Elmberg, J. 2003: Density-dependent breeding success in mallards Anas platyrhynchos on a eutrophic lake. - Wildl. Biol. 9: 67-73.
Census data from a eutrophic lake collected in 1987-1999 were used to study nesting and breeding success in mallards Anas platyrhynchos. In each year there were 6-19 pair counts and 13-34 brood counts. The maximum combined count of single males and pairs (i.e. on any day in any of three census periods in May) provided the best fit with subsequent estimates of breeding success. Nesting success (average brood:pair ratio = 0.52), brood size of older ducklings (mean = 5.7) as well as fledgling success (2.86 juveniles per nesting pair) were higher than in many previous mallard studies. Per capita brood production as well as per capita fledgling production was negatively density dependent, but the latter was not statistically independent of the former. There was no correlation between per capita fledgling success and duckling mortality on a year-by-year basis, hence the density-dependent pattern in breeding success appears to be mediated through variation in nesting success. The number of paired females at the start of the breeding season correlated positively with the production of fledged juveniles the year before.
Key words: Anas platyrhynchos, breeding success, density-dependence, mallard, population regulation
Johan Elmberg, Department of Mathematics and Natural Sciences, Kristianstad
University, SE-291 88 Kristianstad, Sweden - e-mail: Johan.Elmberg@mna.hkr.se
Received 22 February 2002, accepted 13 June 2002
Associate Editor: Hannu Pöysä