Ground-nesting Seabirds Research Articles

Temporal variations in the concentration and isotopic signature of ammonium- and nitrate–nitrogen in soils under a breeding colony of Black-tailed Gulls (Larus crassirostris) on Kabushima Island, northeastern Japan

Abstract Temporal variations in the concentration and N isotopic ratios of inorganic N (NH4– and NO3–N) as affected by the soil temperature regime together with the input of bird excreta were analyzed in a sedentary soil under a dense colony (1.6 nests/m2) of breeding Black-tailed Gulls (Larus crassirostris: a ground-nesting seabird). Surface soil samples were taken monthly from mid-March to late July 2005 from Kabushima Island, Hachinohe, northeastern Japan. The spatial concentration of inorganic N in the soils varied considerably on all sampling dates. There may be a statistically significant trend, showing increased NH4–N content from settlement up to early June when the input of fecal N attains its maximum, and then decreases towards the end of breeding activity (early August). Abundant NO3–N was observed in all soils, particularly in the later stage of breeding (up to 3800 mg-N/kg dry soil), refuting earlier claims that nitrification is unimportant in the soils. δ15N values of NH4 in the soils showed unusually high values up to +51‰, reflecting N isotope fractionation due to volatilization of NH3 during the mineralization. Mean δ15N values of the monthly collected totals of NH4 and NO3 were not significantly different at the 5% level based on ANOVA and significant differences were observed only among the three means of NO3–N collected in mid-March (settlement of colony: δ15N = −0.2 ± 3.5‰) and late July (later stages of breeding: δ15N = +22.1 ± 7.0‰, +23.3 ± 7.8‰) at the 1% and 5% levels by t-test, respectively. Such an observation of significantly increased δ15N values for NO3–N in soils from the fledgling stage indicates the integration of denitrification coupled with nitrification under a limited supply of fecal N.

Severity of the Effects of Invasive Rats on Seabirds: A Global Review

Invasive rats are some of the largest contributors to seabird extinction and endangerment worldwide. We conducted a meta-analysis of studies on seabird-rat interactions to examine which seabird phylogenetic, morphological, behavioral, and life history characteristics affect their susceptibility to invasive rats and to identify which rat species have had the largest impact on seabird mortality. We examined 94 manuscripts that demonstrated rat effects on seabirds. All studies combined resulted in 115 independent rat-seabird interactions on 61 islands or island chains with 75 species of seabirds in 10 families affected. Seabirds in the family Hydrobatidae and other small, burrow-nesting seabirds were most affected by invasive rats. Laridae and other large, ground-nesting seabirds were the least vulnerable to rats. Of the 3 species of invasive rats, Rattus rattus had the largest mean impact on seabirds followed by R. norvegicus and R. exulans; nevertheless, these differences were not statistically significant. Our findings should help managers and conservation practitioners prioritize selection of islands for rat eradication based on seabird life history traits, develop testable hypotheses for seabird response to rat eradication, provide justification for rat eradication campaigns, and identify suitable levels of response and prevention measures to rat invasion. Assessment of the effects of rats on seabirds can be improved by data derived from additional experimental studies, with emphasis on understudied seabird families such as Sulidae, Phalacrocoracidae, Spheniscidae, Fregatidae, Pelecanoididae, Phaethontidae, and Diomedeidae and evaluation of rat impacts in tropical regions.

Impact of Raccoons on Breeding Success in Large Colonies of Great Black-backed Gulls and Herring Gulls

For most ground-nesting seabirds, offshore islands usually serve as refuges from mammalian predators, however, introduced predators pose a substantial threat to many species. In New England, thousands of Herring Gulls (Larus argentatus) and Great Black-backed Gulls (L. marinus) breed on hundreds of coastal islands. The Isles of Shoals (New Hampshire/Maine) archipelago has some of the largest colonies of both gull species in New England. In 2004, we noted unusually large numbers of failed nests on Appledore Island, Maine and hypothesized that Raccoons (Procyon lotor) were the cause. Therefore, we quantified egg and chick mortality and documented the presence of Raccoons. We trapped Raccoons on Appledore and Smuttynose islands and conducted nest surveys on these and two other islands in the Isles of Shoals. Surveys of marked nests on Appledore Island revealed high levels of egg and chick mortality in early June 2004; by late June 58% of nests were empty. We also found that on Appledore and Smuttynose, where Raccoons were observed, the odds that a nest would be empty were 17 times greater than on Lunging or Duck Islands where no Raccoons were observed. During 2004, eleven Raccoons were trapped off of Appledore and Smuttynose Islands. A survey of nests in 2005 showed that gull breeding success increased significantly on Appledore and Smuttynose islands, whereas there was no significant change in the relatively high ratio of chicks to nests from 2004 to 2005 on Lunging Island where Raccoons were not observed. Thus, we concluded that the presence of a few Raccoons on Appledore and Smuttynose islands was sufficient to cause substantial breeding failure in large colonies of larids.

Dispersal and germination of seeds of Pisonia grandis, an Indo-Pacific tropical tree associated with insular seabird colonies

The distribution of the forest tree Pisonia grandis (Nyctaginaceae) coincides with seabird colonies on small tropical islands. Its seeds are enclosed in a calyx exuding extremely sticky resin which adheres strongly to feathers. Birds are obviously seed-dispersal vectors, but the multi-seeded infructescences frequently entangle birds, often fatally. On Cousin Island, Seychelles, I investigated the production, germination, survival, and tolerance to seawater of Pisonia seeds, and the occurrence of entanglement with birds. Fresh seeds had high germination success (62–87% in experimental trays), but seedling survival in Cousin's forests was low (0.1% of 6020 seeds survived as seedlings after 2–8 mo). Some seeds tolerated 30 min daily immersions in seawater (8–15% germination after 14–28 d treatment), but not continuous immersion in seawater (reduced germination after 5 d and none after 12 d). Inter-island dispersal is likely via living unencumbered seabirds carrying a few seeds, but not on floating carcasses. Seeds attached to carcasses did not have improved germination or survival. Intra-island propagation is almost entirely vegetative, with negligible local seed dispersal. Pisonia plants therefore do not benefit from fatal entanglements. The extreme stickiness of the seeds evidently evolved to resist removal by seabirds and so facilitate long-distance dispersal. The mortality of some potential vectors is an unfortunate consequence, but has little impact on the large populations of tree- and ground-nesting seabirds which nest in or under these trees.

Testing the intergenerational conflict hypothesis: factors affecting adoptions in Audouin's gulls, Larus audouinii

We studied chick adoption in Audouin's gull, Larus audouinii, a ground-nesting seabird, to test several predictions made by the intergenerational-conflict hypothesis (ICH). The effects of food availability on adoptions were considered by comparing two breeding seasons with differing food supply. As predicted, adoptions were significantly more frequent when food was in shorter supply (48% of broods affected) than when it was more available (18.5%). Adoptions occurred during the first week of the chick-rearing stage; after that, aggression by adults towards intruding chicks increased significantly, which suggests that mechanisms of parent-offspring recognition were established. Foster parents incurred certain costs, since their offspring had lower chances of survival than those in control broods. However, contrary to the ICH hypothesis, adoptees did not select foster broods in relation to the age of the resident chicks. Survival of wandering chicks was no higher than that of chicks who stayed in their natal brood. Results suggest that chicks move only as a response to neighboring chicks being fed by an adult, and in Audouin's gulls, adoptions might be considered reproductive errors.

Food availability and nest predation influence life history traits in Audouin's gull, Larus audouinii.

The effects of food availability and nest predation on several life history traits such as adult survival, dispersal, and reproductive performance were assessed in an Audouin's gull (Larus audouinii) colony during the period 1992-1997. The amounts of fish discarded from trawlers were used as a measure of food availability, and a trawling moratorium which partially overlapped with the breeding season of the gulls was taken into account. The effects of nest predation were assessed in 1994, when a terrestrial predator entered the colony and remained for the whole breeding season preying on both eggs and chicks. Using the moratorium and the predatory event as natural experiments, several hypotheses were tested: (a) food supply would affect breeding performance but not adult survival (independently of age and sex), since gulls are long-lived and adult survival is the most sensitive demographic parameter in their population dynamics; (b) the predator would trigger breeding dispersal (although gulls are mostly philopatric, they are known to abandon their natal colony after breeding failure instigated by events such as this). If breeding dispersal occurs, the rate is expected to be higher in females than in males, and higher in new breeders than in more experienced breeding birds, as is usually recorded in colonial seabirds. Probabilities of resighting and survival were estimated separately, using capture-recapture models. As expected, changes in food availability did not affect adult survival, whereas they influenced egg volume, clutch size, and breeding success. Local adult survival was estimated to be 0.908 (SD = 0.007) for males and females, and it did not change significantly with the age of individuals (range 3-8 years). The predator significantly decreased breeding success, and caused the dispersal of a number of adults probably to breed in another colony; this rate was estimated at an average of 0.10 (SD = 0.02). As expected, inexperienced breeders dispersed significantly more (14%) than more experienced breeders (8%) after the predator event, but dispersal was not sex biased. Recapture probabilities after the predator event suggest that birds that left the colony still had not returned. Results confirm that population dynamics of ground-nesting seabirds are sensitive to terrestrial predation, even when predation caused only a partial breeding failure.

The fossil birds of Henderson Island, Pitcairn Group: natural turnover and human impact, a synopsis

Abstract Recent studies of island biotas have suggested that the impact of man on indigenous flora and fauna is much greater than previously suspected. This impact resulted in the introduction of many new species and the extinction of many unique life-forms. Henderson Island, in the Pitcairn Group, has been found to be an excellent laboratory for the study of natural faunal turnover and the impact of people on the natural environment. This was principally due to the island's remote location and its limestone structure, which resulted in the excellent preservation of fossil remains. During the Sir Peter Scott Commemorative Expedition to the Pitcairn Islands, extensive excavations were undertaken resulting in the collection of 42 213 bird bones. It was possible to identify 31%. Of the 31 taxa identified, four seabirds appear to be vagrants, a surprisingly high number illustrating that the uncritical evaluation of fossil bird lists from other islands risks over-estimating the number of indigenous species. As a result of the arrival of Polynesian people during the first half of this millennium, half of Henderson's endemic landbirds became extinct, as did most of the small ground-nesting seabirds. The lower sea level during cold stages creates many temporary limestone `high' islands. This results in many `former-atolls' developing geological and ecological similarity to Henderson. Hence lower sea-level greatly facilitates the movement of flora and fauna between currently isolated oceanic `high' islands.

Dynamic ecology of Aldabran seabird communities

The characteristics of the present seabird community of Aldabra are described, and compared briefly with others in the tropics. By comparison with Pacific Ocean communities, Aldabra is deficient especially in petrels and shearwaters, which are poorly represented in the western Indian Ocean generally and are absent probably for zoogeographic reasons. Ground-nesting species are also scarce, especially pelagic feeders that form large colonies, and this is attributed partly to their extermination by rats and partly to the proximity of Assumption, and perhaps Cosmoledo, that offer better nesting sites to these species. Inshore-feeding terns are also scarce on Aldabra, probably owing to insufficient areas of shallow water nearby. Relative population sizes are roughly in agreement with those that would be predicted, except for the fairy tern whose population may have been reduced in the past by barn owls. Almost all Aldabran seabirds nest either in mangroves or on small lagoon islets, the habitats in which birds are least vulnerable to introduced rats, which appear to have had a major effect on nesting distribution. The seabird community is made up of two different trophic guilds, the pelagic feeders which bring in nutrients entirely from outside the ecosystem, and the inshore feeders which cycle nutrients between the intertidal and inshore parts of the system and the terrestrial part. Both result in a net input of nutrients, in the form of bird droppings, to the terrestrial ecosystem. It is estimated that about 1680 t of food are removed from the sea per year, most of the 105 t of guano resulting being channelled into the intertidal, rather than the terrestrial, parts of the ecosystem. The seabird communities likely to have occupied Aldabra in the past are reconstructed on the basis of the known changes in the atoll’s size and structure during the Pleistocene. At most times there would have been more species of seabird using Aldabra than now, and more of their guano would have passed into the terrestrial ecosystem. Probably the most significant event in the recent history of the atoll was the arrival of rats, which exterminated probably quite considerable colonies of ground-nesting seabirds and drove the survivors into the only places where the rats could not survive - the tall mangroves and the tiny lagoon islets. In so doing, the rats destroyed a significant source of nutrient input to the terrestrial ecosystem, with major consequences for the ecology of the atoll as a whole.

Geomorphology of reef islands, northern Great Barrier Reef

During the 1973 Great Barrier Reef Expedition, 67 reef islands were mapped between latitudes 11° 30' S and 17° S on the Great Barrier Reef. During the mapping, the major topographic, lithological, sedimentological and vegetational features of the islands were distinguished, and their elevations relative to a sea level datum established. The islands themselves were categorized in terms of topographic and vegetational complexity. Previous classifications by Steers, Spender, Fairbridge and others are reviewed in the light of these findings. Some of the islands had been previously mapped by Steers in 1928-29 or 1936; on others, changes could be identified from the evidence of shoreline advance or retreat and from vegetation patterns. The floristics and vegetation units of the islands are briefly described, on the basis of the field mapping and a large collection of flowering plants. Vegetation is influenced by stage in island development, latitudinal variation in rainfall, effects of ground-nesting seabirds, and probably also by disturbance by aboriginal man. Development of mangroves on reef flats is related to stage of reef flat and island development, and relation to tidal levels. This study of the geomorphology of the islands raises questions over the nature, origin and history of specific features (ramparts, beach ridges, boulder tracts, exposed limestones) which the Expedition attempted both to define and to answer.

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

Monitoring Incubation Attentiveness of Ground-Nesting Colonial Seabirds

Monitoring Incubation Attentiveness of Ground-Nesting Colonial Seabirds