Spatiotemporal variation of breeding gull species in a boreal lake complex in Finland: Implications for conservation

Understanding spatial and temporal patterns of species is a prerequisite for successful species and habitat conservation. Spatial variation in breeding sites of four gull species was studied in southern Finland in an oligo-mesotrophic lake complex covering almost 50 km² of water areas and 290 km of shoreline in three census periods in 1986-2004. Two of the species have declined and are regarded as red-listed in Finland (black-headed gull ridibundus and lesser black-backed gull L. f. fuscus) and two have increased (common gull L. canus and herring gull L. argentatus) in numbers during the past decades. The numbers of breeding pairs and the percentage similarity in the spatial distribution of pairs of each species in grid squares were compared between different census periods at resolutions of 0.25, 1 and 4 km². The common gull showed very high percentage similarity between the different census periods and consequently low spatial turnover in nesting sites, whereas the red-listed species, particularly the black-headed gull, had much higher spatial turnover. The spatiotemporal dynamics of gull species should thus be taken into account in conservation planning. If site protection is based only on information of breeding gulls in one year, a large or even major proportion of the breeding red-listed gulls might be outside the protected areas after a few decades. Due to the large spatiotemporal variation of red-listed gulls, areas to be protected should cover a rather large proportion of a boreal lake, not only individual islets or islands.     

Restoration of a multi-species seabird colony

Nesting herring and great black-backed gulls (Larus argentatus and Larus marinus) were removed from a recently abandoned tern (Sterna sp.) colony through a combination of poisoning and shooting. Following gull control, all three species of tern that had nested in the colony prior to the arrival of the gulls returned and nested in increasing numbers. In addition to the restoration of the terns, removal of the gulls led to colonization and/or significant increases in populations of four other seabirds. Gull numbers were greatly reduced by initial poisoning efforts, but continued immigration from surrounding colonies has required an on-going program of shooting to eliminate territorial birds nesting in areas utilized by terns and other species. In situations calling for active management we advocate rapid, focused intervention, and stress the importance of inter-organizational cooperation, and an active program of public education.     

Impact of West Nile virus and other mortality factors on American white pelicans at breeding colonies in the northern plains of North America

American white pelicans (Pelecanus erythrorhynchos) are colonial-nesting birds and their breeding sites are concentrated in a few small areas, making this species especially vulnerable to factors that can influence productivity, such as disease, disturbance, predation, weather events and loss of nesting habitat. Nearly half of the American white pelican population breeds at four colonies in the northern plains: Chase Lake National Wildlife Refuge (NWR) in North Dakota, Bitter Lake (Waubay NWR) in South Dakota, Medicine Lake NWR in Montana, and Marsh Lake in Minnesota. Thus, sustained productivity at these colonies is crucial to the health of the entire species. During the latter half of the 2002 and 2003 breeding seasons, unusually high mortality of pelican chicks was observed at these colonies. West Nile virus (WNv) was identified as one source of these losses. In 2004–2007 we monitored three major colonies in the northern plains to assess mortality of chicks during the late breeding season. We documented severe weather events, disturbance, and WNv as factors contributing to chick mortality. Before WNv arrived in the region in 2002, chick mortality after mid-July was 4%, and then jumped to as high as 44% in the years since WNv arrived. WNv kills older chicks that are no longer vulnerable to other common mortality factors (e.g., severe weather, gull predation) and typically would have survived to fledge; thus WNv appears to be an additive mortality factor. Persistence of lower productivity at American white pelican colonies in the northern plains might reduce the adult breeding population of this species in the region.     

Human interference and gull predation in cormorant colonies

The vulnerability of cormorant eggs and nestlings to gull predation is greatly increased by human intrusion into breeding colonies. Observations of the behaviour of double-crested cormorants (Phalacrocorax auritus) and king shag (P. albiventer) vis-à-vis the behaviour of great black-backed and herring gulls (Larus marinus and L. argentatus) on the one hand and dolphin gulls (Leucophaeus scoresbii) on the other indicate that certain predictable offensive and defensive interactions occur when breeding birds are disturbed. Knowledge of these behavioural patterns suggests that interference with normal breeding activities and the resulting reduction in productivity of cormorants can be minimised in colonies where human access is carefully regulated.     

The conservation status of Townsend's shearwater Puffinus auricularis auricularis

Townsend's shearwater (Puffinus auricularis auricularis) is an endangered seabird endemic to the Revillagigedo Archipelago. It nested on Socorro, Clarion, and San Benedicto Islands. It was extirpated by the Barcena volcano on San Benedicto in 1952, and there are no recent indications of nesting. Introduced mammals—pigs and rabbits—preyed on them and destroyed habitat at Clarion; shearwaters were extirpated by 1988, and no breeding attempts have been reported since. Our results confirm that Socorro holds the last breeding grounds. We found breeding colonies above 800 m and a minimum population of 1100 individuals. This represents a significant reduction in distribution and population size. Intensive cat predation at Socorro could potentially kill ca. 350 females per season, and sheep progressively destroy nesting areas. Population projections suggest that demographic instability could occur in less than 100 years under severe predation and habitat degradation. Only low predation rates would allow population persistence for more than 150 years in spite of a declining population. Thus, the immediate eradication of all introduced mammals is necessary to prevent the extinction of this seabird.     

Evidence-based culling of a facultative predator: Efficacy and efficiency components

Human activities have greatly modified predator-prey dynamics within seabird communities by favouring a rapid increase in density of large predatory gulls. To counteract such a subsidized growth, conservation agencies perform massive random culling programs, which generally fail to restore the original predator-prey relationship. We used long-term individual-based information to evaluate the effects of a selective culling of a top seabird predator, the yellow-legged gull (Larus michahellis), on the predatory pressure, survival and reproductive success probabilities of a secondary prey, the vulnerable European storm-petrel (Hydrobates pelagicus). The selective removal of only 16 gulls in 3 years led to a reduction of ca. 65% in the number of petrels killed, and to a relative increase in their survival and breeding success probabilities of 16% and 23%, respectively. Our results show that only a few specialised predators were responsible for the bulk of the impact on a secondary prey and that the removal of those specialised individuals was an effective and efficient way to improve prey demographic parameters.     

Interference competition in a threatened seabird community: A paradox for a successful conservation

It is often assumed that conservation actions targeting a threatened community (e.g. habitat protection) will result in similar benefits for all species. However, complex interactions between species, such as interference competition, may result in displacement of subordinate, vulnerable species. We analysed here the spatio-temporal population dynamics of a threatened seabird community since the protection in the 1980s of several breeding sites at the Ebro Delta, western Mediterranean, Spain during 1980-2007. Competition for the most suitable patches was governed by body size, with smaller species avoiding associations with larger, dominant species. We tested whether the density increase of the larger species (yellow-legged gull Larus michahellis and Audouin’s gull Larus audouinii) at La Banya (the highest quality patch within the Delta) affected species diversity at the local level. As expected, such diversity decreased, resulting also from the colonisation of other sites by smaller species, some abandoning the former area. The conservation paradox appeared because the interference competition was dominated not only by the largest species of the community, the yellow-legged gull, which is sometimes considered a pest species, but also by the vulnerable Audouin’s gull, a flagship species which has ca. 65% of the total world population at La Banya. Nevertheless, the availability of alternative patches within the Ebro Delta ensured a high biodiversity at regional scale. Results highlight the role of turnover of competing species within a community in ecosystem function and stability, and the importance of alternative sites and dispersal abilities for the conservation of vulnerable communities.     

Is the Yelkouan shearwater Puffinus yelkouan threatened by low adult survival probabilities?

Many seabird species are experiencing population declines, with key factors being high adult mortality caused by fishery by-catch and predation by introduced predators on nesting islands. In the Mediterranean, both of these pressures are intensive and widespread. We studied the adult survival of an endemic Mediterranean seabird, the Yelkouan shearwater (Puffinus yelkouan), between 1969–1994 and 2007–2010 in Malta and between 2004–2010 in France using mark–recapture methods. Mean annual survival probabilities for breeding adults were below 0.9 for all colonies and periods. Between 1969–1994, annual survival for adults of unknown breeding status was on average 0.74 (95% confidence interval: 0.69–0.80) in Malta, possibly as a result of various human disturbances (including illegal shooting), light pollution and fisheries by-catch. Over the period 2004–2010, we found strong support for variation in adult survival probabilities between breeders and non-breeders, and islands with and without introduced predators in France. Survival probabilities for non-breeders (0.95, 0.81–1.0) appeared to be higher than for breeders (0.82, 0.70–0.94), but were imprecise partly due to low recapture probabilities. In Malta, we found evidence for heterogeneity in survival probabilities between two unknown groups (probably breeders and non-breeders), and seasonal variation in survival probability. Birds were more likely to survive the period including the peak breeding season than an equally long period during which they roam widely at sea. Although annual adult survival probability was still low (0.85, 0.58–1.0), colony protection measures appear to have reduced mortality at nesting cliffs. A population model indicated that colonies in France and Malta would currently require continuous immigration of 5–12 pairs per year to maintain stable populations. Our estimates of adult survival probabilities over the past four decades are consistent with overall population declines. Threats to Yelkouan shearwaters require immediate management actions to avoid ongoing population declines in the western Mediterranean.     

A method for assessing the relative importance of seabird breeding colonies

Evaluating the importance of seabird breeding colonies in a national or international context is an essential part of conservation planning. A method for assesiing seabird sites, and for selecting a series of key colonies, is described, following Ratcliffe's (1977) guidelines. The present study uses seabirds in the Republic of Ireland and data recently collected for a breeding seabird inventory. The method is suitable for use on seabird populations elsewhere. The inventory listed over 400 sites, of which 133 were identified by this study to be of national importance to conservation. Among these were 11 internationally important colonies. Thirty-one of the colonies were selected as key sites of special importance.     

Decline in the distribution and abundance of flesh-footed shearwaters (Puffinus carneipes) on Lord Howe Island, Australia

The flesh-footed shearwater (Puffinus carneipes) is a migratory seabird that ranges widely across the Pacific and Indian Oceans. The principal breeding populations are in Australia and New Zealand. The only breeding site in eastern Australia is on Lord Howe Island. Despite it being afforded a high level of legislative protection, the population on Lord Howe Island has declined substantially during the last few decades. The total extent of nesting habitat in 2002 was 24.3 ha, a reduction of 13.4 ha (35.6%) since 1978. Loss of nesting habitat was associated with increased urbanisation, the adverse impact of which extended beyond the footprint of buildings and gardens. In 2002, overall burrow density was 0.123 per m² and the total number of burrows was estimated to be 29,853 ± 5867, a decline of about 19.0% since 1978. A substantial decline in burrow density was evident in the colony where loss of habitat to urbanisation had been greatest. In 2002, 58% of burrows were occupied by breeding birds, and the total population size was estimated to be 17,462 breeding pairs. Breeding success (the proportion of eggs that produced fledglings) was 50%, but was lowest in the most urbanised colony. To avert further declines in the population of flesh-footed shearwaters on Lord Howe Island major changes in land use practices, enforced through appropriate legislation, are needed, together with reductions in the level of seabird bycatch in fisheries operations and in the amount of plastics that litter the world’s oceans.     

The human influence on seabird nesting success: Conservation implications

Based on studies of brown pelicans Pelecanus occidentalis californicus and Heermann's gulls Larus heermanni, disturbances by recreationists, educational groups, local fishermen and scientists alike can be seriously disruptive and damaging to breeding seabirds in the Gulf of California and off the west coast of Baja California. Similar instances have been identified throughout the world—the problem is not difficult to document, but it is difficult to eliminate. The increasing human-seabird contacts on islands in the Gulf of California and along the west coast of Baja California raise serious questions and immediate concern about the continued preservation of nesting colonies of marine birds in those areas. Conservation measures must consider the extreme sensitivity of many seabirds to the inter- and intraspecific behavioural imbalances created by human disturbances. In some cases, total exclusion of humans may be required; in others, limited access might be possible under closely managed conditions at certain times of the year. A symbiotic relationship between seabird conservation, legitimate research and tourism should be the desired goal.     

Status of the Pelecanidae

The recent history, current status and prospects in the immediate future of the seven species of the Pelecanidae are reviewed. As a consequence of pesticide poisoning, Pelecanus occidentalis suffered severe population declines in the 1950s and 1960s in portions of its range in the United States. However, since the ban on use of DDT in 1972 the species is again laying eggs of near normal thickness, reproductive success appears to be normal and populations are stable or increasing. Similarly, available data indicate that the world populations of P. rufescens, P. conspicillatus, and P. erythrorynchos remain stable, although local population fluctuations do occur. Data for P. onocrotalus show a stable population in Africa but a decline in Asia and Europe, both in numbers of birds and breeding colonies. More seriously, only very small populations of P. crispus and P. philippensis exist. Fewer than 1000 pairs of P. crispus next in 19 colonies in eastern Europe and Asia. Fewer than 1200 pairs of P. philippensis nest in four colonies in eastern/southern India and 23 colonies in Sri Lanka. The populations of both species have declined considerably in the past few decades. The causes for the declines are not documented but are thought to result from a combination of human disturbance in nesting colonies; destruction of nesting and roosting-loafing areas; declines in fish availability; and pesticide contamination. Only immediate action and concerted efforts at stabilizing the populations in the wild, in conjunction with the establishment of captive breeding populations, will preserve these two species from extinction.     

Human disturbance and nesting success of Common Eiders: interaction between visitors and gulls

Common Eider colonies often are subjected to human visitors, such as down collectors, recreationists and researchers. However, the effects of frequency and timing of disturbance, and the abundance of nearby avian predators on eider nesting success have been studied only partly. We used three experimental treatments and six eider colonies over 3 years (1993-1995) to test the effects of these factors on eider nesting success, while controlling results for associated gull nest density. Treatments consisted of (1) high frequency visits (once every 3 days) starting early in the incubation period (HFE), (2) low frequency visits (once every 15 days) starting early in the incubation period (LFE), and (3) high frequency visits starting late in the incubation period (HFL). Analysis of covariance indicated that both disturbance treatments and associated gull nest density had a significant effect on eider nesting success probability. Nesting success probabilities were similar for eiders under HFE and LFE treatments (means=0.317±0.166 [SE] and 0.434±0.172 respectively), indicating that changes in frequency of visits had little impact on nesting success. In contrast, timing of visits had a major influence on nesting success, as the HFL treatment resulted in a significant higher nesting success probability (mean=0.981±0.191) than the HFE treatment. Most nest failures occurred after the first visit in all treatments, although the impact of the first visit was lowest in the HFL treatment. Researchers and wildlife managers should visit eider colonies as late as possible, and avoid visiting colonies associated with high densities of eider egg predators.     

What genetics tell us about the conservation of the critically endangered Balearic Shearwater?

The Balearic shearwater Puffinus mauretanicus is one of the most critically endangered seabirds in the world. The species is endemic to the Balearic archipelago, and conservation concerns are the low number of breeding pairs, the low adult survival, and the possible hybridization with a sibling species, the morphologically smaller Yelkouan shearwater (P. yelkouan). We sampled almost the entire breeding range of the species and analyzed the genetic variation at two mitochondrial DNA regions. No genetic evidence of population decline was found. Despite the observed philopatry, we detected a weak population structure mainly due to connectivity among colonies higher than expected, but also to a Pleistocene demographic expansion. Some colonies showed a high imbalance between immigration and emigration rates, suggesting spatial heterogeneity in patch quality. Genetic evidence of maternal introgression from the sibling species was reinforced, but almost only in a peripheral colony and not followed, at least to date, by the spread of the introgressed mtDNA lineages. Morphometric differences were not correlated with mtDNA haplotypes and introgression is probably due to a secondary contact between the two species several generations ago. Overall, results suggested that the very recent demographic decline in this critically endangered species has not yet decreased its genetic variability, and connectivity found among most colonies should help to reduce species extinction risk. Spreading of introgression should be monitored, but the species is not jeopardized at the moment by genetic factors and the major conservation actions should concentrate at enhancing adult survival.     

Factors affecting bird strikes on aircraft at a coastal airport

I examined the species involved in bird strikes on the runways at J. F. Kennedy International Airport, Long Island, New York from 1973 to 1981. One-hundred-and-forty-two strikes were recorded although 1202 carcasses were found on the runways. Gulls Larus accounted for 47% of the pilot-reported strikes and 70% of the carcasses. Most of the other pilot-reported strikes were shorebirds, small passerines, or were unidentified. During the period 49 species were found as carcasses. Other than gulls, ducks (9%), shorebirds (4%) and owls (3%) were most common. Over half of the gull strikes involved herring Larus argentatus, followed by laughing L. atricilla, ring-billed. L. delawarensis and great black-backed L. marinus gulls. Herring and great black-backed gulls were hit less than expected on the basis of their percent occurrence. Young gulls were hit proportionally more often than expected. Bird strikes and carcass counts were highest in 1975, decreased in 1976 and 1977, increased from 1978 through 1980, and decreased in 1981. For all years pilot-reported strike rates were low (usually less than 1 per 10 000 movements) compared to other airports. Pilot-reported strike rates peaked in May and November during the spring and autumn migration although carcass counts were high from May through December. Over 50% of the pilot-reported gull strikes occurred from 0500–0900 h, although non-gull strikes occurred evenly throughout the day, despite the fact that 70% of plane movements occurred after 1300 h. The pattern of pilot-reported strikes is similar to that reported from Canadian airports.     

The current status and future of Peary Caribou Rangifer tarandus pearyi on the Arctic Islands of Canada

The Peary caribou Rangifer tarandus pearyi is an unique subspecies confined almost entirely to the Canadian Arctic Archipelago. The decline of the population by 89% on the western Queen Elizabeth Islands between 1961 and 1974 has continued until at least 1977. The decline was principally caused by climatic changes but Peary caribou are potentially under additional pressure from hunting and disturbances associated with increasing industrial activities. We believe there are only 10–15,000 Peary caribou in Canada, and the subspieces was classified as ‘Threatened’ in 1979. The population dynamics of Peary caribou are unique among North American ungulates because weather, especially winter weather, dominates not only the reproductive rate but also recruitment and adult survival. The inter-island movements are a significant adaptation not only to sparse ranges and snow conditions, but also to recolonisation of islands that periodically, through a series of severe winters, lose their caribou.     

High levels of habitat loss and fragmentation limit reproductive success by reducing home range size and provisioning rates of Northern saw-whet owls

Studies of the effects of habitat fragmentation have been heavily biased toward population and community questions, with less attention on the effects of habitat loss and fragmentation on individual behaviour and reproduction. We studied the effects of habitat amount and configuration on the foraging behaviour, provisioning rates and physiological condition of breeding male northern saw-whet owls (Aegolius acadicus) nesting in the fragmented aspen parkland of central Alberta, Canada. We then examined the relationship between provisioning behaviour and both reproductive success, and juvenile physiological condition. Males nesting in areas with little forest cover and large inter-patch distances spent more time perching, maintained smaller home ranges, and provisioned their nests less frequently. However, home range size and provisioning rates levelled off in landscapes with moderate to high forest cover. Male owls breeding in areas with low forest cover, and those raising large broods, also exhibited higher levels of chronic stress, as measured by heterophil/lymphocyte (H/L) ratios. Predictably, males that provisioned the nest less often fledged fewer young, which, in turn, exhibited higher variation in physiological condition. These results suggest that low levels of habitat loss and fragmentation may be beneficial to saw-whet owls, potentially by increasing prey abundance. However, high levels of habitat loss and fragmentation appeared to reduce the foraging efficiency of male saw-whet owls, increase their levels of physiological stress, and reduce their reproductive success. Increasing habitat loss and fragmentation may ultimately decrease population sizes of saw whet owls in this area and other species that are similarly affected by changes to in habitat composition or configuration.     

Are edge bird populations doomed to extinction? A retrospective analysis of the common guillemot collapse in Iberia

In the first half of the XXth century, the common guillemot (Uria aalge) was the seabird with the largest breeding population in Atlantic Iberia (ca. 20,000 individuals), the low-latitude limit of the species breeding range. However, this population suffered a dramatic decline and is quasi-extinct at present. The decline was believed to be associated with reduced availability of pelagic prey fish due to climate change. In this study, we analyzed the population change of Iberian guillemots in the second half of the XXth century by means of a retrospective analysis. Our study showed that between 1960 and 1974 the guillemots in Iberia suffered a dramatic population crash (33.3% annual decline) and that subsequently, the population continued to decline at a slower annual rate (13.4%). Simulation models indicated that the factors driving the population crash should be related to adult survival, rather than reproduction. The analysis of environmental and fishery data suggested good climate conditions and higher or sustained availability of pelagic prey fish when the Iberian guillemots crashed. In contrast, relevant human-related factors were affecting adult mortality in that period, specially a rapid and large increase in the number of synthetic fishing nets. During the collapse, no conservation measures were undertaken to mitigate anthropogenic threats and it was assumed, in some extent, that this low-latitude edge population was somehow prone to extinction as a consequence of climate change. This study highlights that to carelessly attribute the decline of rear edge populations to climate change could be highly misleading if the population is suffering from other, particularly human, threats.     

Modelling demography and extinction risk in the endangered Balearic shearwater

Several demographic parameters of Balearic shearwater (Puffinus mauretanicus) were estimated and used to model extinction probabilities for the species, which is an endemic seabird confined to a Mediterranean archipelago. Adult survival was analyzed through capture-recapture models at two colonies free of adult predators during 1997-2002. Extinction probabilities for the world breeding population were modelled using Monte Carlo simulations of population trajectories, introducing stochasticity both demographic and environmental. Adult survival estimate (0.780, SE=0.020, 95% Confidence Intervals: 0.739-0.816) was unusually low for a Procellariiform, suggesting that sources of mortality other than predators (e.g. fishing gears) also occur. A deterministic model showed a declining trend for the world breeding population (λ=0.952), and significantly less than 1. Population viability analysis showed that in the presence of environmental and demographic stochasticities, mean extinction time for the world population was estimated at 40.4 years (SE=0.2), and mean growth rate showed a 7.4% decrease per year. Demographic stochasticity played a more important role than environmental stochasticity in population growth rate.     

Mercury concentrations in fish in a remote Canadian Arctic lake

Lac Ste. Thérèse, a remote Canadian Arctic lake in the Northwest Territories, Canada, has high natural (non-point source) mercury concentrations in fish. The high mercury levels have persisted for over 18 years. Lac Ste. Thérèse has had consistently higher mercury concentration in fish than the other three lakes sampled within the basin, regardless of species tested.