Territorial Relationships between Cardinals and Pyrrhuloxias

The Check-list committee of the American Ornithologists' Union (1957) and Hellmayr (1938) maintain the Cardinal (Richmondena cardinalis) and the Pyrrhuloxia (Pyrrhuloxia sinuata) in separate genera.However, others (Mayr and Amadon, 1951) have indicated that these two species may be congeneric.The existence of a second species of Cardinal (Richmondena phoenicea) , which shows tendencies in bill structure toward the Pyrrhuloxia, further suggests the possibility that the two are congeneric.Ridgway (1901) separates the two genera primarily on the basis of bill structure.Although these differences are valid, the question arises as to whether they may be utilized as so-called "generic" characters in this case.Simpson (1945) points out the basic aspect of the genus as a group of similar species.The concept does not regard the genus as a hierarchical category based on one or few character differences but rather as one which stresses groups of similar characters shared by a natural evolutionary group of species.In the absence of paleontological evidence we must rely on similarities displayed by the present day forms.In this respect, ecology and life history are as important considerations as are morphological characters.Territory in birds has received much attention in recent years.Hinde' s (1956) excellent review shows the great differentiation that exists among species which might be used to throw light on relationships.Our best understanding of the value of territory in this connection should come from a comparison of two closely related species which occur together and utilize the same habitat.Several recent studies have been conducted on the relationships between similar species in areas of overlap.These have shown various degrees of relationship depending on the similarity and/or difference between the two species.Lanyon ( 195 7) found in the very similar and closely related meadowlarks that when both species occur in the same area they hold mutually exclusive territories.The two species of towhees studied by Marshall (1960) are separated by more effective isolating mechanisms, and their territories overlap broadly where the two are found together.This paper summarizes the results of a field study on the Cardinal and Pyrrhuloxia in an area where both occur as abundant residents.ACKNOWLEDGMENTS For financial assistance during the summer of 1959 I am indebted to the Frank M. Chapman Memorial Fund of the American Museum of Natural History.I wish to thank Wendell Taber, A. H. Anderson, and A. R. Phillips for supplying references and suggestions utilized in this paper.Joe T. Marshall, Jr., originally suggested the problem and permitted me to share his transportation and field equipment.Acknowledgment is also given to the tribal council of the Papago Indian Reservation for permission to conduct field studies within the reservation.The maps used in this paper are modified from those used by Marshall (1960).METHODS AND STUDY SITE A 42-acre area in the San Xavier Indian Reservation, ten miles south of Tucson, Pima County, Arizona, was selected as a study site.This is the same area utilized by Marshall ( 1960).The site is situated on the first-step lowlands of the Santa Cruz River, and it contains mesquite (Proso$-is julijlora) woodland with an understory of gray-thorn (Condalia Zycioides) .Elderberry (Sambucus) and hackberry (Celtis) are common in hedgerows.Much of the mesquite has been cut out and the fields have been cultivated, 246