William J. Hamilton

EVOLUTION OF BROOD PARASITISM IN ALTRICIAL BIRDS

habits but also why certain close relatives have not. Brood parasitism has evolved independently a number of times in birds. Best known are the cuckoos, with a complex of Old World species (and three less specialized New World species) highly specialized in the parasitic habit (Friedmann, 1933, 1948). Also, all the African honey guides (Indicatoridae) whose breeding biology is known are brood parasites (Friedmann, 1955). Among passerines brood parasitism has evolved independently in African weaver birds (Ploceidae) and in several species of blackbirds (Icteridae). The only obligate parasite in precocial species is the South American Black-headed Duck (Heteronetta atricapilla), but the North American Redhead (Aythya americana) has populations at various stages of parasitism, from completely independent to complete brood parasitism (Weller, 1959). The independent evolution of brood parasitism in these diverse phyletic lines is clear. But brood parasitism has not necessarily evolved only once in each group. The polyphyletic origin of such a specialized habit within a group might seem quite improbable, but the conditions which might lead to the development of such a habit sug

Social dominance and feeding patterns of spotted hyaenas

Abstract In some parts of East Africa, spotted hyaenas ( Crocuta crocuta ) live in large groups and at high population densities, and scramble competition among clan members during feeding at large carcasses is reported. By contrast, spotted hyaenas in the Namib Desert of southwestern Africa live in small groups and at low densities. When assembled at carcasses, Namib Desert spotted hyaenas show linear dominance hierarchies. Adult females outrank adult males and usually feed one at a time or with their dependent offspring. Feeding rates at small carcasses in the Namib Desert are approximately equal to those reported in East Africa, but at large carcasses Namib Desert spotted hyaenas show linear dominance hierarchies. Adult females outrank adult males and usually feed one at a time or with their dependent offspring. Feeding rates at small carcasses in the Namib Desert are approximately equal to those reported in East Africa, but at large carcasses Namib Desert spotted hyaenas feed significantly more slowly. Thus lower-ranking individuals eventually gain access to large carcasses but are excluded from smaller ones. We relate these patterns of food consumption to possible evolutionary pathways to social hunting by spotted hyaenas.

Radiant Solar Energy and the Function of Black Homeotherm Pigmentation: An Hypothesis

White zebra finches exposed to artificial sunlight used an average of 22.9 percent less energy after they were dyed black. The hypothesis that black homeotherm coloration functions primarily to maximize absorption of radiant solar energy is suggested. This hypothesis may explain the dark skin pigmentation of certain human populations.

Rank and density correlates of inclusive fitness measures in a natural chacma baboon (Papio ursinus) troop

Some demographic characteristics of a group of chacma baboons (Papio ursinus)in a natural environment in northern Botswana were monitored for an 8-year interval. The group size ranged from 73 to 43 individuals. After 3 years at a high density, the group size declined over a 2-year interval, then stabilized again at reduced numbers (−41 %) and biomass (−40%) for over 2 years. The reduction in group size and biomass was followed by an increase in fecundity, greater for high-ranking than for low-ranking females. At the larger group size, survival was lower for infants born to low-ranking than to high-ranking females. Infant survival rates by female rank were equal at the lower density. The mean weight of adult females increased as the density decreased, but there was no correlation between female rank and body mass. We conclude that there is a negative relationship of density to individual condition and reproductive success and that there are fitness advantages to high female rank.

Environmental determinants of object manipulation by chacma baboons (Papio ursinus) in two southern African environments

Expressions of object manipulation activities by chacma baboons, Papio ursinus, are related to environmental conditions. Three baboon troops living in a desert river ravine share more object manipulation behavior patterns among themselves than they do with two troops living in a swampy environment. The basis of all differences, between troops and between populations of troops, may be based upon environmental differences. Economic conditions prevailing for each troop depend not only upon the availability of a resource exploited by a particular behavior pattern but also upon the availability and need to utilize alternative resources. The repertoire of social object manipulation activities is greater in the swamp environment where troops are larger, there is greater social mobility, and the number of potential social interactions is greater. Certain object manipulation activities were seen only once or a few times. Such observations show that more object manipulation activities are available than those which are routinely expressed. When such behavior patterns are rewarded they are probably incorporated into the object manipulation repertoire.

Natal male baboon rank rises and successful challenges to resident alpha males

SummaryAfter an interval (X = 6 months), high ranking male chacma baboons (Papio cynocephalus ursinus) lose their status to immigrants. Attainment of alpha rank by immigrants is a qualitatively different process from thestepwise increase in status noted in linear dominance hierarchies. The departing rank of natal emigrants was 5.4, while the first measured rank, shortly after transfer into a new troop, was 1.5. Abrupt rises to alpha rank involve direct challenges to the current alpha male. Fourteen of 19 prime immigrants attained alpha rank at first transfer. Rank rises may result if individuals forego contests, retaining lower hierarchical positions in their natal troop to avoid the costs of conflict prior to natal emigration. In this population some males do breed in their natal troops without differing from immigrants in their reprodocutive success. Five males that rose to high rank within their natal troops also made rapid rank rises to the top of the hierarchy. Withholding of aggressive efforts in natal troops to avoid inbreeding thus is not an adequate explanation of the rank rises we observe in this population. The high probability of successful challenges can be explained by assuming an asymmetry in costs of losing (resource value) to tenured alpha males or a greater fighting ability of challengers.

Demographic consequences of a food and water shortage to desert Chacma Baboons, Papio ursinus

The age-sex composition of a chacma baboon (Papio ursinus)population changed following a 5-month interval of extreme food and water shortages. Mortality was significantly greater among adult females, juveniles, and infants than among adult males. The probable basis of 19 of 22 deaths during the interval of food and water shortage was starvation caused by drought conditions which localized water sources, reducing access to food resources. This resulted in a long-term (> 6-year) shift in adult sex ratios within this three-troop population, from 1.04 to 1.42-1.58 adult and subadult males per adult female. Patterns of intertroop interaction were also influenced by food scarcity, which determined which troop was most seriously affected.

Chacma Baboon Tactics during Intertroop Encounters

Intertroop conflicts occur regularly in populations of chacma baboons ( Papio ursinus ) in a desert canyon in the Namib Desert of South West Africa and in the Okavango Swamps of Botswana. These interactions range from peaceful mingling of juveniles to violent chases by adult males. Encounters may involve face-offs, coordinated group charges into the ranks of the opposing troop, intratroop herding by adult males, and vocalizations. Encounters between the desert canyon troops vary for the same troop, depending upon the alien troop encountered. In the desert, intertroop dominance was correlated with large troop size and the number of large males per troop. In the swamp, where neighboring troops shared more stable troop boundaries, intertroop interactions were more frequent and their character less variable. Adult females generally withdraw or are chased from encounter sites. When troops come together juveniles may initiate play or groom members of alien troops. Male baboons dominate intertroop encounters and are hostile in their interactions.

Inbreeding and reproductive success in a natural chacma baboon, Papio cynocephalus ursinus, population

Abstract Six of 19 male chacma baboons living in a natural environment in Botswana were born in troops where they attained alpha status. At least three of these six males sired young in their natal troops. Nine other paternal males were immigrants, hence they were more distantly related to their mates, who were all natal. Offspring of natal and immigrant parents survived equally well to 90 days. These observations suggest that for this and other mammalian species the evolutionary history of a population may determine inbreeding costs.

Starling Dispersal From a Winter Roost

Starling roosting behavior is considered in terms of resource acquisition. Our hypothesis is that dispersing starlings behave to maximize the efficiency and rate of energy gain. This hypothesis can explain of the winter starling roosting behavior. The value of strategies pursued by individuals within the system depends upon the size of the population utilizing a roost. As the roost population grows, more distant resources are utilized. At maximum roost populations individuals may disperse daily as much as 50 miles from the roost. During dispersal most individuals make in—transit stops to feed. These stops may provide information about the potentially more lucrative energy reserves nearer the roost, reducing the distance flown when they are favorable. Flocking actions probably make resource evaluation more efficient because the experience of the members of a group will provide more reliable information about the values of a resource field than an individuals personal experience. Linear dispersal directly away from roots is assumed to be maximally advantageous. This is because intraspecific competition declines with distance from the roost, and flight is costly of energy. On foggy, and overcast mornings dispersing starlings do not extend as far from the roost, and the flight is less accurately oriented. This suggest a relatively high adaptive value for accurate orientation mechanisms in this socio—economic system. Dispersing flocks are larger during overcast, supporting the hypothesis that group processes in orientation enhance orientation accuracy.