pre-hatch brood amalgamation, whereby a female lays her eggs in the nest of another female and the recipient thereafter provides all further care of the eggs and resulting offspring, and (ii) post-hatch brood amalgamation, whereby a female abandons or loses her young to another female after hatch, and the recipient subsequently tends the foster young. Some authors have viewed these behaviours as accidental or aberrant and of little evolutionary significance. More recently, a number of alternative hypotheses have been suggested. However, few of these hypotheses have been contrasted as viable alternatives and tested in the field, largely because an appropriate theoretical framework is lacking. We analyze the frequency of occurrence of brood amalgamation in North American anatids. We also review the hypotheses that have been proposed to explain these behaviours and erect a theoretical framework which applies to the evolution of both pre-hatch and post-hatch brood amalgamation, and which may apply to species other than those of the Anatidae. Finally, we show that the occurrence of brood amalgamation in North American waterfowl may be associated with low relative resource availability and K-type life-history traits. EADIE, J. McA., KEHOE, F. P., et NUDDS, T. D. 1988. Pre-hatch and post-hatch brood amalgamation in North American Anatidae: a review of hypotheses. Can. J. Zool. 66 : 1709 -172 1. Deux formes de fusion de couvCes se produisent frCquemment chez plusieurs espkces d'oiseaux de rivage nord-amCricains : ( i ) fusion des couvCes avant 1'Cclosion : certaines femelles pondent leurs oeufs dans le nid d'une autre femelle et la femelle rCcipiendaire donne alors tous les soins aux oeufs et aux oisillons qui en rCsultent et (ii) fusion des couvCes aprks 1'Cclosion :certaines femelles abandonnent leurs oisillons a une autre femelle ou les perdent aprks 1'Cclosion et la femelle rkcipiendaire assure alors les soins aux petits qu'elle adopte. Certains auteurs considkrent ces comportements comme accidentels ou aberrants et de peu d'importance Cvolutive. Plus rCcemment, d'autres hypothkses ont Ct C proposCes, mais peu ont Ct C retenues ou CprouvCes en nature, en grande partie parce qu'elles ne sont reliCes a aucun cadre thCorique appropriC. On trouvera ici une analyse de la frCquence de fusion des couvCes chez les Anatidae nord-amkricains, de meme qu'une rCvision des hypothkses proposCes pour expliquer ces comportements; cette rCvision nous permet d'Ctablir un cadre thCorique qui peut s'appliquer a 1'Cvolution de la fusion prC-Cclosion et de la fusion post-Cclosion des couvCes et qui peut convenir aussi a des espkces autres que les Anatidae. I1 est possible que la fusion des couvCes chez la sauvagine nord-amCricaine soit associCe a une disponibilitk relative faible des ressources et a des caractkristiques d'une stratCgie dkmographique de type K.[Traduit par la revue]

We studied the effects of dietary fiber, of plant versus animal diets, and of diet diversity on the digestive organ morphology of captive Mallards (Anas platyrhynchos). Four experimental diets were used: whole corn (low fiber, plant), trout chow (low fiber, primarily animal), rabbit chow (high fiber, plant), and a diverse diet consisting of each of the preceding diets fed daily in random order. Every 5 days for 25 days, we sampled birds from each diet group (N = 6–8) and weighed each bird and its abdominal fat, gizzard, ceca, small intestine, and liver, and then measured its ceca and small intestine length. Other than differences explained by their different body sizes, the sex of the birds had no effect on gut measurements. Changes in body weight and abdominal fat weight suggested that Mallards existed equally well on each of the four diets, presumably because changes in their digestive organs allowed them to have similar digestive efficiencies when eating different diets. Birds on the high fiber diet had the largest digestive organs, but birds on all diets showed changes in digestive organs. The diverse diet produced effects on digestive organ morphology similar to those of the two low-fibre diets. Except for a larger gizzard for macerating corn in birds on that diet, there was no difference in the digestive organs between birds eating animal foods and those eating low fiber plant foods. The maximum weight of gizzard, intestine, and ceca of birds on the high fiber diet was reached in 10 days. However, ceca and intestine lengths of these birds were still increasing after 25 days. This observation suggests that birds can continue to respond to a change in diet after limits to the mass of their digestive organs have been reached.

Ceca length, small intestine length, and gizzard weight were measured for individuals of five species of diving ducks collected at Long Point Bay, Lake Erie, and Mitchell's Bay, Lake St. Clair, Ontario, in the falls of 1982 and 1983. The five species were Lesser Scaup (Aythya affinis, N = 84), Ring-necked Duck (Aythya collaris, N = 57), Greater Scaup (Aythya marila, N = 54), Redhead (Aythya americana, N = 58), and Canvasback (Aythya valisineria, N = 112). The diets of these species reportedly differ in diversity as well as in amount of fibre, and interspecific differences in gut morphology, not explained by differences in body weight, were accounted for by general differences in diet. Canvasbacks, although the heaviest species, had the shortest ceca, short intestines and light gizzards, presumably because their diet contains the least fibre. Conversely, the relatively small-bodied scaup species had the longest small intestines, likely because of their diverse diets which include animal and plant material. Our results show that morphological differences in waterfowl guts reflect dietary differences at a particular time and location and also illustrate the importance of adjusting gut measurements to body weight before making interspecific comparisons.

No abstract

I tested several hypotheses regarding the adaptive significance of crèching behaviour using white-winged scoters (Melanitta fusca delgnadi) at Redberry Lake, Saskatchewan. Scoter crèches consist of a single female tending the young of one or more conspecifics. There was no relationship between a female's weight at the end of incubation and whether she stayed with ducklings. Therefore, there is no evidence that females in poor condition abandon their young more frequently than other females. No relationship was found between a female's age and her association with ducklings. Therefore, crèching does not appear to be related to female age or experience. Observations of color-marked ducklings in 1985 showed that 7 out of 10 females tended crèches that were composed entirely of fostered young. The survival of ducklings from large groups was greater than that from small groups, so crèching does not appear to be a strategy that enhances individual fitness of crèche-tending females. However, because of the high degree of philopatry displayed by female scoters, crèching could enhance inclusive fitness if crèches contain the young of related individuals. This hypothesis could not be tested.