WINTERING COMMON POCHARDS (AYTHYA FERINA) AND TUFTED DUCKS (AYTHYA FULIGULA) AT MOORS POOL, UPTON WARREN: DOES STUDY OF THEIR POPULATIONS, HABITAT UTILIZATION AND ACTIVITIES PROVIDE EVIDENCE OF COMPETITION?
My independent study for the Diploma in Ornithology at the University of Birmingham. was intended as an exploratory comparison of the two species and it was planned to observe the two species throughout the period January to April 2001. Unfortunately, the observations had to be curtailed towards the end of February because of the foot and mouth epidemic. Some data collected by the Christopher Cadbury Reserve Management Committee was used to place the 2001 observations in context (John Belsey, 2001, personal communication). The study included a description of the habitat and weather records. Some key aspects are picked out in the following account.
On each visit ten scans of the pool were made, beginning at 5 minute intervals. The presence of birds in different zones of the lake was noted and behaviour was recorded in the following categories: loafing (on land), walking or standing (on land), resting (on water), swimming, swimming with sideways head movements, diving, feeding at the surface, preening (on water), preening (on land) and splashing. The results were analysed statistically, although the fact that observations were only made on eleven occasions made the outcome less satisfactory.
In winter, Common Pochards (hereafter called pochards) and Tufted Ducks (hereafter referred to as tufteds) occur together on Moors Pool. The numbers of the two species fluctuate between years but during January and February records show pochards as more numerous than tufteds. Dearth of invertebrates may explain the relatively low numbers of tufteds in winter (Alan Shepherd, 2001, personal communication). In March tufteds increase and in some years outnumber the pochards. This March increase in tufteds may reflect migratory patterns. In mild winters tufteds begin moving towards their breeding grounds in late February.
During my observations in 2001, tufteds were always less numerous than pochards. Female pochards were more abundant than males. Tufteds were more frequently in open water areas, whereas pochards were commonly in areas with shelving edges.
Among pochards, the behaviour of both sexes varied from day to day, but always most time was spent in loafing and resting, with some swimming and diving. Both sexes were alike. Tufteds were more active than pochards, with a significant difference in behaviour pattern between the sexes. Females were diving more frequently than males.
The study included a detailed discussion of all aspects of the results. Two important aspects are picked out here.
It is recognized that during winter there is usually segregation of the sexes of Common Pochards and other diving ducks, with females tending to move further south, perhaps as a result of competitive exclusion (Cramp, 1977; Owen and Black, 1990; Choudhury and Black, 1991). Unexpectedly, at Moors Pool more females than males were present. This may reflect the quality of the habitat. Larger bodies of water are favoured and males monopolize the best foraging sites. Females may have more success on relatively small bodies of water with plenty of emergent vegetation, as at Moors Pool.
The two species of Aythya can be regarded as members of a single guild, since they are sympatric, forage in similar ways, and overlap in diet and timing of foraging. Despite this overlap, both diet and behaviour patterns differ. Generally, pochards take a higher proportion of plant food and are more active at night. In this diurnal study, pochards were mainly roosting during the day, whereas tufteds were mainly foraging. To the extent that there is temporal segregation between the foraging of the two species, there is some degree of resource partitioning at Moors Pool; the realized niches of the two species differ. Other studies suggest that both species show some degree of flexibility and opportunism and may show different patterns of resource partitioning in other habitats or as the winter progresses (Marsden and Bellamy, 2000; Sekiya et al., 2000). On Moors Pool, Coots Fulica atra to some extent resemble the two species of Aythya in foraging behaviour and also exhibit some kleptoparasitism. This aspect was studied during 2002 by Ian Sutherland for the Certificate of Ornithology.
Although the results of the study on Moors Pool may indicate competition between the two species, an alternative explanation of the results is possible. Common Pochards, male and female Tufted Ducks may be responding independently, rather than competitively, to the conditions in order to optimize their foraging (Begon et al., 1986). Much more study is needed on Moors Pool and elsewhere to clarify the relationship between the two species.
BEGON, M., MARPER, J. L. AND TOWNSEND, C. R. 1986 Ecology: Individuals, Populations and Communities. Oxford: Blackwell.
CHOUDHURY , S. AND BLACK, J. M. 1991 Testing the behavioural dominance and dispersal hypothesis in pochard, Ornis Scandinavica 22: 155-159.
CRAMP, S. (Ed.) 1977 Handbook of the Birds of Europe and the Middle East and North Africa: The Birds of the Western Palaearctic. Volume 1: Ostrich to Ducks. Oxford: Oxford University Press.
MARSDEN, S. J. AND BELLAMY, G.S. 20002 Microhabitat characteristics of feeding sites used by diving duck Aythya wintering on grossly polluted Manchester Ship Canal, UK, Environmental Conservation 27: 278-283. (Abstract.)
OWEN, M. AND BLACK, J. M. (1990) Waterfowl Ecology. Glasgow and London: Blackie.
SEKIYA, Y., HIRATSUKA, J., YAMAMURO, M., OKA, N. AND ABE, M. (2000) Diet selectivity and shift of wintering common pochards and tufted ducks in a eutrophic coastal lagoon, Journal of Marine Systems 26:233-238. (Abstract.)
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