Posts Tagged ‘loggerhead shrikes’

Pleistocene Pastures and Loggerhead Shrikes (Lanius ludovicianus)

January 18, 2016

The habitat requirements of the loggerhead shrike suggest a long interrelationship with extinct Pleistocene megafauna.  Shrikes prefer grazed grasslands with nearby thickets of short trees for nesting and isolated taller trees for perching.  A cow pasture adjacent to a large yard landscaped with trees and bushes is ideal habitat for a shrike.  Shrikes use the isolated trees as observation posts where they search for prey.  A grazed pasture maintains just the right height of grass so a shrike can find their favorite foods–grasshoppers, mice, lizards, small snakes, and other song birds.  Grass that gets too tall could also conceal a predator such as a fox or cat not averse to making a meal of shrike.  Thickets provide good places for shrikes to hide their nests.  During the Pleistocene mammoths, bison, and horses maintained the range of habitats required by shrikes, the haphazard mix of grazed pasture, isolated tall trees, and thickets.  Despite the unlikelihood that a predatory songbird could become preserved in the fossil record, shrike remains dating to the Pleistocene have been excavated from 2 fossil sites in Florida at Arredondo and Reddick.  Shrikes were probably common in the southeast for millions of years, and they surely witnessed herds of megafauna stirring up prey.  The ancestor of the loggerhead shrike diverged from a Holarctic population of northern shrikes (Lanius excubitor) when Ice Ages began occurring, and glaciers isolated the founding population.

A great grey shrike with an impaled mouse. Photo courtesy of Marek Szczepanek. Source.

A great gray shrike with a mouse it impaled.  They kill their prey by snipping the spine behind the head.  Their claws are too weak to hold on to their prey when feeding and tearing with their bill, so they impale them on thorns or barbed wire.

Following the extinction of the megafauna, shrikes remained common in the southeast.  Fire and Native American agricultural practices maintained favorable shrike habitat.  The characteristics of sand hills with widely spaced pines, scrubby thickets, and sparse ground cover were always a preferred habitat for shrikes.  When William Bartram traveled through the Florida sand hills in 1776 he noted that shrikes (or butcher birds as he called them), along with rufous-sided towhees and Florida scrub jays, were “very numerous.”  He described this landscape as an open pine and palm savannah interspersed with thickets of magnolia, dwarf oaks, devilwood, blueberry, pawpaw, and buckthorn.  In 1939 John May wrote in his classic A Natural History of North American BirdsThe Loggerhead Shrike is an extremely common bird along the roadsides of Florida, where in winter every third or fourth telephone pole seems to serve as an outlook point for either a Mockingbird, a Sparrow Hawk, or a Loggerhead Shrike.”

Unfortunately, loggerhead shrike populations have drastically declined over the past 60 years. I’ve never seen one.  A century ago, before the adoption of the car, horse pastures were abundant across the southeast.  Farmers still raised cattle on all this excess pastureland for decades after cars replaced horse and buggies.  Cotton and corn fields left fallow covered much of the south as well.  Fallow fields rank 2nd to pasture as good shrike habitat.  Much of this favorable shrike habitat has been converted to pine plantations, a type of environment that supports no wildlife.  This ecological disaster also explains declines in the populations of eastern meadowlarks, vesper sparrows, grasshopper sparrows, and bobwhite quail.  In Louisiana and Texas the conversion of cow pastures to rice plantations has caused a decline in shrike populations there.  Invasive fire ants colonize the bare earth left after the rice is harvested, and they compete for the same prey items.

Shrikes are permanent residents in the south.  Shrikes that breed in the Midwest migrate south during the winter.  These migratory populations are suffering an even worse decline.  Territorial shrikes that permanently reside in the south drive away migratory pairs from the remaining suitable habitat.  Migratory shrikes have become extirpated from many areas where they formerly ranged.  One study of shrikes in the North Carolina sand hills region determined that shrikes are disappearing from the periphery of their range, but core populations living in good shrike habitat are stable.  I hope they remain so.  The loggerhead shrike is on my birding wish list.

References:

Lynn, Nadine; and Stanley Temple

“Land Use Changes in the Gulf Coast Region: Links to Decline in Midwestern Shrike Population”

The Passenger Pigeon 1991

McNair, Douglas

“Breeding Distribution and Population Persistence of Loggerhead Shrikes in a Portion of the North Carolina Sandhills”

The Southeastern Naturalist 4 (14) 2015

 

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Carvers Creek State Park in South Central North Carolina

October 27, 2015

Last Saturday, we visited my nephew who is stationed at Fort Bragg in North Carolina.  This gave me the opportunity to hike around Carvers Creek State Park located nearby.  Past the entrance, a long wide path borders an old field on one side and a woodland of shortleaf pine with an understory of blackjack oak and sweetgum saplings on the other side.  I heard a constant chirping of crickets in the field, and grasshoppers were also abundant.  This is ideal habitat for loggerhead shrikes (Lanius ludovicianus), a species in decline.  They nest in short trees but hunt for large insects (such as grasshoppers), mice, lizards, amphibians, and even juvenile venomous snakes; all of which can be found in this old field.  I’ve never seen a loggerhead shrike, and it’s high on my birding wish list.  I asked a park ranger where the shrikes were.  She told me they could usually be seen behind a fence where they keep their maintenance equipment, and birders using binoculars could stand near the fence and see them.  I didn’t have binoculars with me, so shrikes are still on my wish list.

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The first part of the trail borders an old field humming with crickets and grasshoppers.  Loggerhead shrikes inhabit this park.

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Much of the park is open woodland/savannah type environments.

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Big loblolly pine.

This path leads to the former winter house of one of the Rockefellers, but it is not yet open to the public.  The state park service probably needs to renovate it, so it’s safe for visitors.  Rotten floor boards can be hazardous.  It overlooks a millpond and has glassed-in porches on the 2nd floor of both the front and the back.

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The front of the WWI era Rockefeller winter home.

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Back of the Rockefeller winter home.  Most of the wildlife I did see was here behind the fence.  Note the glassed-in porch.  Nice.  It overlooks the millpond.

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Cypress trees ring the millpond.

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Millpond.

A live oak tree grows near the Rockefeller house.  Live oak is not native to North Carolina this far inland, though it does grow near the coast.  This specimen must have been transplanted here over a century ago.  I saw gray squirrels, chipping sparrows, and blue jays foraging on acorns under the tree.  One of the squirrels was rather large, and at first I thought it might be a fox squirrel, but I caught a glimpse of white underbelly.  Gray squirrels usually have white bellies, while fox squirrels are solid-colored.  The ranger told me fox squirrels can be seen on the loop trail around the millpond, but I didn’t see them.

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Live oak.

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The loop trail goes through a savannah.

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More open woodland/savannah.

I was surprised to see cypress trees growing this far inland.  Cypress trees grow on the edges of the millpond here.  I checked the range map and learned this site is about as far inland as they can normally be found.

The loop trail threads through open pine savannah.  I noticed fire marks on some of the pines.  This park must be managed with fire.

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The millpond is u-shaped. Note the cypress trees in the water.

Carvers Creek Park is a recent and valuable addition to North Carolina’s state park system.  Much of the area around the park has been transmogrified into pine tree farms, an environment that supports almost no wildlife at all.