During the four months of summer of 1957 and 1958 the reproductive behaviour and natural history of three sympatric species of cormorants, phalacrocorax auritus, P. pelaqicus, and P. penicillatus, was studied at Mandarte Island, B.C. The three species were found to select different sites for perching and nesting, and to use different habitats for feeding. A description is given of the external colouration of the various age groups of the three species, based in part on banded birds of known ages. It was found that P. auritus and and P. pelagicus are polymorphic prior to breeding and almost monomorphic after the breeding season. No such polymorphism was found in P. penicillatus. The voices of P. auritus, and P. pelagicus include several destinct calls, but P. penicillatus has only one call note. On the other hand only P. penicillatus can flash its gular pouch. The various comfort movements and postures were found to be identical to those of other birds. During locomotion specific differences due to anatomy and habitat adaption became apparant. These differences were further emphasized as species specific signals during social contact. The courtship sequence was found to be functionally identical for all cormorant species studied, but to differ specificly at each step in the sequence, where a signal is used. Except for differences due to size and nesting habitat, the method of incubating the eggs and raising the chicks was found to be identical in P. auritus, and P. pelagicus. It was concluded, that the species specificity of the signals, during courtship and social contact, serves to prevent hybridization, and thus preserves the divergent ecological specialization of the species. This in turn permits a more complete use of the environmental resources. / Science, Faculty of / Zoology, Department of / Graduate

Brood-rearing capabilities and their relation to the problem of clutch-size were investigated in two cormorant species, Phalacrocorax auritus and P. pelagicus, at Mandarte Island, British Columbia. Extra chicks were added to normal sized broods (1 to 4 chicks) so that the range of brood-sizes studied was 1 to 8 in Double-crests (auritus) and 1 to 7 in Pelagics (pelagicus). Fledging success in Double-crests is generally 90 per cent or higher in broods of up to 6 chicks. In Pelagics fledging success drops sharply below 90 per cent in broods greater than 4. In no Pelagic nest did more than 4 chicks fledge, whereas up to 7 chicks fledged in Double-crest nests. Growth rates in both species are lower in supernormal broods. However, this decline amounts to only 12 per cent in Double-crest broods. It is 35 per cent in Pelagic broods. There is a strong relationship between mortality and the low growth rates of certain Pelagic chicks in supernormal broods. Slower growth in large broods is reflected in a fledging period which is longer by several days in both species. The return to Mandarte Island of yearling Double-crests (in 1970) indicates a post-fledging mortality of approximately 50 per cent in normal broods and 47 per cent in supernormal broods, although the latter sample includes only one brood of 7. This slight survivorship difference is not enough to offset the reproductive advantage of large broods. Observation of feeding rates in both species indicates an increase in feeding trips with increasing brood-size which is less than proportional. As this does not appear to be enough to explain the ability of parent Double-crests to feed supernormal broods it was hypothesized that these parents return with more food. Several other aspects of feeding frequency were examined and found consistent with this hypothesis. Study of the success of individual feedings indicated no tendency for a higher success level in normal broods. The strain on parents raising large broods in both species was shown by the decreasing nest-site attendance as broods get larger and as the chicks grow older. The high brood-rearing capabilities of the Double-crests were discussed and two problems on which there was little or no data were raised. It was concluded that Double-crest parents do not endanger their future survivorship in order to raise supernormal broods, although data is poor on this question. A possible breakdown in the feeding of broods greater than 5 may occur under certain conditions. The differing brood-rearing capabilities of the two species were tentatively explained in terms of their population status, i.e., growing versus stable, with the Double-crests the growing population. This idea corresponds with one raised by Lack (1965) who has suggested a correlation between higher than normal brood-rearing capabilities and a growing population. As such, the findings are consistent with Lack's clutch-size hypothesis. The occurrence of most of the nestling mortality in the first two weeks of the nestling period suggest factors other than food may limit brood-rearing success. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (M.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 83-100). Also available in electronic format on the Internet.

No description available.

Thesis (M.S.)--University of Wisconsin--Madison, 1968. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Nevada, Reno, 2008. / "December, 2008." Includes bibliographical references. Online version available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 110-119). Also available on the World Wide Web.

Human wildlife conflicts can represent missed opportunities for ecological monitoring, including tracking invasive species. The great cormorant Phalacrocorax carbo sinensis is the centre such a conflict, where the lack of concrete scientific evidence is often replaced by anecdotal evidence, leading to the vilification of these birds. The primary aim of this study was to assess the extent of the overlap between cormorant diet and the fish the fishermen are allowed to catch on the North West coast of Gotland, the Baltic seas´ biggest island. To assess cormorant diet, the otoliths in the cormorant pellets were analysed. Secondary aims included assessing the potential to use cormorant diet as a proxy for local fish abundances by comparing it to monitoring fisheries in the same area. Highly contentious species only included cod, herring and flounder, none of which were commonly consumed by cormorants. Cormorants and the monitoring fisheries found comparable proportions of all species except for flatfish herring sprat, sculpin. We conclude that the cormorant poses a relatively low risk to the fishing industry on the North Western coast of Gotland and that they could potentially be used as a sentinel for local fish abundances, including tracking invasive species such as the round goby.

Thesis (Ph.D. (Zoology)) -- University of the North, 1996 / Refer to document

Abstract Managing protected areas requires consideration of broad scale social, ecological and in some cases, political factors. Additionally, the impacts of hyperabundant species is often a concern in protected areas as increases in breeding and foraging pressures can alter habitats dramatically. The influences of hyberabundant nesting colonies of waterbird species are well documented. Many studies indicate that waterbird species can influence canopy species as especially on the shoreline of islands, where the most abundant nesting pressures occur. On Lake Erie, Phalacrocorax auritus populations have increased dramatically from a low of 87 nests in 1979 to 16,050 nests in 2007. However, most studies have failed to address the influences that mature tree death may have on the ground layer ecosystem, including increased litter depth, herbaceous species composition and abundance and seed bank composition and viability. Consequently this study sought to quantify the nesting colonies’ influence on coarse woody litter and how nest densities and litter depth influence the herbaceous layer, the seed bank composition and viability across the extent of three Lake Erie islands. My study was designed to quantify the nesting colonies’ influence on these variables across the extent of each island, rather than just the perimeters where the majority of cormorant nests and visible damage exists. I collected my data in the summer of 2008 on East Sister Island, Middle Island and West Sister Island, using plotless-point quarter method, herbaceous layer surveys (incorporating data collected by Parks Canada and Ontario Parks in 2004 and 2007), cormorant nest counts, soil seed bank cores, and litter depth measurements. To test whether there are specific impacts of cormorant nests relegated to the island perimeters versus the rest of the island, an available subset of data on East Sister Island and Middle Island were used. These were expressed as vegetation ‘damage indices’ as classified by Parks Canada and Ontario Parks staff. Kruskal-Wallis tests were used to determine if the different damage indices reveal any influence of cormorant nest density in smaller localized areas as opposed to testing the entirety of the islands. Kruskal-Wallis tests indicated that, island-wide, none of the herbaceous species abundance, diversity (total, native or exotic), seed bank composition, or seed viability has been affected significantly (P > 0.05) by either cormorant nest numbers or large-diameter litter-fall from cormorant nesting activities. However, damage indices (calculated using aerial photography) did indicate that, P .auritus nest density does influence litter depth, herbaceous species abundance and diversity in the island perimeter. Nest density has not significantly affected seed bank abundance or seed viability. My conclusion is that cormorants do not uniformly affect the islands as there is localized damage to the herbaceous layer, restricted primarily to the perimeters of the islands. However, there remains a risk to the interior herbaceous layer of the island if the effects of nesting pressures at the edges advance inward from this perimeter.