The Similar Affinities of the Brown-headed and Pygmy Nuthatches

The brown-headed nuthatch (Sitta pusilla) and the pygmy nuthatch (Sitta pygmaea) both descend from a common ancestor that used to range all across the North American continent.  Now, the former inhabits the southeast, while the latter lives in disjunct populations scattered across the southwest.  They are similar in size, appearance, and habitat preference.  The pygmy nuthatch has a darker brown cap than the brown-headed nuthatch, and its tail has white spots not found on its cousin, but otherwise they are physically identical.  Both favor mature pine forests prone to frequent fire.

Brown-headed nuthatch in its usual position, perched upside down on  a tree trunk.  They live in mature southern pine forests and originally were abundant in long leaf pine savannahs.

Range map of a brown-headed nuthatch.  I suspect the average abundance figures on this map are misleading.  They are probably more abundant on the coastal plain than the piedmont, but more people live in the piedmont and report seeing them there.

Pygmy nuthatches live in Ponderosa pine forests out west.

Range map of the pygmy nuthatch.

Fossil evidence of a small forest-dwelling bird, such as a nuthatch, is understandably scarce, yet does exist.  The oldest fossil specimen from the Sitta genus dates to early in the Miocene (~23 million years ago) and was excavated in France.  In North America 2 specimens of nuthatches dating to the middle Pleistocene (~600,000 BP) were found in Porcupine Cave, Colorado.  One was positively identified as the still extant white-breasted nuthatch (Sitta carolinensis).  Brown-headed nuthatches and pygmy nuthatches became geographically isolated from each other during the latter stages of the Pleistocene.  A desert scrub and grassland corridor existed during the early and middle Pleistocene that linked southeastern North America with the west.  During some undetermined time in the mid to late Pleistocene ecological changes closed this pathway for some species.  Like burrowing owls and Florida scrub jays, brown-headed nuthatches became isolated from their western populations.  In the cases of the jays and the nuthatches, speciation occurred between the eastern and western populations.  As far as I know, no attempt has ever been made to see if these 2 species of nuthatches would interbreed in captivity.  I bet they could.

Ponderosa pine forests were reduced to 2 refuges durng the Last Glacial Maximum when they were displaced by spruce forests.  Studies of pygmy nuthatch genetics suggests they only survived in 1 of the refuges.

Nuthatches are smart birds that use chips of bark to probe for insects burrowing in wood.  Seeds are also an important part of their diet.  Family groups usually consist of a male, female, and a male offspring who helps take care of the nestlings.  The annual survival rate is about 70%.  The brown-headed nuthatch has an outlying population in the Bahamas where it lives in Carribbean pine forests.  Prospects for survival there are doubtful because developers are going to eliminate all of the pine forests, none of which are protected by nature preserves.

I’ve never seen a brown-headed nuthatch, though supposedly they range into Augusta, Georgia.  However, I did see a white-breasted nuthatch at the Silverbluff Audubon Center in Silverbluff, South Carolina.  See https://markgelbart.wordpress.com/2011/11/28/the-silver-bluff-audubon-center/

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One Response to “The Similar Affinities of the Brown-headed and Pygmy Nuthatches”

  1. tinatimebomb Says:

    Did you get your star award? http://cherryberrylemonlime.wordpress.com/2012/12/22/merry-christmas-my-first-star-award-im-passing-it-forward-look-and-see-if-its-you/

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