Hemosporidian blood parasites in seabirds—a comparative genetic study of species from Antarctic to tropical habitats

Whereas some bird species are heavily affected by blood parasites in the wild, others reportedly are not. Seabirds, in particular, are often free from blood parasites, even in the presence of potential vectors. By means of polymerase chain reaction, we amplified a DNA fragment from the cytochrome b gene to detect parasites of the genera Plasmodium, Leucocytozoon, and Haemoproteus in 14 seabird species, ranging from Antarctica to the tropical Indian Ocean. We did not detect parasites in 11 of these species, including one Antarctic, four subantarctic, two temperate, and four tropical species. On the other hand, two subantarctic species, thin-billed prions Pachyptila belcheri and dolphin gulls Larus scoresbii, were found infected. One of 28 thin-billed prions had a Plasmodium infection whose DNA sequence was identical to lineage P22 of Plasmodium relictum, and one of 20 dolphin gulls was infected with a Haemoproteus lineage which appears phylogenetically clustered with parasites species isolated from passeriform birds such as Haemoproteus lanii, Haemoproteus magnus, Haemoproteus fringillae, Haemoproteus sylvae, Haemoproteus payevskyi, and Haemoproteus belopolskyi. In addition, we found a high parasite prevalence in a single tropical species, the Christmas Island frigatebird Fregata andrewsi, where 56% of sampled adults were infected with Haemoproteus. The latter formed a monophyletic group that includes a Haemoproteus line from Eastern Asian black-tailed gulls Larus crassirostris. Our results are in agreement with those showing that (a) seabirds are poor in hemosporidians and (b) latitude could be a determining factor to predict the presence of hemosporidians in birds. However, further studies should explore the relative importance of extrinsic and intrinsic factors on parasite prevalence, in particular using phylogenetically controlled comparative analyses, systematic sampling and screening of vectors, and within-species comparisons

Application of habitat suitability modelling to tracking data of marine animals as a means of analyszing their feeding habitats

This paper investigates the potential for using quantitative applications of statistical models of habitat suitability based on marine animal tracking data to identify key feeding areas. Presence-only models like Ecological Niche Factor Analysis (ENFA) may be applicable to resolve habitat gradients and potentially project habitat characteristics of tracked animals over large areas of ocean. We tested ENFA on tracking data of the northern gannet (Morus bassanus) obtained from the colony at Bass Rock, western North Sea in 2003. A total of 217 diving events were selected for model development. The ecological variables of the model were calibrated by using oceanographic structures with documented influences on seabird distribution, derived from satellite and bathymetric data. The model parameters were estimates of habitat marginality and specialisation computed by comparing the distribution of the gannet in the multivariate oceanographic space encompassed by the recorded logger data with the whole set of cells in the study area. Marginality was identified by differences to the global mean and specialization was identified by the ratio of species variance to global variance. A habitat suitability index was computed on the basis of the marginality factors and the first four specialisation factors by allocating values to all grid cells in the study area, which were proportional to the distance between their position and the position of the species optimum in the factorial space. Although gannets were using a large sector of the North Sea for feeding, ENFA estimated high habitat suitability scores within a relatively small coherent zone corresponding to a hydrographic frontal area, located east of the colony. The model was evaluated by using Jack-knife cross-validation and by comparison of the predicted core feeding area with results from historic field surveys. We discuss the limitations and potentials for applying habitat suitability models to tracking data in the marine environment, and conclude that the inclusion of hydrodynamic variables seems to be the biggest constraint. Overcoming this constraint, ENFA provides a promising method for achieving improved models of the distribution of marine species with high research and conservation priority. Due to the better coverage of entire feeding ranges, the limited influence of historic factors and the lack of bias from sampling design, marine animal tracking may provide better data than at-sea surveys for habitat suitability modelling

Sex-Specific Habitat Utilization and Differential Breeding Investments in Christmas Island Frigatebirds throughout the Breeding Cycle.

In seabirds, equal bi-parental care is the rule, as it is considered crucial for raising chicks successfully because seabirds forage in an environment with unpredictable and highly variable food supply. Frigatebirds forage in poor tropical waters, yet males reduce and even stop parental care soon after chick brooding, leaving the female to provision the chick alone for an extended fledging period. Using bird-borne tracking devices, male and female Christmas Island Frigatebirds (Fregata andrewsi) were investigated during the brooding, late chick rearing and post-fledging period to examine whether sexes exhibit foraging strategies that may be linked to differential breeding investments. During brooding, males and females showed similar foraging behaviour under average marine productivity of oceanic waters close to the colony, but males shifted to more distant and more productive habitats when conditions deteriorated to continue with reduced chick provisioning. During the late chick rearing period, females progressively increased their foraging range to the more distant but productive marine areas that only males had visited during brooding. Birds spent the non-breeding period roosting in highly productive waters of the Sunda Shelf. The sex-specific utilisation of three different foraging habitats with different primary productivity (oceanic, coastal, and shelf areas) allowed for temporal and spatial segregation in the exploitation of favourable habitats which seems to enable each sex to optimise its foraging profitability. In addition, post-fledging foraging movements of females suggest a biennial breeding cycle, while limited information on males suggests the possibility of an annual breeding cycle

Resource partitioning between incubating and chick-rearing brown boobies and red-tailed tropicbirds on Christmas Island

Background: In oligotrophic tropical marine environments, the main mechanism explaining the coexistence of sympatric seabirds is segregation by habitat or segregation by prey within the same habitat. Both types of segregation can play a role during the breeding season due to different constraints associated with different phases of the breeding cycle. By using stable isotope analyses, we investigated intra- and interspecific foraging segregation in two tropical seabird species, the red-tailed tropicbird Phaeton rubricauda and the brown booby Sula leucogaster, breeding sympatrically on Christmas Island, Indian Ocean. We compared isotopic values of delta C-13 and delta N-15 in blood from incubating and chick-rearing adults of both species. Results: The results showed small but significantly interspecific and intraspecific differences in delta C-13 and delta N-15 values. Differences in delta C-13 values suggest spatial segregation in the main foraging grounds between the two species during the breeding season as well as between incubating and chick-rearing brown boobies. In contrast, red-tailed tropicbirds probably exploited similar foraging habitats during both breeding stages. delta N-15 values did not indicate diet-related differences, neither within nor between species, suggesting a highly opportunistic feeding behavior to cope with the limited prey available in the oligotrophic marine environment. Conclusions: Competition for prey in breeding red-tailed tropicbirds and brown boobies seems to be reduced by spatial segregation enabling both species to successfully reproduce in sympatry in an oligotrophic tropical marine environment

Details of satellite transmitter deployments on Christmas Island Frigatebirds covering the late chick rearing and post-breeding periods (F = female, M = male).

<p>Details of satellite transmitter deployments on Christmas Island Frigatebirds covering the late chick rearing and post-breeding periods (F = female, M = male).</p

Migration and foraging movements during the post-breeding period.

<p>Tracks of Christmas Island Frigatebirds during the post-breeding period determined by satellite telemetry (females = red lines, male = blue line, roosts = black dots, arrows indicate travel direction). The dashed box delineates the “Sunda Shelf area” for which the chlorophyll <i>a</i> data was compiled (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129437#sec002" target="_blank">methods</a>).</p

Foraging movements during the brooding period.

<p>Foraging tracks of Christmas Island Frigatebirds during the brooding periods of (a) 2009 and (b) 2010 determined by GPS-loggers and satellite transmitters (female tracks = red, male tracks = blue; thin black line = 200 m isobath).</p

Core foraging areas and chlorophyll <i>a</i> concentrations during the brooding period.

<p>Core foraging area (50% Kernel density estimation) of Christmas Island Frigatebirds and chlorophyll <i>a</i> concentrations during the brooding periods of (a) 2009 and (b) 2010 (females = solid line, males = dashed line; chlorophyll <i>a</i> concentration for May and June combined, logarithmic scale).</p

Foraging movements during the late chick rearing period.

<p>Tracks of foraging trips of female Christmas Island Frigatebirds during the late chick rearing period determined by satellite telemetry. The solid box delineates the “CI waters area” and the dashed box delineates the “Java Head and South Coast area” for which the chlorophyll <i>a</i> data was compiled (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129437#sec002" target="_blank">methods</a>).</p