The ecological factors underlying the evolution of helping behavior in birds and mammals are examined. I argue that a necessary first step for cooperative breeding is substructuring population into small, stable, social units; most known cases these extended-family units. conditions leading to development such units explored, general model presented emphasizes constraints limit possibility personal, independent breeding. When severe occur, selection will favor delayed dispersal continued...

The technique described in this paper eliminates the necessity of prolonged direct observation and bypasses problem expensive cumbersome equipment. It thus provides a means obtaining simultaneous records on moderately large samples birds. To date has been tested over 1,000 times both field planetaria. authors wish to thank Helmut Mueller for assisting with tests, Harrison B. Tordoff commenting upon manuscript. TECHNIQUE

Abstract During the summers of I967 I968 and I969, I studied acoustical communication system Indigo Bunting (Passerina cyanea) by means playback experiments. Attention was directed to deciphering those properties territorial song used in species identification. tested importance different parameters exposing birds recordings normal artificially modified vocalizations. The level agonistic response exhibited male territory holders as a bioassay effectiveness experimental allowing recognition....

Three groups of indigo buntings were hand-raised in various conditions visual isolation from celestial cues. When they had been prevented viewing the night sky prior to autumn migration season, birds tested under planetarium skies unable select normal direction. By contrast, when exposed as juveniles a normal, rotating, sky, individuals displayed typical southerly directional preferences. The third group was an incorrect which stars rotated about fictitious axis. during autumn, these took up...

Optimal skew models explain reproductive sharing within social groups as resulting from incentives given by controlling dominants to subordinates in return for peaceful cooperation. We explore two versions of an alternative, the incomplete control model, evolution groups. In this have only limited over allocation reproduction and must expend effort increase their share total group output show that, when relatedness between dominant subordinate is symmetrical, (1) subordinate's fraction...

Abstract White‐fronted bee‐eaters are colonially breeding birds that exhibit highly developed helping‐at‐the‐nest. Through long‐term studies of an individually‐marked population, we have documented two costs social living: 1) harassment mated females by extra‐pair males, and 2) intra‐specific parasitism who lay eggs in the nests others. Breeding sexually chased and, occasionally, forceably males other than their mates. Focal‐sampling throughout period receptivity revealed average female is...

This study tested two hypotheses concerning the cognitive processes underlying human mate choice in Western society: ( i ) preference is conditional that selectivity of individuals' based on their perception themselves as long-term partners, and ii decision rule governing such translating oneself a given attribute into comparable for same mate. Both were supported. A two-part questionnaire was completed by 978 heterosexual residents Ithaca, New York, aged 18–24; they first rated importance...

Among many cooperatively breeding birds and mammals, grown offspring remain with their parents aid them in rearing successive broods/litters of young. Through such actions, helpers can be said to "repay" part the cost production. When a strong sexual asymmetry exists preponderance philopatry helping behavior, selection should favor females that skew sex ratio sex. We expand Fisher's sex-ratio model incorporate concept sex-specific helper payback. The result is an imbalance evolutionarily...

In part I (Emlen 1982), an ecological constraints model was developed to predict the circumstances under which grown offspring would remain in familial units with their parents. Such retention considered a necessary, but not sufficient, condition for evolution of helping behavior. Whether or nonbreeding auxiliaries will participate as helpers such groups depend upon costs and benefits helping, measured from viewpoints both breeder helper. this paper, these are formalized, conclusion is...

Bank swallows nest gregariously in colonies usually ranging from 10 to 300 nests. Different pairs within the same colony are highly synchronized with each other, and 67 percent of nests fledged their young over a period only 6 days. This high degree synchronization is demonstrated be adaptive significance. Reproductive fitness increases as function precision synchrony colony. It proposed that social foraging plays an important role maximizing feeding efficiency this species asynchronous...

Ecology is a fundamental driving force for the evolutionary transition from solitary living to breeding cooperatively in groups. However, fact that both benign and harsh, as well stable fluctuating, environments can favour evolution of cooperative behaviour constitutes paradox environmental quality sociality. Here, we propose new model - dual benefits framework resolving this paradox. Our distinguishes between two categories grouping resource defence derive group-defended critical resources...

IN Part I of this publication (Emlen, 1967), discussed the Zugunruhe orientation exhibited by caged migratory Indigo Buntings, Passerina cyanea. The majority experimental birds consistently demonstrated an ability to select appropriate migration direction when tested under natural or artificial (planetarium) night skies. These results, in conjunction with predictable behavioral changes manipulated planetarium skies led me hypothesize that celestial cues provided at least one means enabling...

SUMMARY (1) Among white-fronted bee-eaters (Merops bullockoides) near Nakuru, Kenya, helpers dramatically increased the fitness of breeders. Using 5 years data, we examine relative importance food availability, breeder attributes and group size on reproductive success. (2) Both availability attending nest had significant effects productivity, while characteristics breeders (age, experience) did not. Helpers their effect almost entirely through productivity per nesting attempt, each helper...