Zenaida Macroura Research Articles

Mourning Dove Productivity in California during 1992-95: Was It Sufficient to Balance Mortality?

Mourning dove (Zenaida macroura) populations have declined steadily in the western United States since 1966. We investigated the role of recruitment in this long-term problem by studying nesting ecology of mourning doves from March to September 1992-95, in the northern Central Valley, California, USA, We studied nesting doves in blue oak woodlands (Quercus douglasii), willow-cottonwood riparian habitats (Salix spp., Populus fremontii), and commercial walnut, prune, pistachio, and cherry orchards. We used 3,047 nests for our analyses, Doves initiated nests from 14 March to 28 August; nesting season lengths ranged from 105 to 158 days. Only 2-5% of nests remained active after 1 September each year, and latest dates that young fledged ranged from 28 August to 21 September. Mayfield estimates of nest success rates varied inconsistently among study areas; annual success rates ranged from 35-59% for incubation, 49-79% for brooding, and 22-45% for total. Akaike's Information Criteria (AIC) analysis showed that total nest success was higher during years with relatively warm-dry springs (March-May, 1992 and 1994 [35-45% success]) than years with relatively cool-wet springs (1993 and 1995 [22-37% success]). Additionally, AIC analysis showed that fledglings produced/pair and fledglings/nesting attempt were highest during the warm-dry years. Likewise, we recorded more total pairs, nests, and total fledglings, and longer nesting seasons during the warm-dry years. The lower limit of the 95% confidence interval for fledglings produced/pair for all years exceeded the value of 2.5 previously estimated with banding data from 1967-74 as the value required to maintain breeding populations in California. Thus, if our productivity estimates reflected the general population, and annual survival rates had not changed, recruitment should have been adequate to produce an increasing population. Since this was not occurring, managers should complement population surveys with annual banding and harvest surveys to enable thorough examination of the relationships among survival, productivity, and abundance.

Area Requirements of Grassland Birds: A Regional Perspective

AbstractArea requirements of grassland birds have not been studied except in tallgrass prairie. We studied the relation between both species-occurrence and density and patch size by conducting 699 fixed-radius point counts of 15 bird species on 303 restored grassland areas in nine counties in four northern Great Plains states. Northern Harrier (Circus cyaneus), Sedge Wren (Cistothorus platensis), Clay-colored Sparrow (Spizella pallida), Grasshopper Sparrow (Ammodramus savannarum), Baird's Sparrow (Ammodramus bairdii), Le Conte's Sparrow (Ammodramus leconteii), and Bobolink (Dolichonyx oryzivorus) were shown to favor larger grassland patches in one or more counties. Evidence of area sensitivity was weak or ambivalent for Eastern Kingbird (Tyrannus tyrannus), Common Yellowthroat (Geothlypis trichas), Savannah Sparrow (Passerculus sandwichensis), and Western Meadowlark (Sturnella neglecta). Red-winged Blackbirds (Agelaius phoeniceus) preferred larger patches in some counties, and smaller patches in others. Mourning Doves (Zenaida macroura) and Brown- headed Cowbirds (Molothrus ater) tended to favor smaller grassland patches. Three species showed greater area sensitivity in counties where each species was more common. Five species demonstrated some spatial pattern of area sensitivity, either north to south or east to west. This study demonstrates the importance of replication in space; results from one area may not apply to others because of differences in study design, analytical methods, location relative to range of the species, and surrounding landscapes.

Factors Influencing Mourning Dove Nest Success in CRP Fields

Mourning doves (Zenaida macroura) nest primarily in trees. However, ground nesting is prevalent in the Great Plains region where mourning dove numbers have increased since the mid 1980s when the Conservation Reserve Program (CRP) was initiated. We monitored mourning dove nest success in CRP fields in Kansas during 1994 and 1995 to determine if that habitat could be a source for the increased numbers. Mourning dove nest success averaged 56% (n = 90) in our CRP fields. Daily nest survival rates in CRP fields were associated positively with height of live vegetation (P = 0.011) and negatively with percent grass cover (P = 0.001) and percent live vegetation cover (P = 0.005). Management practices that produce sparse overall cover but tall vegetation height may increase mourning dove nest success in CRP fields.

Blood plasma chemistries from wild mourning doves held in captivity.

Despite the extensive amount of research conducted on mourning doves (Zenaida macroura), no biochemical reference values exist for this species. Our objective, therefore, was to establish base line clinical chemistry reference values for mourning doves to assist with establishing clinical diagnoses. Wild mourning doves were captured 19 March 1996 to 8 August 1996, and 6 February 1998 to 12 May 1998; blood samples were collected from 382 mourning doves. Plasma biochemical values were established for glucose, sodium, potassium, chloride, enzymatic CO2, albumin, total protein, globulin, calcium, phosphorus, cholesterol, magnesium, aspartate aminotransferase (AST), gamma glutamyl transferase (GGT), lactate dehydrogenase (LDH), and uric acid. These reference values are invaluable for determining diagnosis of diseases of the gastrointestinal, hepatic, renal, cardiovascular, musculoskeletal, and endocrine systems.

Records of ticks (Acari: Ixodidae) parasitizing birds (Aves) in Rhode Island, USA

Incidental to studies on Lyme disease in Rhode Island, a total of 531 birds represented by 68 species, was collected and examined for the presence of ticks and other ectoparasites. Of these birds, a total of 230, comprising 36 species, harbored ticks in the pre-adult stage. In all 1,174 ticks were collected. Tick burden ranged from 1 to 76 specimens per bird. Ixodes scapularis Say was the species most commonly encountered (n=1,005). Other species included Haemaphysalis leporispalustris (Packard) (n=69), Ixodes muris Bishopp and Smith (n=57), Ixodes dentatus Marx (n=23), Dermacentor variabilis (Say) (n=2), and Ixodes cookei Packard (n=1). Of the 36 species of birds harboring ticks, only 3 species, the Common Yellowthroat Geothylypsis trichas (L.), Veery Catharus fuscescens (Stephens) and Carolina Wren Thryothorus ludovicianus (Lathum), served as hosts to 90% of the ticks collected. However, the small number of birds collected for several of the species represented precludes statistical comparison of many species. Dermacentor variabilis nymphs on an American Redstart (Setophaga ruticilla L.) and a Mourning Dove [Zenaida macroura (L.)] as well as an I. cookei larva on a Gray Catbird [Dumetella carolinensis (L.)] constitute new host records. This study surveys for the first time avian hosts for ticks within Rhode Island, and demonstrates that birds play an important role in the life cycle of ticks.

HOME RANGE CHARACTERISTICS OF MALE COOPER'S HAWKS IN AN URBAN ENVIRONMENT

We monitored the movements of nine radio-tagged, adult, male Cooper's Hawks (Accipiter cooperii) in adjacent home ranges during the breeding seasons of 1996 or 1997 in Tucson, Arizona, to ascertain the sizes and degree of overlap of home ranges, and to assess habitat selection at two spatial scales. Size of home ranges differed among hawks (13.3–130.6 ha), but the average was small [65.5 ha ± 40.7 (SD)] compared to the size of home ranges reported for Cooper's Hawks in the literature. Home range size generally decreased with the number of years that a hawk had lived on its breeding territory. Only one pair of home ranges overlapped each other; overlap of one home range on the other in this pair was 14.2% and 10.6%. Proportions of land-use categories in home ranges varied widely among hawks, and suggested that the hawks did not select their home ranges on the basis of the categories we examined. Patterns of habitat use inside individual home ranges suggested that male hawks hunted primarily in the environments that surrounded their nests. Cooper's Hawks in Tucson feed primarily on doves [Mourning Doves (Zenaida macroura), Inca Doves (Columbina inca), and White-winged Doves (Zenaida asiatica)], and we speculate that the abundance of doves throughout Tucson allowed the hawks to hunt successfully in several urban environments. We also speculate that Cooper's Hawks in Tucson have relatively small home ranges because they do not need to range far from their nests to find food.

Telling Western Stories: From Buffalo Bill to Larry McMurtry

What has the western of literature and film contributed to American culture? Richard Etulain, the leading cultural historian of the West, answers that question by tracing four distinct storytelling traditions and exploring the indelible images each has left in the public's mind over the past 125 years. Our images of cowboys, lawmen, outlaws, and Indians come from a collage of sources, including Buffalo Bill, Frederick Jackson Turner, Calamity Jane, Mary Hallock Foote, Geronimo, Mourning Dove, Owen Wister, Zane Grey, Walter Noble Burns, John Ford, Louis L'Amour, Wallace Stegner, Patricia Nelson Limerick, Leslie Marmon Silko, and Larry McMurtry. Etulain begins with the dominant image conveyed in Wild West shows and dime novels of the late nineteenth century--the West as a place of adventure and danger. In the early twentieth century stories by women and Indians appeared, but they were soon overlooked and not rediscovered until the 1970s. The period from the 1920s to the 1950s represents the classic era of western movies and novels--of cavalry charges to save the day and heroes in white hats. But since the 1960s a counter story has emerged, one of ambiguity and complexity that often turned upside down our notions about what really mattered in how we look at the West. Etulain carefully explores why stories of the frontier and American West still rival those of the American Civil War as the country's most popular tales, and he shows how narratives that persisted relatively unchanged for a century have moved in notable new directions since the 1960s.

Inhibiting ventilatory evaporation produces an adaptive increase in cutaneous evaporation in mourning doves Zenaida macroura.

We tested the hypothesis that birds can rapidly change the conductance of water vapor at the skin surface in response to a changing need for evaporative heat loss. Mourning doves (Zenaida macroura) were placed in a two-compartment chamber separating the head from the rest of the body. The rate of cutaneous evaporation was measured in response to dry ventilatory inflow at three ambient temperatures and in response to vapor-saturated ventilatory inflow at two ambient temperatures. At 35 degrees C, cutaneous evaporation increased by 72 % when evaporative water loss from the mouth was prevented, but no increase was observed at 45 degrees C. For both dry and vapor-saturated treatments, cutaneous evaporation increased significantly with increased ambient temperature. Changes in skin temperature made only a minor contribution to any observed increase in cutaneous evaporation. This indicates that Z. macroura can effect rapid adjustment of evaporative conductance at the skin in response to acute change in thermoregulatory demand.

Avian serology in a St. Louis encephalitis epicenter before, during, and after a widespread epidemic in south Florida, USA.

Blood and serum from 3,915 wild and domestic birds (2,590 resident, 139 migrant, and 1,186 captive), representing 56 species collected in central Florida from 1989 through 1997, were analyzed for evidence of St. Louis encephalitis (SLE) virus transmission. All sera were tested for SLE hemagglutination inhibition (HI) antibody. Selected sera and bloods were tested for SLE neutralizing (NT) antibody and virus. The reproductive success of resident birds was highest from 1990-1992 and lowest from 1994-1997. Transmission of SLE to resident birds, especially mourning doves (Zenaida macroura), peaked during the summer of 1990, a year during which a widespread SLE epidemic was recorded in central Florida. The SLE antibody-positive resident birds 1st appeared during September of the epidemic year. Some SLE, HI antibody-positive resident birds were captured throughout 1991, but only 5% were yearlings, compared with 36% in 1990. By 1993, wild resident birds expressing HI and NT antibodies to SLE had nearly disappeared. None of the migrant birds tested were SLE-positive. Sentinel chickens maintained in Indian River County during the epidemic year seroconverted to SLE starting in early July with peak seroconversion rates in August, September, and October. High (> or = 50%) SLE seroconversion rates in sentinel chickens preceded those in wild birds by 10 wk and preceded peak human SLE transmission by at least 8 wk. Major SLE epidemics in south Florida depend on abundant wild bird populations, especially during the amplification phase of the transmission cycle. We propose that hard winter freezes along the temperature-subtropical climatic zone interface in central Florida, at approximately 27 degrees 30' North Latitude, opens foraging and nesting habitats for ground-feeding birds, resulting in high reproductive success and an abundance of seronegative individuals that rapidly amplify the SLE later in the year.

Molt of After-Hatching-Year Mourning Doves

We studied molts and plumages of 28 captive and 112 wild after-hatching-year (AHY) mourning doves (Zenaida macroura) in eastcentral Alabama to better understand the timing of, processes involved in, and factors affecting annual molt Captive doves were paired and reproduced in outdoor flight pens exposed to natural photoperiod and weather. We evaluated molt progression in captive doves at 28-day intervals. During the weeks we examined captive doves, we also trapped and evaluated molt in wild doves For captive and wild doves, time (sampling period) was the only consistent factor affecting inolt (P < 0.001). Body molt of captive and wild doves began in August, peaked in October, and ended by December Tail feather (rectrix) molt coincided with body molt in captive but not wild doves. Molt of primary feathers (remiges) in both groups followed an orderly outward sequence and was initiated by May and completed by December. The complete body molt initiated in late summer resulted in the drab plumage typical of mourning doves in winter. Males had visible olive-colored tips on the crown, hind neck, and, to a lesser degree, the chest. Gradual deterioration of the margins of these feathers revealed the more colorfnl breeding plumage by late winter and early spring Although the winter plumage of females also was olive-tipped it did not contrast enough with the spring plumage to cause a noticeable seasonal color change. Apparently, AHY mourning doves compensate for molt-breeding overiap by spreading wing molt over ≥6 months by initiating annual body head and tail molt when food is abundant in autumn, and by timing the majority of molt concurrent with, or following, the final clutch of the season, just prior to the stressors of winter.

Mixedblood Messages: Literature, Film, Family, Place

In this challenging and often humorous book, Louis Owens examines issues of identity and relationship to the environment as depicted in literature and film and as embodied in his own mixedblood roots in family and land. Powerful social and historical forces, he maintains, conspire to colonize literature and film by and about Native Americans into a safe Indian that will contain and neutralize Indians. Countering this colonial Territory is what Owens defines as Frontier, a dynamic, uncontainable, multi-directional space within which cultures meet and even merge.Owens offers new insights into the works of writers ranging from John Rollin Ridge, Mourning Dove, and D'Arcy McNickle to N. Scott Momaday, Leslie Silko, James Welch, and Gerald Vizenor. In his analysis of Indians in film he scrutinizes distortions of Indians as victims or vanishing Americans in a series of John Wayne movies and in the politically correct but false gestures of the more recent Dances With Wolves. As Owens moves through his personal landscape in Oklahoma, Mississippi, California, and New Mexico, he questions how human beings collectively can alter their disastrous relationship with the natural world before they destroy it. He challenges all of us to articulate, through literature and other means, messages of personal and environmental - as well as cultural - survival, and to explore and share these messages by writing and reading across cultural boundaries.

Effects of Implanted Radiotransmitters on Captive Mourning Doves

Previous mourning dove (Zenaida macroura) telemetry studies using transmitter glue attachment have found the technique to be relatively short term (<10 weeks), and that transmitter harnesses possibly have deleterious effects on doves. To improve attachment methods, we developed and refined surgical techniques for implanting subcutaneous and intra-abdominal radiotransmitters with external whip antennas in mourning doves, and we determined physiological and pathological responses to the transmitter implants. We used a captive colony of 200 wild-trapped mourning doves to develop and test procedures for subcutaneous implants (SC1), subcutaneous surgeries without implants (SC2), intra-abdominal implants (IA1), intra-abdominal sur- geries without implants (IA2), and a control group without surgeries or implants (CNT); 20 males and 20 females were assigned to each experimental group. Surgeries for IA1 took less time (3.58 t 0.17 min; i? + SE; P < 0.001) than SC1 surgeries (4.36 ? 0.12 min). Heterophil:lymphocyte ratios showed that IA1 and IA2 doves had higher (P = 0.024) posttreatment changes compared with SC1, SC2, or CNT groups. At 4-6 days postsurgery, 153 of 160 (95.6%) doves with surgical treatments showed closed or healed surgical sites with no complications. At 14 days posttreatment, 34 (87%) SC1 implants were located in the thoracic inlet. Gross necropsy findings at 10 weeks postsurgery found that 36 of 39 (92%) SC1 and 36 of 39 (92%) IA1 implants showed little or no tissue response to the implants. Functioning transmitters began failing 2 weeks posttreat- ment, and 85% were not working at 10 weeks posttreatment. Our data suggest subcutaneous implants with external antennas were a better alternative compared to intra-abdominal implants with external antennas, but further testing is needed to compare subcutaneous implants to conventional attachment techniques.

A Risk Assessment for Consumers of Mourning Doves

Recreational and subsistence hunters and anglers consume a wide range of species, including birds, mammals, fish and shellfish, some of which represent significant exposure pathways for environmental toxic agents. This study focuses on the Department of Energy's (DOE'S) Savannah River Site (SRS), a former nuclear weapons production facility in South Carolina. The potential risk of contaminant intake from consuming mourning doves (Zenaida macroura), the most popular United States game bird, was examined under various risk scenarios. For all of these scenarios we used the mean tissue concentration of six metals (lead, mercury, cadmium, selenium, chromium, manganese) and radiocesium, in doves collected on and near SRS. We also estimated risk to a child consuming doves that had the maximum contaminant level. We used the cancer slope factor for radiocesium, the Environmental Protection Agencies UptakeBiokinetic model for lead, and published reference doses for the other metals. As a result of our risk assessments we recommend management of water levels in contaminated reservoirs so that lake bed sediments are not exposed to use by gamebirds and other terrestrial wildlife. Particularly, measures should be taken to insure that the hunting public does not have access to such a site. Our data also indicate that doves on popular hunting areas are exposed to excess lead, suggesting that banning lead shot for doves, as has been done for waterfowl, is desirable.

A risk assessment for consumers of mourning doves.

Recreational and subsistence hunters and anglers consume a wide range of species, including birds, mammals, fish and shellfish, some of which represent significant exposure pathways for environmental toxic agents. This study focuses on the Department of Energy's (DOE's) Savannah River Site (SRS), a former nuclear weapons production facility in South Carolina. The potential risk of contaminant intake from consuming mourning doves (Zenaida macroura), the most popular United States game bird, was examined under various risk scenarios. For all of these scenarios we used the mean tissue concentration of six metals (lead, mercury, cadmium, selenium, chromium, manganese) and radiocesium, in doves collected on and near SRS. We also estimated risk to a child consuming doves that had the maximum contaminant level. We used the cancer slope factor for radiocesium, the Environmental Protection Agencies Uptake/Biokinetic model for lead, and published reference doses for the other metals. As a result of our risk assessments we recommend management of water levels in contaminated reservoirs so that lake bed sediments are not exposed to use by gamebirds and other terrestrial wildlife. Particularly, measures should be taken to insure that the hunting public does not have access to such a site. Our data also indicate that doves on popular hunting areas are exposed to excess lead, suggesting that banning lead shot for doves, as has been done for waterfowl, is desirable.

Management of fat reserves in tufted titmiceBaelophus bicolorin relation to risk of predation

Fat reserves are an important energy source for animals wintering in temperate zones. Long nights, low ambient temperature and often unpredictable food all increase the probability of death from starvation, and to survive, animals carry energy reserves as fat. Based on the assumption that extra weight makes birds more vulnerable to diurnal predators, it has been hypothesized that predation risk places an upper limit on avian fat reserves. The hypothesis leads to the prediction that birds should decrease their mass in response to increased risk of predation. We tested this prediction with a resident species, the tufted titmouse,Baelophus bicolor. During a 3-day period, we presented a taxidermic mount of a sharp-shinned hawk,Accipiter striatus(predator treatment) or a mourning dove,Zenaida macroura(control treatment) to seven titmice housed individually with food ad libitum. Even though vigilance and delay in time to resume foraging were significantly higher after exposure to the hawk model, the body mass of titmice after exposure to the hawk increased rather than decreased, a result opposite to that predicted. In particular, the birds significantly increased their evening body mass and mean daily mass gain during the treatment period. Our results suggest that risk-dependent foraging appears to regulate avian body fat reserves by limiting foraging time. When food is unlimited, as in our experiment, birds may be able to obtain high energy reserves even while maintaining intense vigilance for predators, and under such conditions, the energetic costs of flying may control upper level energy reserves.

Radiocesium in Mourning Doves: Effects of a Contaminated Reservoir Drawdown and Risk to Human Consumers

From September 1991 through January 1995, partial drawdown of a 1,130-ha U.S. Department of Energy reactor cooling reservoir (Par Pond) in South Carolina exposed sediments contaminated by low-level radiocesium ( 137 Cs). These exposed sediments were designated as a U.S. Environmental Protection Agency (EPA) superfund site. Whole-body and muscle concentrations of 137 Cs in mourning doves (Zenaida macroura) collected from Par Pond in 1992 and 1993 were 2-3 orders of magnitude higher than in doves from nearby public dove-hunting fields located 12 and 32 km away. Only 1 of 102 Par Pond doves exceeded the European Economic Community limit of 0.60 Becquerels (Bq) 137 Cs/g for fresh meat. A human risk analysis based on consumption of doves at the observed maximum of muscle 137 Cs concentration (0.82 Bq/g wet mass) indicated no more than 41 doves could be consumed by an individual per year at that level before the EPA threshold for action on a superfund site would be exceeded (i.e., further site characterization, possible remedial action). Levels of whole-body 137 Cs in doves from Par Pond declined by >75% from 1992 through 1994. Pokeweed (Phytolacca americana) seeds, the dominant food of doves foraging on the exposed lake bed, likewise declined (>90%) in 137 Cs content over the period. We noted subtle annual changes in the diets of doves that likely contributed to reduced rates of 137 Cs ingestion as the drawdown progressed. Doves differed by age class in their food intake and selection, and immature doves showed higher levels of ingesta 137 Cs. However, age classes did not differ in whole-body 137 Cs (P = 0.156) or muscle 137 Cs (P = 0.181). Dove whole-body 137 cs was a good predictor (r2 = 0.94) of muscle 137 Cs, and thus provides the opportunity to estimate levels of 137 Cs in edible muscle without destructive sampling by simply subjecting live-captured birds to whole-body determination of 137 Cs content. The radiological consequences of a long-term drawdown or complete draining of such a reservoir are not clear.

Population Demographics of Two Local South Carolina Mourning Dove Populations

The mourning dove (Zenaida macroura) call-count index had a significant (P 2,300 doves and examined >6.000 individuals during harvest bag checks. An age-specific band recovery model with time- and area-specific recovery rates, and constant survival rates, was chosen for estimation via Akaike's Information Criterion (AIC), likelihood ratio, and goodness-of-fit eriteria. After-hatching-year (AHY) annual survival rate was 0.359 (SE = 0.056), and batching-year (HY) annual survival rate was 0.118 (SE = 0.042). Average estimated recruitment per adult female into the prehunting season population was 3.40 (SE = 1.25) and 2.32 (SE = 0.46) for the 2 study areas. Our movement data support earlier hypotheses of nonmigratory breeding and harvested populations in South Carolina. Low survival rates and estimated population growth rate in the study areas may be representative only of small-scale areas that are heavily managed for dove hunting. Source-sink theory was used to develop a model of region-wide populations that is composed of source areas with positive growth rates and sink areas of declining growth. We suggest management of mourning doves in the Southeast might benefit from improved understanding of local population dynamics, as opposed to regional-scale population demographics.

Metal Levels in Mourning Doves from South Carolina: Potential Hazards to Doves and Hunters

Most game birds are found in lower trophic levels, but since such birds are harvested and consumed by humans, there is a particular need to assess their contaminant levels. In this paper, we report concentrations of mercury, lead, cadmium, selenium, manganese, and chromium in the breast feathers, liver, and muscle of mourning doves (Zenaida macroura) collected at a partially drawn-down, contaminated reactor-cooling reservoir (Par Pond) on the Department of Energy's Savannah River Site in South Carolina and at nearby agricultural fields managed as dove hunting areas. We test the hypothesis that the levels in doves are not harmful to either dove populations or humans. We also tested the simultaneous effects of collection location, year (1992, 1993), and dove age-class (hatch-year vs after hatch-year) on heavy metal and selenium levels. For all three tissues, mercury levels were nondetectable at all locations. Lead was highest in tissues from agricultural fields with prior histories of dove hunting activities. Doves at those fields were likely ingesting lead shot to a greater degree than at the recently drawn-down reservoir which was closed to public access and hunting. For other metals, Par Pond doves had equally high or higher tissue levels. For all metals, levels in doves from South Carolina were generally within the lower range of those reported in the literature, suggesting that these metals were likely to pose no health problems to these doves. Except for lead and selenium, metal levels in dove muscle that we observed were well below reference metal doses established for human intake. Lead and selenium, at the levels described here, would only be a problem if a child (not an adult) ate 120 g of dove meat every day of the year. Thus, we conclude that meat from these doves, if consumed by hunters, would not pose a risk.

Potential Effects of Environmental Contaminants on Recovery of the Aplomado Falcon in South Texas

Efforts to reintroduce the aplomado falcon (Falco femoralis) into its former range in the southern part of Texas began in 1977. Not until 1993, however, were a significant number (26) of fledgling aplomado falcons released. The first nesting pair of aplomado falcons was reported near the Brownsville Ship Channel during 1995. Because of a long history of pesticide use in the Lower Rio Grande Valley, during 1993-94 we investigated the accumulation of environmental contaminants in plasma of aplomado falcons released at the Laguna Atascosa National Wildlife Refuge. We also assessed the potential contribution of typical prey species to aplomado falcon contaminant burdens. Organochlorine pesticides and PCBs were below detection limits (wet wt basis) in plasma; however, some organochlorines including 1.75 and 1.41 μg/g p,p'-DDE, and 0.49 and 1.52 μg/g total PCBs were detected in addled eggs collected in 1995 and 1996. Mercury also was detected at 1.5 and 4.1 μg/g dry weight in the addled eggs collected in 1995 and 1996. We detected DDE (range 0.02-0.25 μg/g) in carcasses of potential prey of the aplomado falcon. Trace metals also were detected in potential prey at levels which are not of concern, except for Hg, which was high in a few meadowlarks. Low levels of DDE and most trace metals in potential prey, including mourning doves (Zenaida macroura) and eastern meadowlarks (Sturnella magna), are not likely to result in adverse effects on the aplomado falcon in the Lower Rio Grande Valley. However, elevated Hg residues in meadowlarks (in a few cases) and potentially higher DDE levels in other prey species such as the great-tailed grackle (Quiscalus mexicanus) could result in negative effects on reproduction and survival of some aplomado falcons in south Texas.

Assessing the Hazard to Granivorous Birds Feeding on Chemically Treated Seeds

Current methods for evaluating hazards to seed-eating birds are based on estimated exposure per unit area and assume that birds ingest all of the chemical on a treated seed. In an earlier study, however, it was determined that red-winged blackbirds removed only about 15% of an insecticidal treatment applied to individual rice seeds. Here, we extend those -ndings by examining the seed-handling behavior of four granivorous bird species exposed to millet, rice, sunNower and sorghum treated with imidacloprid. Mourning doves (Zenaida macroura L.) swallowed the seed whole. House -nches (Carpodacus mexicanus Mue ller), red-winged blackbirds (Agelaius phoeniceus L.) and boat-tailed grackles (Quiscalus major Vieillot) discarded the seed hulls, however, and removed only 15E40% of the initial chemical treatment. Residues on seed hulls decreased as handling time increased. SunNowers had the lowest residues because birds repeatedly handled the hull to remove bits of the oily kernel. These results suggest that avian hazard assessment methods should incorporate species-typical seed-handling behavior to assess more accurately birdsI exposure to chemicals on di†erent types of seed.