Whooping Crane Soars to Another Record High
By Tom Stehn, Whooping Crane Coordinator, USFWS
February, 2008
The tallest
bird in North America has something special to “whoop” about.
In December 2007, census flights at the Aransas National Wildlife Refuge
and surrounding areas documented a record flock size of 266. The flock
consists
of an estimated 142 adults, 85 subadults, and 39 juveniles. These are
the highest numbers of endangered whooping cranes wintering in Texas
in approximately the last 100 years. The current population exceeds by
29 the previous high of 237 whoopers present in the fall of 2006.
Excellent Chick Production in Summer 2007
The estimated flock size of 266 is a result of excellent production (from
a record 65 nests) of 40 juveniles sighted on the nesting grounds in
August just prior to fledging. With 39 juveniles arriving safely in Texas
this winter, survival of the juveniles since August was excellent. One
carcass of a juvenile was found in the fall in Saskatchewan with the
cause of death unknown.
Good Adult Survival Rate Compared to Previous Two Years
Adult survival since last spring has also been
very good. Mortality of white-plumaged cranes between spring and fall,
2007 was at most 9 birds, or 3.8% of the flock present at Aransas in
spring, 2007. This is calculated by taking the spring flock size (236),
adding the number of juveniles that made it to Texas (39), and subtracting
the current estimated flock size (266). In the previous two years, mortality
between spring and fall has been above average and totaled over 20 birds
each year. One indication of adult mortality in 2007 subsequent to nesting
was the arrival of one adult with one chick seen in Saskatchewan in the
fall and at Aransas during the winter.
Noteworthy Cranes
One of the surviving 39 juveniles was sighted with sandhill cranes at
Muleshoe NWR in west Texas in November and is wintering at an unknown
location. One whooping crane apparently resumed its migration from North
Dakota on December 22nd. This is the furthest north a whooping crane
has ever been located just before Christmas. All the water bodies were
frozen so the crane was roosting in a shelterbelt and feeding in agricultural
fields. At Aransas, especially notable is one whooping crane pair with
two chicks. Although whooping cranes normally hatch two chicks every
year, usually only one of the youngsters is able to survive. The pair
with two chicks has a territory on the south tip of Aransas and are the
first cranes the tour boats usually see once they reach the refuge, providing
the public a great opportunity to see the family of four. They are the
13th two-chick family to reach Aransas since 1997 when the egg pickup
was halted.
Flock Growth in the Face of Threats
The
population in Texas reached a low of only 15 birds in 1941 before efforts
were taken to protect the species and its habitat. The population
has been growing at about four percent annually; it reached 100
birds in 1987 and 200 birds in 2004. However, the whooping crane population
continues to face many threats, including collisions with power
lines in migration, development of wind power in the migration corridor,
limited
genetic variability in the flock, loss of crane migration habitat,
and winter habitat threatened with housing developments, chemical spills,
sea level rise, and loss of productivity due to reduced fresh water
inflows.
The Only Natural Wild Whooping Crane Population
The only natural wild whooping crane population nests in the Northwest
Territories of Canada in summer and migrate 2,400 miles to winter
at the Aransas and Matagorda Island National Wildlife Refuges
and surrounding
areas. Their winter range stretches out over 35 miles of the
Texas coast about 45 miles north of Corpus Christi, Texas. Wintering
whooping cranes
use salt marsh habitat foraging primarily for blue crabs. Unlike
most other bird species, whooping cranes are territorial in both
summer and
winter and will defend and chase all other whooping cranes out
of their estimated 350-acre territories.
Counting
the Cranes: Reasons and Challenges
It takes about seven hours of flying to cover about 56,000 acres
of marsh to find all the cranes. These flights determine
flock size, locate crane
territories, and mortalities that may occur during winter.
Finding every whooping crane is quite a challenge with thousands
of other
white birds
in the marsh, including pelicans and egrets, that makes spotting
of cranes more difficult. Also, the cranes can move during
a census flight and
either not be counted or else be counted twice. Census flights
are contracted with Air Logistic Solutions of San Antonio,
Texas in a Cessna 210 high-wing
aircraft with Pilot Gary Ritchey.
A Conservation
Comeback to Celebrate
The February 2008 total North American population of wild (378)
and captive (146) whooping cranes is 524. Although the
whooping crane
population
remains endangered, the comeback of the species sets a
standard for conservation efforts in North America.
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