Posts Tagged ‘burrowing owl’

Some Plants and Birds that Favor Overgrazed Landscapes

May 25, 2014

Herds of Pleistocene megafauna were mobile and could never stay in one location for long or they would outstrip their food supply.  They seasonally traveled along the same corridors for decades or even centuries, until varying climatic changes altered their migration patterns.  During interstadials when forested conditions prevailed, grazers were forced to travel far and wide to satisfy their nutritional requirements, and during stadials when grassy environments were more common, the browsers had to migrate greater distances.  Many megafauna game trails led to valuable resources such as salt licks and water holes.  The megafauna greatly influenced the composition of plants, insects, and birds along these game trails, creating unique ecological associations and natural environments.  They trampled the ground, overgrazed and overbrowsed vegetation, debarked and killed trees, and unleashed large quantities of manure.

Most of the unique ecological associations formerly found on megafauna game trails no longer exist in North America, but the buffalo traces that early settlers encountered were a final relic.    Many buffalo traces led to the Blue Licks in Kentucky–a freshwater spring and salt lick.  The “immense” herds of buffalo had eroded the land everywhere here from up to 4-5 miles away.  Tree roots were visible due to this erosion.  Two species of now rare plants are thought to have been more abundant then because they depended upon habitat created by buffalo herds traveling along these traces.

Short’s goldenrod–a rare species known from only 3 sites.  These sites were formerly connected by a buffalo trace.

Goldenrod Soldier Beetle - Chauliognathus pensylvanicus

Goldenrod soldier beetle.  This is an important pollinator of Short’s goldenrod.

Short’s goldenrod (Solidago shortii) was discovered on Rock Island–a limestone outcrop located in the middle of the Ohio River Falls.  This was a former crossing spot for bison herds.  The Macalpine Lock and Dam later flooded this location, extirpating this population.  This species was later found growing on Blue Licks Battlefield Park in northern Kentucky and Harrison-Crawford State Park in Indiana.  All 3 known localities have 1 thing in common–they were formerly connected by the same buffalo trace.  Apparently, this species of goldenrod requires overgrazed trails, and they spread along this corridor, thanks to the bison.  It’s possible the goldenrod seeds were transported in bison dung.  Without trampling, grazing, and erosion, other species of plants outcompete and exclude this species of goldenrod.

Running Buffalo Clover–another rare plant that used to commonly grow on the buffalo traces.

Running buffalo clover (Trifolium stoloniferum) is another species now more restricted in range than in the past.  This is the only species of clover that does not have a rhizobial association.  All other species of clover and legumes have colonies of bacteria growing in their root nodules that help them absorb nitrogen.  However, running buffalo clover grew in patches frequently fertilized with nitrogen-rich bison dung, precluding their need for a rhizobial association.

Megafaunal trails likely had groves of wild fruit trees originating from seed-filled dung.  Persimmon, paw paw, plum, crabapple, wild squash, and passion fruit (maypop) probably were abundant on the sunny trails where large shade trees suffered high rates of mortality due to damage suffered from megafauna activity.  Dung beetles, scavenging birds, and predators all followed the mobile herds.  Thickets of shrubs and brier patches colonized abandoned megafauna trails and pastures, providing ideal habitat for rabbits.

Burrowing Owls

 

 

 

 

 

 

Burrowing owls prefer overgrazed cow pastures or frequently mowed golf courses and airports.

The burrowing owl (Athene cunicularia) has an odd present day range.  It mostly occurs in western North America, but a relic population lives in Florida.  Recent studies determined the relic Floridian population prefers overgrazed pasture land.  They like short grass with few trees, so they can have a good view of approaching predators.  They’ve actually expanded their range in the past century to include land cleared by humans such as golf courses, cemeteries, and airports.  However, they are considered threatened by increasing development that converts cow pasture to suburbs.  Burrowing owls must have occurred throughout much of eastern North America during the Pleistocene when game trails provided a network of suitable habitat.

Audubon’s Crested Caracara also requires overgrazed grasslands.

The crested caracara (Caracara cheriway) also occurs as a relic in south central Florida.  The rest of its range includes South America north to Texas.  Formerly, a coastal grassland habitat connected Florida with Texas, but during the Holocene forested habitat, unsuitable for this species, replaced this coastal grassland environment.  This is a scavenging bird that eats carrion, bird nestlings, disabled small animals, and insects.  They inhabit open ground where they search for food under woody debris and even cow dung.  Caracaras were also more widespread during the Pleistocene, but are more limited than burrowing owls because they are less cold tolerant.

Refererences:

Morrison, Joan

“The Crested Caracara in the Changing Grasslands of Florida”

Proceedings of the Florida Dry Prairie Conference 2004

Noss, Reed

Forgotten Grasslands of the South

Island Press 2013

The Similar Affinities of the Brown-headed and Pygmy Nuthatches

December 28, 2012

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/