Matti Åhlund

Female ducks can double their reproduction

By engaging in extra-pair matings, the most successful males in some bird species can father twice as many young as are present in their own nest. Here we describe a female parallel in goldeneye ducks (Bucephala clangula), whereby some females can double their reproductive output by combining brood parasitism with normal nesting. This huge reproductive advantage should create strong selection for parasitic tactics.

Brood parasitism: Female ducks can double their reproduction

By engaging in extra-pair matings, the most successful males in some bird species can father twice as many young as are present in their own nest. Here we describe a female parallel in goldeneye ducks (Bucephala clangula), whereby some females can double their reproductive output by combining brood parasitism with normal nesting. This huge reproductive advantage should create strong selection for parasitic tactics.

Gull predation on eider ducklings Somateria mollissima: effects of human disturbance

Abstract Gull predation on eider ducklings Somateria mollissima in an archipelago on the Swedish west coast is described. Both gull encounter rate and gull predation rate were 200–300 times higher on creches disturbed by boats than on undisturbed creches. Encounter rates increased with the proximity of the creche to breeding sites of gulls and to passing boats. Repeated disturbances further raised gull encounter rates. Near islands with nesting gulls, intense boating activity may severely affect fledgeling production among ducks. Our results suggest that boating should be restricted in important duckling rearing areas.

Are indices reliable for assessing conservation value of natural areas? An avian case study

Abstract Bird censuses in two wetland habitats (bogs and wet meadows) in SW Sweden were used to test the applicability of five conservation indices suggested for birds. The censused sites were first evaluated and ranked by the authors, then ranked according to each of the indices. Two indices based on species diversity (H′ or Λ) showed a poor agreement with our evaluation; we suggest that they should not be used for ranking of sites of ornithological interest. Three indices based on rarity showed a better agreement with our evaluation, but were influenced by the size of the geographical area for which rarity was assessed. None of the five indices takes into account all of the relevant aspects for an evaluation of the bird fauna at the different sites. Before constructing further indices, conservationists must reach agreement on which evaluation criteria to use, and how to use them. It may, however, not be feasible to construct a single index; a better strategy might be to construct indices only for single evaluation criteria.

Behavioural tactics at nest visits differ between parasites and hosts in a brood-parasitic duck

Whether conspecific brood parasitism is adaptive is a matter of debate. It may just be accidental when suitable nest sites are scarce. I tested this and other hypotheses, using video recordings and quantitative behavioural observations at nestboxes of individually marked common goldeneyes, Bucephala clangula . In 11 of 13 parasitized nests filmed, parasite behaviour differed markedly from that of hosts during most of the egg-laying sequence. Hosts typically started and laid the most eggs in the nest, covered the clutch when leaving it, and deposited down. Parasites covered the eggs poorly and did not deposit down. Hosts spent increasing time on the nest over the laying sequence, whereas parasites did not. Parasites tended to lay eggs later than hosts in the morning, possibly in response to nest guarding by hosts. When in the nest, hosts usually prevented females from entering, but parasites rarely did so. Of 84 parasitic eggs, 85% were laid by ‘true parasites’, and 15% by females that behaved like hosts but were eventually displaced by another female. Most (73%) of the ‘truly’ parasitic eggs were from females that were marked as adults previously, and 27% from new recruits. Parasitism in this goldeneye population is thus usually an alternative behavioural tactic, distinctly different from the behaviour of hosts, and not simply a side-effect of competition between females over the same nest.

Don't put all your eggs in one nest: spread them and cut time at risk.

In many egg-laying animals, some females spread their clutch among several nests. The fitness effects of this reproductive tactic are obscure. Using mathematical modeling and field observations, we analyze an unexplored benefit of egg spreading in brood parasitic and other breeding systems: reduced time at risk for offspring. If a clutch takes many days to lay until incubation and embryo development starts after the last egg, by spreading her eggs a parasitic female can reduce offspring time in the vulnerable nest at risk of predation or other destruction. The model suggests that she can achieve much of this benefit by spreading her eggs among a few nests, even if her total clutch is large. Field data from goldeneye ducks Bucephala clangula show that egg spreading enables a fecund female to lay a clutch that is much larger than average without increasing offspring time at risk in a nest. This advantage increases with female condition (fecundity) and can markedly raise female reproductive success. These results help explain the puzzle of nesting parasites in some precocial birds, which lay eggs in the nests of other females before laying eggs in their own nest. Risk reduction by egg spreading may also play a role in the evolution of other breeding systems and taxa—for instance, polyandry with male parental care in some birds and fishes.

Brood parasitism, relatedness and sociality: a kinship role in female reproductive tactics: Brood parasitism and kinship

Conspecific brood parasitism (CBP) is a reproductive tactic in which parasitic females lay eggs in nests of other females of the same species that then raise the joint brood. Parasites benefit by increased reproduction, without costs of parental care for the parasitic eggs. CBP occurs in many egg‐laying animals, among birds most often in species with large clutches and self‐feeding young: two major factors facilitating successful parasitism. CBP is particularly common in waterfowl (Anatidae), a group with female‐biased natal philopatry and locally related females. Theory suggests that relatedness between host and parasite can lead to inclusive fitness benefits for both, but if host costs are high, parasites should instead target unrelated females. Pairwise relatedness (r) in host–parasite (h‐p) pairs of females has been estimated using molecular genetic methods in seven waterfowl (10 studies). In many h‐p pairs, the two females were unrelated (with low r, near the local population mean). However, close relatives (r = 0.5) were over‐represented in h‐p pairs, which in all 10 studies had higher mean relatedness than other females. In one species where this was studied, h‐p relatedness was higher than between nesting close neighbours, and hosts parasitized by non‐relatives aggressively rejected other females. In another species, birth nest‐mates (mother–daughters, sisters) associated in the breeding area as adults, and became h‐p pairs more often than expected by chance. These and other results point to recognition of birth nest‐mates and perhaps other close relatives. For small to medium host clutch sizes, addition of a few parasitic eggs need not reduce host offspring success. Estimates in two species suggest that hosts can then gain inclusive fitness if parasitized by relatives. Other evidence of female cooperation is incubation by old eider Somateria mollissima females of clutches laid by their relatives, and merging and joint care of broods of young. Merging females tended to be more closely related. Eiders associate with kin in many situations, and in some geese and swans, related females may associate over many years. Recent genetic evidence shows that also New World quails (Odontophoridae) have female‐biased natal philopatry, CBP and brood merging, inviting further study and comparison with waterfowl. Kin‐related parasitism also occurs in some insects, with revealing parallels and differences compared to birds. In hemipteran bugs, receiving extra eggs is beneficial for hosts by diluting offspring predation. In eggplant lace bugs Gargaphia solani, host and parasite are closely related, and kin selection favours egg donation to related females. Further studies of kinship in CBP, brood merging and other contexts can test if some of these species are socially more advanced than presently known.

Female ducks can double their reproduction: Brood parasitism

By engaging in extra-pair matings, the most successful males in some bird species can father twice as many young as are present in their own nest. Here we describe a female parallel in goldeneye ducks (Bucephala clangula), whereby some females can double their reproductive output by combining brood parasitism with normal nesting. This huge reproductive advantage should create strong selection for parasitic tactics.