Parental and embryonic behaviours in precocial birds
Sammanfattning: This thesis deals with behaviours during reproduction in precocial birds, both from the perspective of the female and of the embryos. Female pheasants in good physical condition laid larger eggs and produced a higher proportion of daughters than females in poor condition. Furthermore, females mated with a male with long spurs produced a higher proportion of sons, showing that females adjusted the primary sex ratio in relation to the phenotypic quality of the male. Females in good physical condition spent longer time on the nest both during the egg-laying and incubation period and tended to make more incubation recesses per day. This increased activity around the nest increased the risk of nest predation. Females often continued to lay eggs after the start of full-time incubation. The number of eggs laid during incubation was positively related to the number of nesting attempts made by the female the same season, suggesting that she may start incubation early to reduce the risk of nest predation. Embryos of precocial birds must hatch synchronously to be able to leave the nest together with the female shortly after hatching. The synchronization of hatching can be achieved either by shortening or prolonging the incubation period of the late or early embryos, respectively. Our experiments showed that mallard ducks were more inclined to shorten their incubation period, while pheasants were better at delaying hatching. Measurements of the oxygen consumption of embryos during incubation showed that embryos that were stimulated to hatch early had a higher oxygen consumption rate during the last days before external pipping, and did not have a distinct plateau phase like embryos hatching after a normal incubation period have. This indicates that embryos that shorten their incubation period try to compensate for the lost incubation time by accelerating their development during the last days of incubation. The reduction of the incubation length had several disadvantages for the chicks after hatching. Both pheasant and mallard embryos that accelerated their development was smaller after hatching, and in mallards the growth rates of body mass, tarsus and wing length were lower. Embryos of both species had a better sence of balance and ability to walk immediately after hatching if they delayed hatching, in addition to reduced rate of mortality.
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