colonies at the periphery of the breeding distribution have increased numerically in recent times, and such increases appear to be related to the availability of suitable prey. Although the species breeds in captivity and is unlikely to become extinct, its continued survival in the wild probably relies on the continued good state of the pelagic fish resources.

The decline of the Thick-billed Murre in Greeland

The total breeding population of the Thick-billed Murre (Brünnich's Guillemot)Uria lomvia in west Greenland in 1951 was estimated to amount to two million pairs (Salomonsen, 1951), half of which inhabit the gigantic loomery at Kap Shackleton (Agparssuit) (Fig 1). Tuck (1960) considered this to be a conservative estimate, ‘and cannot concede that fewer than five million Thick-billed Murres inhabit the west coast of Greenland during the summer months’. The birds have long been considered an important food source by the inhabitants of the area. Rink (in Salomonsen, 1951, p 378) recorded a harvest of 70 000 birds as long ago as 1850; with the advent of modern shotguns and cheap ammunition the toll is now severe (Fig 2). As a result of shooting and disturbance population decreases have been recorded at various sites, but particularly those close to settlements (Table 1). In addition to the colonies listed in the table, a count was made in 1921 for the Sagdleq colony in the Umánaq district. An estimated 500 000 birds were recorded which, in 1949, had decreased to 250 000. In 1968 the Umánaq district legislated for total preservation of this colony for three years.

The status of the Bald Ibis of Southern Africa

The Bald Ibis ( Geronticus calvus) is an uncommon bird that is peculiar to the Southern African region where it is restricted to the highlands and more mountainous districts of the southeastern part of the subcontinent. The bird's numbers and distributional range have contracted during historical times. Although the species is in no immediate danger of extinction, man-made influences have been responsible for the extermination of local populations. The species' distribution is reported, as well as the results of surveys undertaken to determine the numerical strength of the breeding population. The total breeding population is estimated at 2,000 birds. Little is known about the biology of the Bald Ibis, and further study is needed as a basis for future monitoring of the bird's status and conservation. Consideration should be given to proclaiming and managing one or two selected breeding-sites as Bald Ibis reserves.

Distribution and size of colonies of white pelicans, Pelecanus erythrorhynchos, in Canada

On the basis of a count of 14 103 nests, the total breeding population of white pelicans in Canada was estimated to consist of 30 000 birds for the years 1967–1969, seven times higher than previous estimates. The boundaries of the Canadian breeding range of pelicans were found to coincide closely with the 0 °C isotherm in April, the southern boundary of the Canadian Shield, and the eastern boundary of the Rocky Mountains. As those factors appeared to be closely related to the availability of fish, it is concluded that the extent of the breeding range of the pelicans in Canada is mainly determined by the food supply. Besides availability of fish, pelicans appeared to require nesting sites inaccessible to mammalian predators.

Natalité et mortalité dans une population naturelle d’un passereau tropical, le Lagonosticta senegala

The breeding cycle, clutch size and frequency, mortality rate of eggs, nestlings and adults, and general productivity of a wild population of the Senegal fire-finch Lagonosticta senegala, banded at the Ornithological Station of Richard-Toll, Sénégal, were studied during the period 1954 to 1964. The breeding season lasts for 9 months, from the first half of July to the beginning of April. During the season a single individual adult male has been shown by banding to be capable of breeding four times in succession. Despite the fact that they have been hatched in different months of the breeding season, the young all reach maturity simultaneously, about the beginning of August, and are then ready to breed in their turn. Both the number of eggs and the number of fledglings produced per pair of breeding adults each year are very high, off-setting the high mortality rate of the population. Only 45 % of the eggs laid are hatched, and only 28 % of them result in fledged young. The adult death rate has been estimated in two different ways ; by the use of the «composite life table», as defined by Hickey, in the case of males, and by calculating the percentage of banded individuals breeding for the first time out of the total breeding population. Both methods give an average annual adult mortality rate of 70 to 75 %. Despite the fact that a very small percentage of individuals in the population survived to an old age (7 years), the expectation of life of the newly-hatched Senegal Fire-finch is low and the population turnover rapid. At the nest stage the parasitic weaver Hypochera chalybeata is one of the most important mortality factors among nestlings. Although clutch-size is the same in normal and parasitized nests (3.5 and 3.3), and although the percentage of eggs hatching is the same in both cases, the mortality among nestlings is twice as high (53 %) in parasitized nests as in normal nests (25 %).

THE BIOLOGICAL SIGNIFICANCE OF THE TERRITORIES OF BIRDS.

Summary.This paper forms an introduction to a symposium on the territorial behaviour of birds.Following Noble (1939), territory is defined as “any defended area”. A simple classification of breeding territories is given, and the diversity of territorial behaviour emphasized.Territorial behaviour can be analysed into at least two components—restriction of some or all types of behaviour to a particular area, and defence of that area. These are often accompanied by self‐advertisement.The aggressive behaviour which arises in different situations depends primarily on the same mechanisms, though the fighting may be specialized to serve different functions (e.g. to defend different objects). This justifies the broad definition of territory given above.The fighting involved in territorial defence is associated with tendencies both to attack and to flee from the rival.The nature of the evidence concerning the biological functions of territorial behaviour is considered. In previous discussions of this subject the term “function” has sometimes been used to refer to any advantageous consequence of the behaviour, and sometimes restricted to consequences through which selection in favour of the behaviour can act.Various possible functions of territory are considered.Circumstantial evidence suggests that the familiarity with the area which results from site attachment may assist feeding, escape from predators, etc., and may also increase fighting potentiality.There is strong evidence that territorial behaviour, in addition to producing over‐dispersion, can regulate density in favoured habitats. There is no direct evidence that territory limits the total breeding population in all habitats.In many species, it facilitates the formation and maintenance of the pair‐bond.It may also reduce interference in various reproductive activities by other members of the species.Defence of the nest‐site is an important consequence of territorial behaviour in many species, and the aggressive behaviour is often clearly specialized to this end.In a few species territory is primarily concerned with food, but in most the food value of the territory is not significant. Even in the species which feed on their territories, the territorial behaviour is not specialized for the defence of food objects:in these cases it is possible, but unproven, that the territorial behaviour does help to ensure an adequate supply of food for the young.In some species the over‐dispersion produced by territorial behaviour may reduce predation, though direct evidence that this is the case is not available.Maintenance of a territory may reduce the despotism of other males, but this does not explain the function of territorial aggressiveness.Territorial behaviour may reduce disease, but this is unlikely to be a significant consequence except in some colonial species.It is unlikely that the prevention of inbreeding and the promotion of range extension are significant consequences of territorial behaviour.The functions of territorial behaviour are extremely diverse, and the quality of the evidence available for assessing them is little different from that available to Howard. Since territorial behaviour has consequences both harmful and advantageous to the individual's chances of ultimate reproductive success, and since the inter relations between the selective forces governing behaviour, structure and physiology are extremely complex, simple answers about the function of territory cannot be expected.

A Census of Breeding Gannets (Sula bassana) on Myggenaes Holm, Faeroes

THE earliest reference to the gannet (Sula bassana L.) in the Faeroes occurs in the medieval Faeroese ballad Fuglakvaebi (5), where it is mentioned with a number of other birds, most of which are still common in the islands. This source does not record any breeding place, and at the present time gannets only nest on the holm which lies to the west of the island of Myggenaes, and on the neighbouring stacks, Pikarsdrangur and Flatidrangur. The early works of Debes (3), Svabo (12), and Landt (8) record the position of the colony, but unfortunately do not give any indication of the number of breeding pairs. Landt (1800), probably following Svabo, gives the number of adults killed in April as 200; and the same number of young birds was caught in September. Muller (9), writing 62 years later, says that the number of adults and young taken annually was 300 and 600 respectively. Feilden (4) visited Myggenaes in 1872, but was unable to cross to the Holm, and Barrington (2) in 1892 estimated the Myggenaes Gannets at 1500 , i.e. 750 pairs. Hagerup (7) gives photographs but no estimate. Wynne-Edwards, Lockley & Salmon (1936) (16) base their figure of 750 breeding pairs on an estimate by Miss Acland (1) in 1928, and on the observations of Lockley, who passed close to the colony in June 1935, and estimated that not more than 1000 birds were present. Salomonsen (10) gives no estimate of the total breeding population, but records the number of birds caught annually in recent years as about 450 adults and 850 young. During a visit to Myggenaes in July 1937, the present writers were told by some of the bird-catchers themselves that they only take 600-800 young from the Holm and the two stacks together, of which 150 are caught on Flatidrangur. No adult birds are taken at the present time. The lack of agreement in these various observations made it desirable to re-examine the status of the Myggenaes colony.