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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The Silver Bluff Audubon Center

I planned to visit the Moody Nature Preserve over Thanksgiving break, but I changed my mind because I hate driving.  Instead, I went to The Silver Bluff Audubon Center near Silver Bluff, South Carolina.  It was a 45 minute drive from my house vs. a 3 hour drive to the Moody Preserve.  The shorter distance beat sitting in a car half the day.

The SBAC is located in the boondocks.  Silver Bluff Road runs off Old Jackson Highway, an area of second growth forest, agricultural land, and factories.  The latter are located here to take advantage of the state’s anti-union oppression.  A large wheat field borders the bird sanctuary.  The last 2 miles of Silver Bluff Road consists of unpaved but well graded dirt.  The road leads to the Savannah River but to reach the hiking trails it’s only necessary to drive about half that distance.

Map of the SBAC. I hiked the Tanager Loop Trail.  It’s supposed to be about 2 miles, but I think it’s slightly longer than that.  The Tanager Trail is well marked and easy to follow.

This ancient dwelling is near the beginning of Tanager Trail.  It looks like an outhouse, but someone probably lived in it a long time ago.  Perhaps it was a hunting cabin.  It’s surrounded by overgrown chinaberry trees (I think).

Over 200 species of birds have been recorded at the SBAC, and I saw about 5 % of them in the hour I was there.  I suppose, if I could have stayed all day, I could have easily doubled that number.  I didn’t see any of the rare birds that make this preserve special–bald eagles, Cooper’s hawks, wood storks, Bachman’s sparrows, prairie warblers, Swainson’s warblers, and loggerhead shrikes.  All of these species breed here, but some are migrants.  I didn’t see the ponds where the water level is managed for the wood storks.  Wood storks require shallow water that supports an abundance of small aquatic vertebrates.  They nest close to shallow water, making it easy to feed their young.  I did see a wood stork last spring around the corner from my house as it flew over a wooded stream.

The 10 species of birds I did see were common–white breasted nuthatches, Le Conte’s sparrows, downy woodpeckers, rufous sided towhees, mourning doves, cardinals, crows, redwinged black birds, and turkey vultures.  This was the first time I’d ever noticed and identified the white breasted nuthatch, though I realize now I’ve seen them many times in the past.  They occur in pairs, and I did see 2 flying together.  The other hiking trail is actually named the White Breasted Nuthatch Trail.  On the way to this preserve I drove on bridges over Phinizy Swamp, Merry Brickyard Ponds, and the Savannah River, and I spotted 4 additional species–black vultures, common mergansers, great blue herons, and egrets.  None of the birds in the SBAC cooperated with my attempts to photograph them.  They kept flitting about and perching high in the trees.

There’s an open pine savannah with longleaf pine and wire grass alongside the unpaved road that leads to the trails, but I didn’t stop to photograph it.  I didn’t see any longleaf pine trees along the trail I hiked, though much of the forest is quite open there, and the fires they use to manage the savannah have undoubtedly spread here.

Much of the forest in the SBAC is open like this.  It consists of a few species of pine and many species of oak.  These are loblolly pine, I believe.  Shortleaf pine and loblolly pine hybridize and some of the trees showed characteristics of both.

Many of the pine tree trunks are charred, showing evidence of fires.  The fires used to manage the open pine savannah evidentally spread here.  Both pines and oaks are fire resistant.  Most pine and oak trees over 3 years old can survive light ground fires.  Some species of oak, however, are somewhat less fire resistant.  They may survive, but the fire damage makes them vulnerable to diseases which rot out the wood and create snags.

Here’s an oak tree that was wrecked by a storm, probably earlier this past summer.

Common trees along the Tanager Trail that I identified include loblolly pine, shortleaf pine, hybrid pines, water oak, laurel oak, Shumard’s oak, southern red oak, black or cherry bark oak (I can’t tell the difference), blackjack oak, swamp chestnut oak, post oak, overcup oak, sweetgum, hickory, beech, and tupelo.  The composition suggests what botanists might refer to as a mesophitic river terrace forest because most of the species prefer moist sites.  I had never noticed and identified Shumard’s oak before, though I’ve certainly seen it.  Shumard’s oak can grow to 100 feet tall.  It’s a valuable species utilized for reforesting bottomlands due to its fast growth rate.  Swamp chestnut oak occurs here as well.  It’s also known as cow oak because its acorns are palatable enough for cows to eat.

Spanish moss grows on most of the hardwoods here.

Is this a dried out Carolina Bay?  I took this photo while standing on a boardwalk, but last summer must have been so dry the water here completely evaporated.  Tupelo trees grow here.  They normally grow partially submerged.  I think this might be a Carolina Bay.

There’s lots of snags in these woods.

The tree on the right is a beech.  I’m always excited to find this northern species in Georgia.  I couldn’t identify the tree on the left because the leaves had all fallen off, but there were a lot of hickory leaves on the ground around the trunk.

Note the woodpecker hole at the very top of the debarked tree.  Did the woodpeckers debark their nesting tree?

A windstorm knocked this tree precariously over the trail.  Several other trees were knocked over in a neat row.  Tornado or downburst?

Photo of the trunk of the leaning tree in the previous photo.  The base is cracked.

The trail goes through a planted pine plantation.  I couldn’t believe the trail sign pointed this way.  I thought some practical joker had twisted the sign because a trail criscrossed this one.  Luckily, I did follow the sign.  Trees are harvested here, but for the most part the management is beneficial for the birds.  This was the dullest part of the trail, though a big flock of redwinged blackbirds flew over us here.

I saw deer tracks and heard a squirrel barking–the only mammal life I detected here.  Surrounding this deer track are fallen leaves from laurel oak, water oak, and overcup oak.

If I would have had more time I would have walked down the unpaved road to the river.  I hiker can easily get over 5 miles of enjoyable walking here on the trails and unpaved road.  On the Friday after Thanksgiving there were only 2 other cars parked here, so it’s not at all crowded.