Physical and Behavioral Factors in Sociality and Evolution of Certain Parrots (Aratinga)

THE concepts of species-specific characteristics and social releasers as developed by ethologists (see Tinbergen, 1951; 1959: 318-330) have intrigued animal behaviorists as much as any concept in the science of ethology. Utilizing these concepts, I have been engaged since 1959 in studies of the behavior of parakeets of the genus Aratinga, primarily A. c. canicularis, the Orange-fronted Parakeet, and also recently other forms. The acquisition, in 1960, of captive birds of A. c. eburnirostrum and, in 1962, of 12 Aratinga astec, the Aztec Parakeet, made possible experiments and observations on the function of morphological and behavioral characteristics which are involved in sociality. The results of these studies have bearing upon our understanding of psittacid evolution. Elsewhere (1963) I have described the epigamic and reproductive biology and (1965) the flock social behavior of A. canicularis. This parakeet is highly social in the wild except during the nesting season, when pairs disperse to nest. Flocks of 5 to 50 birds are otherwise common throughout the species' range, and groups of up to 12 or 15 birds typically wander about between scattered feeding areas and resting sites. The range of the species extends from northern Sinaloa, Mexico, south into the Central American lowlands and the foothills of the Pacific coast in tropical deciduous forest. Three well-marked populations occupy this range. These are designated subspecifically as clarae in the north, eburnirostrum from Michoacan to Oaxaca, and canicularis in the south (Friedmann, et al., 1950: 126). The last two races mentioned are to be considered here. They are easily separable, the former having less orange on the forehead and a blackish splotch on the lower mandible, while the latter has a large patch of orange on the forehead and only the faintest wash of gray on the lower mandible (see extreme left and right subjects in "Step 7," Figure 1). Aratinga astec may be considered the ecological counterpart of A. canicularis in similar (but more mesic) habitat on the Atlantic slopes of Mexico and Central America. A. astec averages slightly smaller and is generally similar to A. canicularis in plumage, but lacks markings of orange, blue, and black on the head. In Aratinga astec, only a tuft of orange feathering is found above the cere. In captivity, the two species as observed by me were much alike in habits, including feeding, degree of sociality, agonism, epigamy, and voice. Although little published information is available concerning Aratinga astec, its biology in the wild state probably is closely similar to that of A. canicularis. All evidence in