SPECIES

Bahama Nuthatch Sitta insularis Scientific name definitions

Steven G. Mlodinow, Peter F. D. Boesman, Gary L. Slater, John D. Lloyd, James H. Withgott, and Kimberly G. Smith
Version: 1.0 — Published September 17, 2021

Plumages, Molts, and Structure

Plumages

The Bahama Nuthatch has ten functional primaries (the outermost reduced in length), nine secondaries (including three tertials), and twelve rectrices.

Juvenile / Immature

The plumage of juveniles matches that adults and immatures, except that the crown is gray rather than brown (1).

Adult

The crown of the adult is dull brown, contrasting moderately with a somewhat darker brown eyeline and lores. There is a distinct dirty whitish spot on the nape where the brown of the nape meets the blue-gray of the back. The back is entirely blue-gray as are the wing coverts, rump, and tail. The remiges and rectrices are a darker slate gray, with fresh remiges edged in pale gray. The rectrices lack white or have a diffuse white spot near the base of r1 (13). The alula is white or nearly white, and sometimes is visible as a rather obvious white mark near the bend of the wing. The undertail coverts and belly are gray transitioning through the chest to a dingy white throat and auriculars.

Molts

Molt and plumage terminology follows that of Humphrey and Parkes (14) as modified by Howell et al. (15, 16). The timing, extent, and sequence of molts have not been studied in the Bahama Nuthatch, though the Bahama Nuthatch is likely similar to the Brown-headed Nuthatch (Sitta pusilla) in following a Complex Alternate Strategy, including a partial preformative molt and limited prealternate molts in both first and definitive cycles (15, 11), but the timing may well differ as the two species appear to breed at different times of the year (1). Speculatively, the molts below are based on those of the Brown-headed Nuthatch (11), but due to the probable differences in nesting dates, no time frame is given.

Prejuvenile (First Prebasic) Molt

The prejuvenile molt is complete and takes place in the nest (17).

Preformative Molt

The preformative molt is incomplete and includes most to all body feathers and lesser and median coverts, sometimes (in ~33% of individuals) one to three inner greater coverts and (in ~43% of individuals) one to three tertials, but no primaries, primary coverts, secondaries, or rectrices (17, 18, 19, 13).

First and Definitive Prealternate Molts

The first and definitive prealternate molts are incomplete. The prealternate molt probably occurs on ventral feathers of some individuals (11). Norris (18) stated that no such molt occurs, but did not elaborate or provide data. Pyle (19) found that no wing coverts are replaced during a Prealternate molt. First and definitive molts are similar in timing and extent, as far as known.

Definitive Prebasic Molt

The definitive prebasic molt is complete (18, 19).

Bare Parts

Bill and Gape

Younger juveniles likely have yellowish color at the base of rictus as as is true in the Brown-headed Nuthatch, Sitta pusilla (18). The bill is pale sepia in juveniles, becoming blackish in adults. In adults, the upper mandible and distal lower mandible are slate-black while the base of the lower mandible pale is dull blue-gray.

Iris and Facial Skin

The iris is dark brown contrasting modestly with the pupil.

Tarsi and Toes

The legs and feet are dark gray, with brownish soles. The claws are blackish.

Measurements

Linear Measurements

Three Bahama Nuthatches were measure by Norris (18), one male, one female, and one unspecified. The means are as follows: Bill length 13.4 millimeters, wing chord 62.5 millimeters, tail length 30.6 millimeters, and tarsus length 15.2 millimeters.

Hayes et al. (1) states that the Bahama Nuthatch has a longer bill and shorter wing chord than the Brown-headed Nuthatch (Sitta pusilla), with the mean bill length of the Bahama Nuthatch shown as approximately 2 millimeters longer than that of the Brown-headed and the mean wing-chord of the Bahama between 2 and 2.5 millimeters shorter than that of the Brown-headed. Unfortunately, no specific numbers are provided (only a graph), and the source of the Brown-headed Nuthatch specimens was not provided. The source of those Brown-headed Nuthatch specimens matters as that species shows considerable geographical variation in linear measurements; for example, the mean wing length of Brown-headed Nuthatches from southern Florida is nearly 3 millimeters shorter than those from Maryland, and the mean bill length of northern Florida females was 0.76 mm longer than the mean for Maryland females (11).

Mass

Four birds from Grand Bahama Island were weighed as follows: nonbreeding-season males, 10.0 and 10.1 grams; nonbreeding-season females, 9.8 and 9.9 grams (12).

Recommended Citation

Mlodinow, S. G., P. F. D. Boesman, G. L. Slater, J. D. Lloyd, J. H. Withgott, and K. G. Smith (2021). Bahama Nuthatch (Sitta insularis), version 1.0. In Birds of the World (B. K. Keeney, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.bnhnut2.01