Prealternate Molt in Nuthatches

Nuthatches of the genus Sitta constitute one of the passefine groups in which prealternate (prenuptial) molt is generally believed not to occur.Dwight (1900: 298) discussed this genus with the family Paridae and stated: "All the members of this family have only the annual moult.They are peculiar in assuming a juvenal plumage closely resembling the pale nuptial plumage which results from extreme fading of the winter dress."Witherby (in Witherby et al. 1938: 244) remarked that in S. europaea the summer plumage is attained by abrasion rather than by molt.Following Dwight's analysis, Bent (1948) recorded that the prenuptial molt did not occur in S. carolinensis or S. canadensis.Although Norris (1958: 246) found several females of S. pygmaea that were replacing feathers in the nuchal region in March and April, he regarded this as a regrowth of feathers lost in social interactions rather than as prealternate molt; the replacement of contour feathers "over nearly every part of the body" in early April by one female of that species was considered to be "an aberrant instance of prenuptial molt."Norris (op.cit.) stated categorically that "There is no prenuptial molt in Sitta pusilia."For most species in the genus, however, I have been unable to find any statement, even a negative one, concerning the occurrence of this molt.On the other hand, there is a partial prealternate molt in the seasonally dimorphic Tichodroma touraria, usually considered a member of the family Sittidae but in a different subfamily.While studying Red-breasted Nuthatches, S. canadensis, for other reasons (Banks 1970), I noticed a Sittaformosa.--Specimenswere not available to indicate periods of molt.Sitta azurae.--IndividualsofS.a. expectata from 22 February and 16 March have feathers in sheath on the throat and on the throat, breast, and back, respectively, although six other specimens taken from February to May are not molting.Four specimens of the race S. a. azurae are molting body feathers in March and April, although one from April and one from September are not in molt.The spring-taken molting birds seem to indicate a well-marked prealternate molt in this species.Sittafrontalis.---Two male specimens (S.f.frontalis) taken 5 and 18 April in Tenasserim, Burma, have incoming feathers on the mid-back.Preparation of these specimens is poor and signs of possible molt on the ventral surface may have been lost.There is no molt of remiges, and these high altitude birds may be in a prealternate molt. DISCUSSION A partial prealternate (prenuptial) molt occurs in at least some individuals of many species of nuthatches in the genusSitta.There appears to be a correlation in the proportion of individuals of a species which undergo this molt and the extent of the molt in an individual bird.Thus, many individuals of S. canadensis molt prior to the onset of the breeding season, and the replacement of feathers by each bird may be quite extensive.On the other hand, a small proportion of S. carolinensis molt, and only a few feathers are replaced in those individuals.The species of Sitta can be grouped tentatively according to the extent of the prealternate molt, as follows: (1) Molt extensive and occurring in a large proportion of individuals•canadensis, pygmaea, azurae, frontalis; (2) Molt slight and occurring in a small proportion of individuals--pusilla, carolinensis, neumayer, europaea, yunnanensis, leucopsis, krueperi, magna; (3) Apparently no molt--4ephronota, himalayensis.In the remaining species•whiteheadi, villosa, formosa--the occurrence of this molt was not determined.By virtue of their habits and manner of feeding, nuthatches are subject to considerable wear, and indeed the ventral plumage, particularly in species which dwell largely in pines, becomes quite abraded by the time that nesting begins.It is probably significant that where some prealternate molt occurs it is chiefly the ventral body feathers that are affected.I appreciate the courtesies of George E. Watson, Xavier Misonne, and the curators of the American Museum of Natural History in permitting me to examine specimens under their care.