Buitron, D. 1988. Female and male specialization in parental care and its consequences in black-billed magpies. Condor 90. pp. 29-39.
The breeding biology of a small population of individually marked Black-billed Magpies (Pica pica) was studied from 1978 through 1981 in Wind Cave National Park, South Dakota. Mates cooperated extensively in nest building defense of nest site, and care of eggs, nestlings, and fledglings. The two sexes specialized in different types of parental care, with the result that both parents were needed to fledge young. Of the types of parental care that the author was able to measure, males contributed more than females to raising young and were also more active in expelling intruders and driving away predators. Feeding of young peaked the week after fledging and parental care continued for another 5 to 6 weeks.