Habits and interactions of North American three-toed woodpeckers (Picoides arcticus and Picoides tridactylus)

"Field studies of the little-known black-backed three-toed woodpecker (Picoides arcticus) and the northern three-toed woodpecker (P. tridactylus) during part of a breeding season in northern New York yielded much new information about the habits of the former species and some comparative data regarding the latter. Both species occur in the vicinity of spruce bogs where arcticus is more conspicuous and generally dominant over tridactylus. Picoides arcticus forages in dead trees, especially low dense or fallen trees, and tridactylus in live evergreen trees, generally higher up. The foraging sounds of arcticus were louder than those of tridactylus. Nest excavation, brooding, nest sanitation, and the feeding and behavior of nestlings are discussed for P. arcticus. Nestlings called almost continuously throughout the day. The female fed the young more often than did the male, but the male carried more food items per trip, and performed most of the nest sanitation. There are two distinct forms of drumming in P. tridactylus, both slower in tempo than the drumming of arcticus; drumming of these species is compared with four other sympatric woodpeckers. A kyik call (call note), screech call, five calls of a yeh call complex, kyik-ek call, snarl call, rattle call, and distinctive scream-rattle-snarl call are described for arcticus. Calls of tridactylus discussed are the pik (call note), the rattle, and the kweek. Vocalizations of these picids are compared, and the comparison is extended to closely related (and sympatric) P. villosus and P. pubescens. Three bill positioning postures, a hunched posture, crest raising display, head bobbing display, head swinging display, wing spreading display, flutter aerial display, and tail spreading display are described for one or both three-toed woodpeckers. Conspecific interactions, encounters between tridactylus and arcticus and conflicts of arcticus with villosus and other species are discussed. The data support the relationship of arcticus and tridactylus with the North American assemblage of Picoides. They further suggest that tridactylus has diverged less, and arcticus more from their common ancestor. Specialization of arcticus as it evolved in a milieu of related North American congeners probably was a factor permitting tridactylus to invade North America successfully from Eurasia in the recent past"--P. 3.