The Whooping Crane (Grus americana) is among North AmericaÂs most
charismatic species. Between 1938 and 2004, the population that migrates between
Aransas National Wildlife Refuge (ANWR) and Wood Buffalo National Park (WBNP),
grew from 18 to 217 individuals. The recovery plan objective for this endangered
species is to downlist the population in 2035, but this requires interpretive assessment of
population responses to environmental factors over the long term. I analyzed 27 years of
banding data, 37 years of nest monitoring data, and 20 years of winter reports to estimate
age-specific mortality and fecundity rates. The resulting life table yielded an intrinsic
rate of increase (r) of 0.14/y, a net reproductive rate (Ro) of 6.4/y, and a mean length of
a generation (G) of 13y.
Path analysis of environmental factors, demographic variables (natality and
mortality), and the finite rate of population increase (lambda) showed that annual
mortality, temperatures from the ANWR, WBNP and at a migration stop-over in Nebraska, and pond water depth were good predictors of lambda variability. However,
other environmental factors were significantly correlated: at ANWR, October- March
temperature (extreme minimum and maximum), December temperature (mean and
extreme minimum), November-January precipitation, and September-March freshwater
inflow; at WBNP, March-September precipitation, March-May temperature, and
temperatures during the September - October fall migration. The Pacific Decadal
Oscillation (PDO) affected lambda indirectly through environmental factors in Nebraska
and ANWR.
I graphically analyzed relevant data trends from 1967 to 2004 to identify the
relation between phases of PDO and environmental and demographic variables. During
PDO cold phases, a synchronization of Âextreme environmental values was observed
from the different regions; during warm phases extreme environmental values were
scattered. Most periods of Whooping Crane population decline happened during cold
phases.
I developed a compartment model to represent Whooping Crane population
dynamics utilizing the new data on survivorship and fecundity from banded birds. The
model was capable of simulating historical population trends with adjustments in brood
success and egg mortality. The model will allow future studies to test population
responses to various environmental scenarios at the WBNP, during fall and spring
migrations, and at the ANWR.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3778 |
| Date | 16 August 2006 |
| Creators | Gil de Weir, Karine |
| Contributors | Grant, William E. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 2409224 bytes, electronic, application/pdf, born digital |
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