abstracts of oral and poster presentations - Pacific Seabird Group

chases, and rates of thievery. In the second of two years, we conducted a food-supplementation experiment on
six individually marked pairs during 18 days of incubation. We hypothesized that, if time allotted by territorial
gulls to territorial attendance is related to prey abundance within territories, then experimentally increasing prey
quantity should lead to increased attendance. Females responded by increasing total time within their territory,
both in incubation and non-incubation. Males reduced incubation time, but conversely increased non-incubation
attendance. Intrusion duration and egg thievery occurred most often during absence of the non-incubating
partner. We believe individuals in this system compensate for shortcomings in abundance of prey within their
territories by foraging extra-territorially. However, this trade-off is modulated by the cost of increased prey
depletion due to thievery by intruders occurring when territory “owners” are absent.
EFFECTS OF EMERGENT VEGETATION ON WAVE ATTENUATION AND ITS SIGNIFICANCE FOR
OVER-WATER NESTING BIRDS
Joseph Allen* (joseph.allen.1@ndsu.nodak.edu) and Gary Nuechterlein; Department of Biology, North Dakota
State University, Fargo, ND USA
Wind and wave action affects nesting success of many over-water nesting birds. Colonial grebes are
particularly vulnerable to these factors, because they establish floating platforms within emergent beds. In
Western Grebes (Aechmophorus occidentalis), wave action commonly accounts for over 50% of nest losses in
colonies, and entire colonies may often be destroyed by major windstorms. Wave attenuation by dense
emergent beds can be substantial, and survival of nest platforms in a colony of over 80 nests was related
primarily to their distance from the exposed outer edge. In this study, we are examining factors important in
predicting the degree of wave exposure that a nest platform experiences. These include water depth, fetch, wind
speed, and density of submerged and emergent macrophytes. During the preliminary field season, we quantified
maximal wave height and examined the dampening effects of different densities of bulrush (Scirpus spp.).
These results have serious implications for management of waterbird nesting habitat. Our study site, Lake
Christina, Minnesota, was treated with rotenone in October 2003 in an attempt to stimulate a trophic cascade
leading to an increase in macrophytes. If successful, restoration of the aquatic vegetation may lead to an
increase of waterbirds using the lake.
COMPONENTS OF REPRODUCTIVE IMPAIRMENT IN CONTAMINATED WESTERN/CLARK'S
GREBES FROM CENTRAL CALIFORNIA
Daniel W. Anderson (dwanderson@ucdavis.edu); Dept. of Wildlife, Fish, & Conservation Biology, University
of California, Davis, CA USA
In the mid-1950s, the insecticide p,p’-DDD was the major proximate cause of severely depressed
populations of Aechmophorus grebes at Clear Lake, in central California. Today, some 50 years later, grebes
have improved from the effects of DDD but still suffer reproductive impairments from a suite of proximate
causes. Here, I evaluate the major multiple-stressors (organo-chlorines DDD and DDE, methyl mercury, habitat
change, and disturbance) and I estimate their relative roles. Since DDD is not converted to DDE in natural
systems, DDE must originate from the past use of DDT. Clear Lake grebes still suffer chronic DDE-induced
eggshell thinning, but DDD levels, although still present as a distinct “Clear Lake fingerprint”, are probably no
longer important toxicologically and have declined by several orders of magnitude in all ecosystem components
measured. Methyl mercury, now known to have been present in Clear Lake grebes even during earlier DDD
studies, is declining, but some levels are still close to those that have effects on developing embryos and adult
liver function. Yet, human disturbances in the last ten years have by far been an over-riding factor depressing
reproduction. The suite of stressors has resulted in a chronically low negative effect on reproduction at
comparison sites, so that Clear Lake is still a “sink” relative to “source” populations at Eagle Lake and Tule
Lake, in northern California.
SEABIRD RESTORATION PROJECTS TO COMPENSATE FOR THE 1998 COMMAND OIL SPILL
[Poster]
Charlene A. Andrade 1 (Charlene_andrade@fws.gov), Jennifer Boyce 2 , Steve Hampton 3 , Joanne Kerbavaz 4 , and
Sarah Mongano 5 ; 1 U.S. Fish and Wildlife Service; 2 National Oceanic and Atmospheric Administration; 3 Office