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WHITE-FACED IBIS: AN INDICATOR SPECIES |
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Problem/Background
Approach/Objectives
Results from contaminant analysis of blood taken from
the PTT-marked white-faced ibis revealed contamination levels similar
to those of previous years. Results from plasma reveal three contaminated
birds (30%), with high DDE levels in the blood. Four birds (40%) had low
levels of DDE, and the remaining three (30%) had non-detectable levels.
The table above details the DDE levels, by bird. These results suggest
that there still is a contaminants problem with a portion of the Carson
area breeding population. In the spring of 2003 10 white-faced ibis nesting at Stillwater NWR were PTT marked. This began the second and final year of prey sampling and analysis. As of this writng (May 2004) prey samples from wintering grounds have been taken and shipped to the lab for analysis.
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characterize
the Great Basin region. A ban on the use of DDT (an agricultural pesticide)
in this country a quarter century ago has resulted in the dramatic recovery
of most affected species. But ten years ago, a significant segment (approximately
45%) of the white-faced ibis breeding population in western Nevada was
found to be burdened still with high levels of DDE, the principal metabolite
of DDT. The results were eggshells 18% thinner than normal, and a 20%
decrease in breeding production. This situation has not changed, and researchers
have determined that these contaminants are not being acquired in western
Nevada. Just where and how these birds are being contaminated with DDT
remains a mystery. Furthermore, an increase in eggshell thinning by just
2% could result in extensive reproductive failure, which could place this
species on a direct path for action under the Endangered Species Act.
backpack
transmitters weighing approximately 27 grams each. These backpacks included
satellite and conventional VHF telemetry transmitters. This was an initial
pilot test to determine whether the white-faced ibis could carry this
kind of transmitter package. These birds were monitored daily, along with
others involved in a conventional radio telemetry study being conducted
by the Refuge. Argos satellite-derived positions from these two white-faced
ibis confirmed movements throughout the area and revealed some unexpected
daytime round-trips over a mountain range to and from foraging areas in
an adjacent valley. The satellite transmitters lasted into the autumn
migration, and we were able to track the two birds to the southern region
of the Central Valley of California before the batteries failed.
captured,
blood-sampled, and outfitted ten white-faced ibis with satellite transmitters
weighing 20 grams to track them on their annual migration; we hope to
ascertain where the birds might be picking up DDT contamination (map below
is through 11/14/00). Blood analyses from these ten ibis indicate that
three were “hot” with DDT contamination. CCRT will carefully
track these three hot birds to identify wintering areas. There, we will
sample the birds’ prey (largely worms) and test for DDT contamination.
Over the course of another year of satellite tracking and monitoring,
we should be able to map out exactly where these DDT hot spots are. It
is significant to note it is likely that other species of birds are also
being exposed to this same contamination threat. 
Contaminant
Analysis: