Royal Terns Research Articles

Competition for Nest Sites between Kelp Gulls (Larus dominicanus) and Terns (Sterna maxima and S. eurygnatha) in Patagonia

Seabirds frequently nest in mixed-species colonies (Burger 1985). Several studies have shown differences in habitat and nest-site use among seabirds (Buckley and Buckley 1980, Croxall and Prince 1980, Fasola and Canova 1992). However, some degree of overlap in habitat and nest-site requirements may exist between species, resulting in interspecific competition that often leads to nest-site displacement or even the replacement of one species by another (Buckley and Buckley 1980, Burger 1985). Spatial interactions between seabirds can be more intense in areas where habitat is limited or when the population of one of the species is expanding (Burger and Shisler 1978, Trivelpiece and Volkman 1979, Duffy 1983, Ainley 1990). At many mixed colonies of larids, larger species often displace smaller species from their territories, occasionally forcing them to abandon the breeding area (Burger and Shisler 1978, Burger 1985). In addition, larger larids generally arrive at breeding sites earlier (Morris and Hunter 1976, Burger 1985), which gives them a competitive advantage over smaller species. Gulls (Larus spp.) frequently have been involved in the displacement of other species from breeding habitats (Thomas 1972, Burger 1979, Bradley and Monaghan 1986, Furness and Monaghan 1987). Terns appear to be one of the most affected seabirds, and some tern populations have decreased as a result of population expansion by gulls (Thomas 1972, Nisbet 1973, Greenhalgh 1974, Courtney and Blokpoel 1983, Parnell et al. 1988, Ainley and Hunt 1991, Blokpoel and Scharf 1991). At Punta Le6n, Argentina, Royal Terns (Sterna maxima) and Cayenne Terns (S. eurygnatha) breed intermingled in a dense cluster of nests within a Kelp Gull (Larus dominicanus) colony. The Kelp Gull colony increased in size from 3,200 pairs in 1982 to 6,500 in 1995, and gulls currently occupy almost all of the available nesting space (Yorio et al. 1994). Given the overlap in nest-site use and the current expansion of Kelp Gulls, we expected that competition for nesting space could result in negative effects on both species of terns. In this paper, we document spatial interactions between Kelp Gulls and Royal and Cayenne terns at Punta Le6n, Patagonia. We

Predation by Kelp Gulls Larus dominicanus at a mixed‐species colony of Royal Terns Sterna maxima and Cayenne Terns Sterna eurygnatha in Patagonia

We studied the predator‐prey interaction between Kelp Gulls Larus dominicanus and Royal Terns Sterna maxima and Cayenne Terns Sterna eurygnatha at Punta León, Argentina, from 1990 to 1992. Kelp Gulls were the main predator of tern eggs in all 3 years, accounting for 99% of observed predations (n = 454). A total of 99% of predations occurred on peripheral tern nests. Total predation rate on both tern species was highest in 1990 and varied significantly between years, with between 0.01 and 0.03 cases of predation per hour. Predation rates in all years were significantly higher on Cayenne than on Royal Terns probably because the latter were significantly more aggressive towards gulls than were Cayenne Terns. Royal and Cayenne Terns displayed aggressively towards gulls at least once in 64% and 10% of the observation periods, respectively. Defence behaviour, such as attacking and chasing the predator, was used more frequently by Royal than Cayenne Terns (13.2% v 3.6%). Predation on tern eggs was restricted to only a few Kelp Gulls which nested close to the tern colony periphery, and 50% of the eggs that were stolen were taken by only two pairs during 1991 and 47% by three pairs in 1992. This suggests that the current expansion of the Kelp Gull numbers at Punta León might not necessarily result in a proportional increase in predation rate on both tern species. Stealing eggs from the ground was more successful than from the air (77% v 17%). The nesting strategy shown by Royal and Cayenne Terns at Punta León appears to be an important factor which reduced the impact on their breeding success of high potential predation pressure by gulls.

Effects of Varied Electrophoretic Conditions on Detection of Evolutionary Patterns in the Laridae

The extent and effects of hidden variation on detecting evolutionary patterns in the family Laridae were examined using sequential starch-gel electrophoresis of proteins. To determine whether more alleles were hidden at higher taxonomic levels than within species, 25 individuals of Sternaforsteri and 20 species in the family Laridae were analyzed. Varied conditions detected two hidden alleles in the 25 S. forsteri, whereas 26 alleles were hidden across the 20 larid species. These alleles were hidden using buffer conditions not commonly employed in avian electrophoretic surveys and had no effect on phylogenetic reconstruction. Distance-Wagner analysis showed the following to be distinct groups: (1) Rynchopinae, (2) Stercorariinae, (3) Anous stolidus, (4) Larinae, and (5) Sterninae. Within the Sterninae, S. antillarum and Chlidonias niger are the most divergent. Sterna maxima and S. forsteri are sister taxa, as are S. nilotica and Phaetusa simplex. Sterna hirundo and S. vittata show no differences at the 23 loci examined, which does not support the hypothesis that S. vittata arose from a migrant population of S. paradisaea that remained in the Antarctic. Cladistic analysis provides evidence that A. stolidus, placed with the Sterninae under all classification schemes, is indeed a tern, but may be evolving faster than other terns. The results of this study agree generally with a morphometric analysis of the Laridae by Schnell (1970a, 1970b).

Mauritania: its wildlife and a coastal park

Most of Mauritania's populations of large mammals have been exterminated or severely depleted by hunting. The Mauritanians usually do not hunt birds, however, and as a result the avifauna are protected, albeit somewhat passively. The Parc National du Bane d'Arguin is an exceptionally rich coastal area, attracting huge concentrations of waders in the European winter and impressive nesting colonies of birds in the summer, including eastern white pelicans, greater flamingos and royal terns. Although the birds are probably safe, the Park's mammals are not, and the last few dorcas gazelles need urgent protection from poachers.

Nest Site Selection by Laughing Gulls: Comparison of Tropical Colonies (Culebra, Puerto Rico) with Temperate Colonies (New Jersey)

We examined nest site selection in Laughing Gulls (Larus atricilla) nesting on three islands in the Culebra National Wildlife Refuge, Puerto Rico, to determine if gull nest sites showed consistent characteristics differing from most of the available habitat, to compare nest site characteristics on islands with different vegetative cover, and to contrast nest site choices on these tropical island colonies with colonies that we have studied on the northern Atlantic coast of mainland United States. At Culebra, Laughing Gulls nested with Royal, Sandwich, and Bridled terns (Sterna maxima, S. sandvicensis, S. anaethetus), Brown Noddies (Anous stolidus), and Brown Boobies (Sula leucogaster), but their nearest neighbors were usually conspecifics. The gulls' nest sites generally differed from random points with respect to percent cover, vegetation height, visibility, and distance from clearings. Compared to the random points, gull nests were under denser vegetation of intermediate height with high visibility from their nests and with less cover around their nests. Their choice of nest sites provided protection and cover from predators and the sun. Dense and tall vegetation would hinder gulls from flying directly from their nests, and many nests were thus near rocks or clearings, which allowed the gulls to exit quickly. Laughing Gulls nesting on the Culebran cays generally nested in taller, denser vegetation than those nesting farther north along the Atlantic coast, which partially reflects temperature differences between the localities.

Taxonomy and Conservation of Austral-Breeding Royal Terns

Taxonomy and Conservation of Austral-Breeding Royal Terns

Bird mortality at a power transmission line in Northeastern Venezuela

Abstract A survey of bird casualties resulting from collisions with cables in a section of the Margarita power transmission line at Chacopata Lagoon, northeastern Venezuela, where it runs between two expanses of water, was undertaken on 27 February 1983. A total of 611 birds skulls and freshly killed or crippled birds belonging to 10 species were counted. Brown pelicanus Pelecanus occidentalis, neotropic cormorants Phalacrocorax olivaceus, royal terns Sterna maxima, and black-crowded night-herons Nycticorax nycticorax, listed here in decreasing order of abundance, suffered the heaviest losses. The frequency of collisions with the power line is discussed in function of the species composition in the bird community, the behaviour of the birds, the flight characteristics or flight directions, the familiarity with local features, and the interactions with local fishermen and poachers. Undetermined quantities of casualties resulting from the removal of carcasses by scavengers appear more significant in smaller species, whereas those resulting from the hiding of injured birds seems to be more significant in larger species. Most collisions with the power line apparently occur either at dusk or at dawn. Burying of the cables is considered as the best corrective measure to prevent bird mortality in this case.

Bioaccumulation of lead and cadmium in the Royal Tern and Sandwich Tern.

Lead and cadmium concentrations were measured in eggs and tissues of downy young, prefledgling, and adult Royal and Sandwich Terns collected from Galveston Bay, Texas. These species do not differ significantly in the amount of heavy metals they accumulate; however, they differed from other species of the same trophic level from Galveston Bay in degree and pattern of temporal accumulations of these metals. Lead levels were lower in terns, but cadmium levels in adult terns were higher than those of other species. The prefledglings of other species at this trophic level have lead and cadmium concentrations which are similar to those found in adults. In contrast, the concentrations of the metals in adult terns are markedly higher than those found in prefledgling terns. This suggests that accumulation of metals continues as the birds age.

Relation of environmental factors to breeding status of royal and sandwich terns in South Carolina, USA

The population ecology of the royal tern Sterna maxima and sandwich tern Sterna sandvicensis was investigated in South Carolina from 1970 through 1977. Royal and sandwich terns nested together in all of the colonies that we located. The peak in egg laying usually occurred in early May; peak hatching occurred from late May to mid-June. Clutch size for both species was one egg. Tidal flooding was the major factor in egg loss. The breeding population was 15,499 pairs in 1974 and 18,096 pairs in 1975; sandvicensis made up about 5% of the breeding population. The average number of young fledged per nest ranged from 0·36 to 0·44. Residues of organochlorine pollutants in most eggs and tissues were low and posed no identifiable threat to the terns. There was a decline in DDE and dieldrin residues in eggs of maxima. The future of royal and sandwich terns in South Carolina seems fairly secure as the population is apparently at or near carrying capacity and most of the major nesting sites are dedicated to protection of nesting birds.

Responses of Barn Swallows to Eggs, Young, Nests, and Nest Sites

Aspects of egg, young, nest and nest site recognition have been investigated or observed in several species of birds (e.g., Cullen 1957, Davies and Carrick 1962, Beer 1969, Peek et al. 1972). In general, selection appears to favor recognition of as few characteristics as necessary to insure a high probability of caring for the correct eggs or young. Birds that build nests respond to their nest sites, and later their young (usually when mobile), but show little evidence of specifically recognizing their own nests or eggs (Nice 1943, Tinbergen 1953, Beer 1970). Common Murres (Uria aalge; Johnson 1941, Tschanz 1959), which do not build nests, and Royal Terns (Sterna maxima; Buckley and Buckley 1972), which nest in dense colonies where their eggs may be displaced, recognize both their eggs and laying sites. Among passerines, Rothstein (1975) found that some species (rejector species) can recognize foreign eggs placed in their nests, while others (acceptor species) do not. Bank Swallows (Riparia riparia; Hoogland and Sherman 1976), Red-winged Blackbirds (Agelaius phoeniceus; Peek et al. 1972), and Carrion Crows (Corvus corone; Yom-Tov 1976) do not discern their eggs, or their young until near fledging, at an age when an error in progeny care is possible. Tricolored Blackbirds (Agelaius tricolor), which nest in dense colonies, accept eggs or young placed in their nests (Emlen 1941). Many non-passerines are similar in their varied ability to recognize their eggs or young (Tinbergen 1953, Davies and Carrick 1962, Beer 1970). Red-winged Blackbirds recognize their nest sites specifically, but accept substitute nests (Peek et al. 1972). Nero and Emlen (1951) found that female Red-winged Blackbirds would follow displaced nests even across territorial boundaries of males. Meise (1933) moved the nest of a House Sparrow (Passer domesticus) 1.5 m and observed no response to it by the adults. Among non-passerines, a Cooper's Hawk (Accipiter cooperii) nest moved in small increments from its original location in the crotch of a tall tree to a bushel basket, and then to the ground, was accepted at each step by the adults (Allen 1951). Herring Gull (Larus arg ntatus) nests moved about 30 cm were accepted if they contained eggs and the original nest site was covered with sand (Tinbergen 1953). In experiments with Sooty Terns (Sterna fuscata), birds returned to their nest sites rather than to nests displaced short distances (Lashley 1915). From these studies, it appears that selection favors more rigid responses to changes in nest and nest site for colonial than for non-colonial species. In the present study, I evaluated responses of Barn Swallows (Hirundo rustica) to their eggs, young, nests, and nest sites. Barn Swallows are facultative colonial nesters and unique among the above species in that their colonies are passive aggregations of birds (Snapp 1976). Barn Swallows have recently used man-made structures for nesting (Bent 1942), and such behavior may influence the size of their aggregations. Do swallows respond to aspects of the nesting situation in the same way as colonial or noncolonial species?

SEABIRDS OF THE SENEGAL UPWELLING AND ADJACENT WATERS

SUMMARYSeabird distributions were observed off Senegal during the upwelling season there, in February‐March 1976, and are interpreted against an oceanographic background. Gannets Sula bassana, Pomarine Skuas Stercorarius pomarinus, Great Skuas Catharacta skua, Lesser Black‐backed Gulls Larus fuscus, Black‐headed Gulls L. ridibundus, Sandwich Terns Sterna sandvicensis and Royal Terns S. maxima were the dominant species on the shelf and slope adjacent to the inshore upwelling zone. Grey Phalaropes Phalaropus fulicarius were the only seabirds associated with an oceanic ‘front’ farther offshore; it is suggested that this and similar boundary zones are important feeding areas during the pelagic phase of this species' annual cycle.Leach's Storm‐Petrels Oceanodroma leucorhoa were seen east to 20W, but the predominant storm‐petrel of the waters between 23W and the continental slope was the Madeiran O. castro. It is suggested that the hatching period of Madeiran Storm‐Petrels on the Cape Verde Islands is timed to take advantage of the arrival there of young fish in the surface waters, spawned off the African coast and drifted offshore. However Madeiran Storm‐Petrels make no direct use of the coastal upwelling; nor do Little Shearwaters Puffinus assimilis or White‐faced Storm‐Petrels Pelagodroma marina, the other winter‐breeding Cape Verdes seabirds, which probably feed close to the Islands.The Senegal upwelling is underexploited by seabirds, in contrast to comparable upwelling systems elsewhere. It is suggested that this is due to the seasonal timing of the upwelling, the scarcity of secure nest‐sites for breeding seabirds, and the competing attractions of the Benguela upwelling in the South Atlantic.

Coloniality in Terns: The Role of Social Feeding

Coloniality in ground-nesting seabirds is believed by most workers to have evolved primarily as an adaptation to avoid predation (Tinbergen 1953, Cullen 1960, Kruuk 1964, Lack 1968). Because locations free of mammalian predators are limited, many marine species breed in dense congregations. Birds in large breeding colonies may effectively reduce avian predation either because many individuals jointly mob an intruding predator (Kruuk 1964) or because nests in the center of the colony are relatively invulnerable to predators (selfish herd phenomenon of Hamilton 1971). The upper limit in colony size is presumably set by food supply (Ashmole 1963, Bourne 1963, Lack 1968, Nelson 1970). Recent evidence suggests that food-finding is another important function of coloniality (Ward 1965, Horn 1968, Fry 1972, Ward and Zahavi 1973, Krebs 1974, Emlen 1975). When food is unevenly distributed and unpredictable, individuals may learn about good feeding sites by observing the flight direction and success of individuals nearby (Turner 1964). In this view, colony size per se might be an important selective factor because large colonies provide more sources of about food location than small ones. Ward and Zahavi's (1973) informationcentre hypothesis predicts that, given equal habitat and predation factors, species which depend upon food that is unpredictable in space and time and/or distributed over large areas should nest in larger colonies than species feeding on a more uniformly-distributed food source close to the nest site. Also, gregariousness and group feeding should be more highly developed in species relying upon local enhancement (Thorpe 1956) to find dispersed food patches over large feeding areas. To test the hypothesis, I compared the six abundant beach-nesting tern species along the Atlantic coast of the United States: Arctic Tern (Sterna paradisaea), Common Tern (S. hirundo), Roseate Tern (S. dougallii), Least Tern (S. albifrons), Royal Tern (S. maxima), and Gull-billed Tern (Gelochelidon nilotica). Sandwich Terns (S. sandvicensis) were not included because of their low numbers and the lack of information about their feeding ecology. Five of the six species are primarily piscivorous (i.e., all except Gull-billed Terns), and all nest primarily on beaches or rocks of open islands. Breeding space seldom appears to be limited and most colonies are on sites

Ruptured-Yolk Peritonitis and Organochlorine Residues in a Royal Tern

Ruptured-yolk peritonitis was responsible for the death of a royal tern. Lodgment of eggs in the oviduct was probably due to reverse peristalsis brought about by breakage of the thin-shelled eggs and secondary bacterial infection. The thin shells were apparently not related to the low levels of DDE and other organochlorine pollutants found in tissues and egg contents.

Foraging and Breeding Adaptations to Different Food Regimes in Three Seabirds: The Common Tern, Sterna Hirundo, Royal Tern, Sterna Maxima, and Black Skimmer, Rynchops Niger

Aspects of foraging and breeding ecology of the Royal Tern, Sterna[=Thalasseus]maxima, Common Tern, Sterna hirundo, and Black Skimmer, Rynchops niger, were compared in light of the food resource. Field studies conducted in 1973 and 1974 in the USA on two of Virginia's barrier islands revealed that the three species differed markedly in foraging ranges and habitat use, social feeding tendencies, and colony sizes and distribution. The investigation was designed to examine how these behavioral and ecological differences are related to the different regimes of food patterns. Analysis of beach seine records from inshore (< 50 m) waters were contrasted with haul seine and trawl collections from offshore (> 3 km) waters from both the Eastern Shore of Virginia and the Delaware Bay. Spatial variability (between sampling site variation) was found to be much greater offshore than inshore, indicating greater ‘patchiness’ of fish. Also, the availability of surfacing fish appeared to fluctuate markedly over time. In response to these food regime differences, Royal Terns, which feed further from the colony than common Terns and Black Skimmers, (1) readily formed feeding aggregations, (2) showed large daily variability in feeding the young, and (3) were the most ‘colonial’ in nest—spacing, colonial size and distribution. The strictly inshore—feeding skimmers usually fed alone, show little variability in feeding, and formed the ‘loosest’ colonies of the three species. Common Terns were intermediate in all respects. The differences in the ‘colonial tendencies’ among the species are consistent with the predictions of two earlier models relating breeding assemblages and food distribution.

Eggshell Removal by Laughing Gulls

After hatching of their young many birds either cat eggshells or remove them from the nest. This and other nest sanitation behavior,such as defecation flights from the nest and the ingestion or disposal of nestling excrement, arc found among a variety of birds (Blair and Tucker, 1941; Nethersole-Thompsona nd Nethersole-Thompson, 1942). With some exceptions, e.g., Kittiwakcs (Rissa tridactyla; Cullen, 1957), Sandwich Terns (Sterna sandvicensis; Cullen, 1960; Crozc, 1970), Royal Terns (S. m. maxima; Bucklcy and Bucklcy, 1972), most Laridae tend to remove eggshells from their nests. Tinbergen et al. (1962) concluded that in Black-headed Gulls (Larus ridibundus) eggshell disposal represents a behavioral component of camouflage, i.e., removing conspicuous objects(white shell membranes)that might attract avian predators to the nest. The present experiment investigated the responsiveness of Laughing Gulls (Larus atticilia) over the course of a nesting cycle to an eggshell on the nest rim.

Comparative Feeding Ecology of Wintering Abult and Juvenile Royal Terns (Aves: Laridae, Sterninae)

Comparison of the feeding behavior of adult and juvenile Royal Terns, Sterna maxima, showed the following: adults spent less time foraging over a given stretch of beach, making almost twice as many dives per minute as juveniles; while initial prey capture rates were the same on both age—classes, adult dived more frequently, and therefore caught more prey per unit time; both rarely dropped their prey without recovering it, but juveniles dropped their prey, subsequently recovering it, almost 14 times as often as adults, thereby expending considerably more energy per prey capture than adults. Analyses of counts of sitting and feeding terns confirmed predicted nonrandom associations: feeding adults avoided all other birds except their offspring, but, when resting, avoided even juveniles more often than expected; feeding juveniles occurred almost equally frequently alone, with adults, and in small flocks (adults never so occurred). An attempted time—budget analysis, limited by unmarked birds, suggests that adults feed more in the early morning hours, resting or foraging for their young later in the day; juveniles apparently do most of their solo fishing between 0900 and 1200 h, and in general spend less day time roosting than do adults. Analysis of data on recovered, banded terns indicate that significantly more juveniles than adults are caught on fishhooks and that adults' ability to recognize capturable prey is a prime factor in their fishing success. These results confirm Lack's and Ashmole's basic hypothesis that extended parental care and reduced feeding ability of young have played a significant role in the evolution of seabird clutch size. Considered in terms of the Holling—Griffiths—Watt "components of predation" analysis, our data suggest that these foraging differences must be incorporated in future predatory—prey models. The component analysis approach ought to be extended to other terms, especially over longer periods of time post—fledging. Salt and Willard's conclusions from their component analysis of the foraging behavior of Forster's Tern, reexamined in the light of our findings, lead us to believe that insufficient data are available to decide whether Forster's and Royal Terns better fit Holling—Griffiths—Watt or Lotka—Volterra predator—prey models, because these models fail to consider important aspects of the terns' biology and because certain data needed for their use were not obtained in either study.

SEA‐BIRDS AT LAGOS AND IN THE GULF OF GUINEA

SummaryRegular observations of sea‐birds were made in the vicinity of Lagos, southwest Nigeria, between October 1967 and June 1971. Records in the Gulf of Guinea were obtained in April 1969 and, together with others from Ghana and Sierra Leone, were used to complement this study. While few large populations of sea‐birds are supported, the diversity of species occurring at Lagos and over offshore deep water was great. The occurrence of nine species of sea‐bird new to Nigeria was established or confirmed; most of these were also new to West Africa southeast of Gambia. Details are given of fluctuations in numbers these and a further 16 species.All coastal habitats at Lagos supported a large population of immature Black Terns, and groups of immatures made up a high proportion of observations of other Palaearctic terns and of Royal Terns, which breed only in northwest Africa. In contrast, the Lesser Black‐backed Gulls and Damara Terns reaching Lagos (from breeding grounds almost two continents apart) were mainly adults; both these species are amongst those showing a current increase in numbers. A pronounced spring passage was observed among species including Royal and Sandwich Terns, but adult movements in autumn were not elucidated. The occurrence of the European race of the Little Tern in southwest Nigeria was confirmed, it is at least a regular spring migrant. The frequency of vagrants in January and February was linked to local climate as much to general distribution. Brief comment is also given on immature plumages, and the growing exploitation and pollution of coastal waters.

Individual egg and chick recognition by adult royal terns ( Sterna maxima maxima)

Egg-switching choice experiments involving forty-two adult royal terns in eight choice situations at Hatteras Inlet, North Carolina, revealed that incubating adults consistently recognized their own single egg when placed in a wrong but adjacent nest. Individual egg colour and marking differences probably play the major role, but features of nest site (and/or of adjacent adults) were also shown to play a significant role in recognition and settling. Only two chick-switching experiments were done, with four chicks. Three of the returning adults failed to recognize their own chicks until the latter vocalized; the fourth recognized its silent chick and called it away from the nest site. The adaptive value of individual recognition of eggs and chicks is considered for this group (Thalasseus) of densely nesting, creche-forming terns.

THE BREEDING ECOLOGY OF ROYAL TERNS STERNA (THALASSEUS) MAXIMA MAXIMA

SummaryThe breeding ecology of the New World race of the Royal Tern Sterna maxima maxima was studied at colonies in Virginia and North Carolina, U.S.A., from 1967 to 1970.Colony sites are quite varied, but isolation, good distance visibility and (especially) freedom from quadruped predators seem important if not essential prerequisites.In Virginia, most adults arrive at the colony site in the last few days of March. Courtship, displaying and copulation take place at, near, and some distance from the colony site. In this the Royal Tern differs from its near relative S. sandvicensis sandvicensis which carries out these activities away from the colony site, presumably as an anti‐predator device.Courtship displays are not described, but in their essentials are similar to those of other terns. Copulations continue throughout incubation and gradually disappear when the eggs hatch. No post‐copulatory displays are known. Some synchrony of egg‐laying is evident, but no “mass laying” occurs, the colony increasing in size steadily over a period of weeks and months. Defaecation on the nest is normal and probably serves to strengthen the nest rim against flooding by high tides.Contrary to published reports, the normal clutch is one; the largest is two, probably often from two different females. All incubating adults examined had two brood patches.Average egg measurements are 63 × 44‐5 mm, and average egg weight is 64.3 g. Egg colour varies greatly, and evaluation is difficult. Eggs are probably not cryptically coloured and individual variation, as well as nest‐site, are used by returning adults to identify their own eggs.Average maximum nest density is c. 7/m2. Sterna sandvicensis acuflavida nests regularly, if not obligatorily, with m. maxima; interactions between the two, and possible benefits accruing to each, are discussed. Unhatched eggs were significantly nearer other nests than were successfully hatched eggs, and possible explanations are given.Incubation lasts about 30–31 days, a week longer than in most terns; both sexes incubate.Broken eggshells are never removed by the adults. Instead, after 2–3 days, the chicks leave the nest permanently to join a creche that roams freely about the immediate vicinity of the colony. Chicks remain in the creche for about 25–30 days, leaving it at fledging, approximately 30 days after hatching.While in the creche, chicks are normally fed only by their parents, who probably recognise them both vocally and visually, using the extensive variation in voice and colour of chicks characteristic of the species. Sandvicensis acuflavida chicks also are highly variable, and join Royal creches, adults of both species attending. Variation also occurs in Royals' juvenal plumage, and seems associated with extended parental care.Feeding adults normally wander up to 40 km from their colony, and this probably facilitates the intercolonial exchange of breeding birds we recorded. They feed inshore, in shallow waters, taking small fish by dives which do not go below the surface. They regularly take small soft‐shell crabs in this way, and frequently water‐skim like skimmers Rynchops spp., sometimes capturing food while doing so. A relationship between crab capture and water‐skimming is established for the first time, and water‐skimming in non‐feeding contexts is mentioned.Besides the quadruped predators which they normally avoid by fleeing the colony site, Royals have no known predators beyond the egg stage. Eggs, although not chicks, are readily taken by Laughing Gulls. Relationships between the two species are discussed, emphasising their constant association the year round.

Notes on the Royal Tern in Surinam

Journal Article Notes on the Royal Tern in Surinam Get access F. Haverschmidt F. Haverschmidt Wolfskuiktraat 16 Ommen, Holland Search for other works by this author on: Oxford Academic Google Scholar The Condor, Volume 72, Issue 2, 1 April 1970, Page 246, https://doi.org/10.2307/1366653 Published: 01 April 1970 Article history Accepted: 21 February 1969 Published: 01 April 1970