Tern Numbers Research Articles

Höststräcket av fisktärna Sterna hirundo och silvertärna S. paradisaea över södra Sverige

Simultaneous observations of migrating Common and Arctic Terns were carried out during afternoons and evenings for three years, 1990—1992, at eleven sites at the larger lakes in southern Sweden. The force and direction of wind seemed to be the most important factor determining the number of terns observed and the route they took when they passed mainland Sweden from the Baltic Sea. The principal direction of the migration was southwest, with a more westerly orientation for Arctic than for Common Tern. High numbers were recorded mainly in head winds, whereas the terns probably flew at high altitude in tail winds, when they were not observed from the ground. The orientation of the lakes in relation the migration direction also affected the counts by leading line effects. The terns often concentrated in the southern or southwestern parts of the lakes before they continued migration. Approximately 65,000—70,000 Common and Arctic Terns are estimated to pass the region in the autumn.

Variable Success in Breeding of the Roseate TernSterna dougalliion the Northern Great Barrier Reef

Breeding of Roseate Terns Sterna dougallii on the northern Great Barrier Reef (11°-15°S) was monitored between 1976 and 1994, and they were recorded breeding on the inshore rocky islands in most years, usually starting April-May. Between 50-5000 pairs were recorded breeding each year and indicate that the northern Great Barrier Reef is an important breeding area for Roseate Terns during peak years when large colonies of 1000-5000 pairs formed on low sand cays in the far northern Great Barrier Reef (11°s). On at least three occasions, breeding success was poor in these large colonies, with high mortality of the almost-fledged chicks. Growth in weight and wing length of Roseate Tern chicks was measured at Eagle Island (14°42′S) between 1983 and 1986 in order to assess the influence of food on growth rates and survival. Chicks took up to 35 days to fledge, significantly longer than the ecologically similar, more numerous Black-naped Tern Sterna sumatrana at the same site at the same time and also almost 10 days longer than Roseate Tern chicks from temperate North American colonies. These data suggest that conditions in northern Australia are rarely favourable for the rapid growth and breeding success of Roseate Terns. Pelagic fish populations around inshore islands in tropical Australia may only be able to support limited numbers of Roseate Terns during the breeding season. This makes northeastern Australian populations of this globally threatened species extremely vulnerable to changes in the availability of their prey during the breeding season.

Responses by four seabird species to a fluctuating availability of Cape Anchovy Engraulis capensis off South Africa

In recent years, Cape Anchovy Engraulis capensis has been the most important food for four seabirds breeding in South Africa–African Penguin Spheniscus demersus, Cape Gannet Morus capensis, Cape Cormorant Phalacrocorax capensis and Swift Tern Sterna bergii. Between 1984 and 1992, biomass of spawning anchovy fluctuated between about 0.5 and 1.75 million tons. Abundance of anchovy was significantly related to numbers of chicks fledged by African Penguins, occurrence of anchovy in the diet of Cape Gannets and numbers of Cape Cormorants and Swift Terns that attempted to breed. Numbers of African Penguins and Cape Gannets that attempted breeding probably also were influenced by abundance of anchovy. African Penguins and Cape Cormorants abandoned nests when anchovy were scarce and deferred breeding until anchovy became more plentiful. Survival of immature African Penguins in a period of anchovy scarcity was enhanced by availability of South African Sardine Sardinops sagax as an alternative food. When anchovy abundance was low, Cape Gannets fed on sardine.

Least Tern and Piping Plover Nesting at Sand Pits in Nebraska

-Endangered Least Terns (Sterna antillarum) and threatened Piping Plovers (Charadrius melodus) nest at commercial sand and gravel mining operations (sand pits) along the Platte River system in Nebraska. Sandbar habitat has been disappearing since the early 1900's along the Platte River system, but numbers of sand pits have increased. We hypothesized that birds would more fully utilize sand pits where suitable sandbar habitat was limited. We inventoried sand pits and censused terns and plovers on both habitats along the Loup River, part of the North Loup River, and most of the Platte River during 1988-1991. Using aircraft, we also quantified features of suitable sand pits present on the central Platte in 1988 and lower Platte in 1990, and related features to abundance and presence of birds. We found 225 sand pits of which 78 were suitable and 187 were unsuitable for nesting. Along the central Platte, where sandbar habitat is severely degraded, birds nested at 81% of the suitable sand pits (N = 32) at least once during 1988-1991, and most birds (61-94%) nested on sand pits. Along the lower Platte, where both sandbar and sand pit habitat are plentiful, birds nested at 60% of the suitable sand pits (N = 35) at least once during 1988-1991, and most birds (60-86%) nested on sandbars. Numbers of terns and plovers were more weakly correlated with features of sand pits on the central Platte than on the lower Platte. Least Terns and Piping Plovers seem to use more of the suitable sand pit habitat on the central Platte than on the lower Platte. Sand pits probably have influenced the birds' distribution by providing alternative nesting habitat along rivers where suitable sandbars are rare or absent. Received 4 February 1993; accepted 7 July 1993.

Population Changes, Breeding Cycles and Breeding Success over Six Years in a Seabird Colony at Michaelmas Cay, Queensland

Seabirds were counted on Michaelmas Cay every month from May 1984 to April 1990. Seven species bred during the study. The major breeding species were Sooty Tern Sterna fuscata, Common Noddy Anous stolidus, Crested Tern S. bergii and Lesser Crested Tern S. bengalensis. Silver Gull Larus novaehollandiae, Black-naped Tern S. sumatrana and Bridled Tern S. anathaetus bred in some years in small numbers. Sooty Terns had a sub-annual breeding cycle of 8.6 months duration, measured between peaks of breeding numbers, while the other species were annual breeders, five in summer and one (Silver Gull) in winter. In successive breeding cycles, the sizes of breeding populations of Sooty Tern and Common Noddy both fluctuated strongly. Crested Tern numbers increased slightly then decreased, and Lesser Crested Tern numbers increased strongly then decreased again. Average Silver Gull numbers remained fairly stable over the study period. Fledging success varied considerably among breeding cycles of Sooty Tern, Common Noddy and Crested Tern. Lesser Crested Terns bred successfully in three cycles and showed increasing fledging success over the study period. Climate had a major influence on breeding populations of Sooty Tern and Common Noddy. Three cyclones were recorded; one altered the periodicity of Sooty Tern breeding cycles and two affected its breeding numbers and success. In mid-year, prolonged periods of strong winds caused breeding failures in Sooty Tern and Common Noddy. Erosion of the cay also caused nest losses. Human disturbance had little effect on breeding populations.

Population trends in bird species at Dungeness, Kent

HILL, D. & MAKEPEACE, P., 1989. Population trends in bird species at Dungeness, Kent. This paper investigates trends in a number of bird species at Dungeness in Kent incorporating the Royal Society for the Protection of Birds (RSPB) reserve, in order to quantify the effects of management on bird communities. Dungeness is a site of national geomorphological importance. Past conservation management at the site has focussed on re-establishing the seabird colony and on increasing habitat for terns, common gull and breeding wildfowl species by island creation and vegetation control (for terns). Data are presented for wintering wildfowl, wintering and passage waders, breeding wildfowl, gulls, terns and selected passerines, together with species richness during both winter and breeding periods. SUMMARY Most wintering wildfowl species increased in numbers on the Dungeness Reserve during the period 1969-87, particularly teal, gadwall and wigeon. Wigeon, teal and gadwall showed the fastest rates of increase. An exponential model provided a better fit to the data for smew and gadwall than a linear one. Populations were more or less as variable in number in the early years of management (1969-77) as in subsequent years (1978-86). Of wintering and passage wader species, turnstone, redshank, black-tailed godwit and common sandpiper increased. Snipe showed a decline in abundance in spring. Numbers of black terns, the only non-wading migrant analysed, remained variable over the period. Breeding tufted duck and great-crested grebe increased in numbers during the period 1969-86 whereas mallard declined. Black-headed gull numbers increased, as did exponentially-breeding common and sandwich terns. Of four passerine species analysed, only breeding reed warblers increased during the period 1968-86, whereas numbers of breeding sedge warbler and whitethroat remained stable. Wheatear numbers declined in early years but have increased since 1983. Increases in species richness were documented in wintering and passage, and breeding species.

The breeding seabirds of the Firth of Forth, Scotland

SynopsisThe seabird colonies in the Firth of Forth are spectacular. Although the total numbers of individual birds of most species are relatively small, the populations of gannet, herring and lesser black-backed gulls, sandwich, roseate, little and common terns make up more than 10% of the Scottish total. Numbers of fulmar, shag, cormorant, great black-backed gull, kittiwake, guillemot, razorbill and puffin have all increased, the rates varying from 4% per annum (kittiwake) to 20% p.a. (puffin). The numbers of cormorants stabilised soon after the species colonised the Forth in 1957. The period of rapid increase in guillemot numbers may now be over. Numbers of little terns have probably increased, but roseate and common terns have both declined and the number of sandwich terns is more-or-less stable. Herring and lesser black-backed gulls both increased dramatically up to 1972, since when breeding birds have been culled. The herring gull then decreased significantly, but the situation is less clear in the lesser black-backed gull. We set these changes in a wider context and discuss some possible reasons for the observed population trends.

Common Tern Foraging: Seasonal Trends in Prey Fish Densities and Competition with Bluefish

We present a method for making direct quantitative measurements of population dymamics of fish species preyed upon by seabirds. We studied foraging behavior of Common Terns (Sterna hirundo) in relation to density of fish prey of Long Island, New York. We used an echo sounder to record the abundance of small prey fish and large predatory fish near a tern colony. Prey fish abundance was highest when terns were feeding young chicks and declined sharply later in the season, coincident with the arrival of large numbers of predatory bluefish (Pomatomus saltarix). Mean depth of occurrence of prey fish was shallower after the arrival of bluefish. Terns fished in areas with high concentrations of prey, but there was no correlation between numbers of feeding terns and prey density. Number of feeding terns was inversely correlated with prey depth, however. Terns were strongly attracted to predatory fishes feeding near the surface. We suggest that in addition to concentrating prey fish near the surface, predatory fish may have been important as competitors.

Distribution and Numbers of Large Terns in Northwestern Venezuela during 26 January-5 February 1983

Distribution and Numbers of Large Terns in Northwestern Venezuela during 26 January-5 February 1983

Paralytic Shellfish Poisoning: Effects on Breeding Terns

--More than 70 Common Terns (Sterna hirundo) and lesser numbers of other terns and gulls were killed on 11-12 June 1978, by Paralytic Shellfish Poisoning (PSP; toxin of the dinoflagellate Gonyaulax excavata) at a breeding colony in Massachusetts. PSP toxin was detected at lethal levels in sand-launce (Ammodytes americanus), the terns' principal food. Almost all terns that died were females in pre-laying condition; other birds vomited and survived. Breeding performance of survivors was unaffected. Mortality was greatest in three-year-old birds; 10-25% of three-year-old females were killed. Although PSP toxin was present in local shellfish for about three weeks, tern mortality was limited to a few hours on two days. Much higher levels of toxin were detected in shellfish at other parts of the Massachusetts coast in 1978 and other years, but terns and other susceptible seabirds were unaffected. Paralytic Shellfish Poisoning (PSP) results from ingestion of a toxin produced by marine algae and which accumulates primarily in molluscs. In the North Atlantic, the organism primarily responsible for producing the toxin is a dinoflagellate (Gonyaulax excavata, formerly known as G. tamarensis), whose periodic blooms are known as red tides (Loeblich and Loeblich 1975, Sweeney 1976, White 1980a). The toxin acts by blocking propagation of nerve impulses, leading to paralysis of skeletal muscles and, in sufficient doses, to death from respiratory failure (Schantz 1973). It has recently been discovered that the toxin can accumulate in marine zooplankton to levels that are lethal to planktivorous fish (White 1977, 1980b, 1981 a, b). However, there are few reports of PSP in piscivorous fish or piscivorous birds. McKernan and Scheffer (1942) reported mortality of Common Murres (Uria aalge) and loons (Gavia spp.) in an outbreak off Washington state. Coulson et al. (1968) and Armstrong et al. (1978) reported two incidents in northeastern England, in which large numbers of breeding Shags (Phalacrocorax aristotelis), Great Cormorants (P. carbo) and Northern Fulmars (Fulmarus glacialis) and smaller numbers of Herring Gulls (Larus argentatus) and terns (Sterna spp.) were killed. Effects on the terns in the 1968 incident were described in more detail by Horobin (1970) and Dunn (1972). In this paper I describe a similar incident at a tern colony in Massachusetts, in which I was able to document differential effects upon ageand sex-classes.

Distribution and Numbers of Common Terns on the Lower Great Lakes during 1900-1980: A Review

Distribution and Numbers of Common Terns on the Lower Great Lakes during 1900-1980: A Review

The breeding of the Sooty tern Sterna fuscata in the Seychelles and the effects of experimental removal of its eggs

In the Seychelles the eggs of the Sooty tern Sterna fuscata are collected for human consumption. A reduction in the number of Sooty terns breeding in exploited colonies has been attributed to over‐exploitation of the eggs. However, the population decline has been over‐estimated and factors other than exploitation have led to a reduction in the land area available to breeding colonies.In the study colony, on Bird Island, egg laying was highly synchronous, and birds which laid at peak laying time had a higher reproductive success than those that laid early or late. The higher success of these birds was due to their being at the same stage of the reproductive cycle as their neighbours: this reduced losses of eggs to predators and losses of chicks due to pecking by adults and other chicks. Birds which laid late, which included young birds and birds which had lost their first egg and laid a replacement, were therefore penalized.The ability to lay a replacement egg after loss of the first, was found experimentally to be much greater than previous estimates had suggested, and some individuals were induced to lay a third egg. Both the ability to relay and the success of replacement eggs declined seasonally. The laying of a replacement egg did not seem to place extra strain on the parents, and the lower weights of most replacements compared with first eggs was due to seasonal factors rather than to the inability of adults to produce a large second egg.The food brought by the parents to the chicks consisted mainly of fish and squid, but frequent and abrupt changes in the species composition of the food suggested that food supplies were unpredictable. In 1973 chick growth was interrupted by two periods of food shortage, and although late hatched chicks experienced this food shortage early in their lives, starvation did not appear to be a major source of mortality.The regulation currently in force in the Seychelles imposing a close season for egg collecting protects only late‐laid eggs, and since these have a very low success rate and can contribute little to future generations, there is no biological foundation for continuing this restriction. Adult mortality and age at first breeding are not known for Seychelles Sooty tern populations, and exploitation should be restricted to 10–20% of the birds that lay during the main laying period.

The Numbers of Terns and Shearwaters Nesting on Heron is. in 1965

The Numbers of Terns and Shearwaters Nesting on Heron is. in 1965

NOTES ON AUTUMN MIGRATION AT THE BOSPHORUS AND IN THE AEGEAN

Summary1. Migration was studied at the Bosphorus from 20 August to 8 September 1959 and observations made at the Dardanelles, on Lesbos, and in parts of Greece.2. Daily counts of soaring birds migrating over the Bosphorus are given. The species involved were principally White Storks Ciconia ciconia, Honey Buzzards Pernis apivorus, and Black Kites Milvus migrans. Few eagles Aquila sp. were seen.3. The winds were mostly strong, northeasterly. Heavy migration occurred only when the wind was light. It is considered that migration of soaring birds over the Bosphorus is virtually inhibited by strong N.E. winds; but whether they cross the Sea of Marmara to the south is undecided.4. White Storks were observed migrating over the Sea of Marmara and the pattern of their migration through the area is discussed.5. Both nocturnal and diurnal migrant passerines were recorded in only moderate numbers.6. Large numbers of gulls and terns (Laridae), especially of Little Gulls Larus minutus, were seen in the Bosphorus and elsewhere.

The War and Nesting Birds

THE most interesting effect of the War upon nesting birds in Great Britain has been the attraction of the black redstart (Phcenicurus ochrurus gibral-tariensis) to nest in the air-raid ruins of some English towns. Until the War, this was one of the rarest British nesters, although a regular winter visitor, but on the Continent where it is a familiar town bird it shows a partiality for ruins and it would be interesting if it becomes a commoner British resident in this unexpected way. In 1923 this bird was first noted nesting in Great Britain in a southern county and in 1936 it began nesting in Cambridge.. In 1940 and 1941 it nested in the city area of London and a considerable number of London Natural History Society observers watched the birds. Another influence upon nesting birds has been the military disturbance of many coastal and rural haunts, the felling of woods and the draining of marshland. Another rare British nester, the black-necked grebe (Podiceps nigricollis nigricollis), was under observation by the Merseyside Naturalists' Association this year at a new nesting site at Abbot's Moss, the third it has used in Cheshire. In Anglesey there was a considerable increase in the number of roseate terns nesting at Llandwyn island, where between sixty and seventy pairs nested this year with Sandwich terns, etc., and new terneries, possibly an overflow of this species, were made at Malldraeth Point and on Ynys Ferrig rocks in Rhosneigr Bay. The kite has, however, maintained its nesting haunt in the valleys of mid-Wales and the black guillemot its recent habitat on the Cumberland cliffs at St. Bees Head.

History of a Nesting Colony of Caspian Terns on San Francisco Bay

It was in 1924 that information was first brought to Mlr. Chase Littlejohn, veteran naturalist of Redwood City, that a colony of Caspian Terns (Hydroprogqne caspia imperator) was breeding somewhere in the southern reaches of San Francisco Bay. The man who brought Mr. Littlejohn the information stated that a few of the birds had been noted in 1922 and again in 1923, but it was not until 1924 that they became numerous. He was asked to bring in a few of the eggs the next time he came to town, which he did the following week. These eggs, together with a vivid description of the birds, convinced Mr. Littlejohn and myself that Caspian Terns were breeding in the Bay district. It was not until July 4, 1926, however, that we were able to affirm positively our earlier convictions, by making a trip to the nesting colony. Leaving Redwood City by automobile about five-thirty on the morning of the fourth it did not take us long to reach a group of salt ponds on the southeastern side of the Bay, where the colony had previously been located. These ponds were enclosed and subdivided by a series of dikes or levees and it was upon one of the latter that the birds had been reported nesting. The question was, which one of the many miles of dikes had the birds selected: not an easy problem, as the dikes all looked exactly alike. With the aid of a field glass we eventually picked up a rather steady flight of birds all of which seemed to be headed toward a single point on one of the dikes, some half-mile distant. Upon closer scrutiny of this particular area we were quite sure that we could see a closely massed colony of nesting birds. Eagerly anticipating the pleasure of stepping into the center of a breeding colony of this species we put on full steam ahead. As we approached our destination we could clearly see an ever increasing number of terns flying to their breeding grounds. Several of them came quite close to us, making it possible to identify them as Caspian Terns. Each one seemed to be heavily laden with fish, which evidently it was carrying home to a hungry family. When we were still a hundred yards from the colony all of the adults sailed into the air emitting a rather startling, if not terrifying, chorus of tern blasphemy. The more daring members came right out to meet us, some of them actually swooping down to within a few inches of our heads. Each time one darted at us it let out