Clinton W. Jeske

Spatial modeling of the geographic distribution of wildlife populations: a case study in the lower Mississippi River region

Abstract A geographic information system (GIS)-based spatial modeling approach was developed to study environmental and land use impacts on the geographic distribution of wintering northern pintails ( Anas acuta ) in the Lower Mississippi River region. Pintails were fitted with backpack radio transmitter packages at Catahoula Lake, LA, in October 1992–1994 and located weekly through the following March. Pintail survey data were converted into a digital database in ARC/INFO GIS format and integrated with environmental GIS data through a customized modeling interface. The study verified the relationship between pintail distributions and major environmental factors and developed a conceptual relation model. Visualization-based spatial simulations were used to display the movement patterns of specific population groups under spatial and temporal constraints. The spatial modeling helped understand the seasonal movement patterns of pintails in relation to their habitat usage in Arkansas and southwestern Louisiana for wintering and interchange situations among population groups wintering in Texas and southeastern Louisiana.

Comparison and Assessment of Aerial and Ground Estimates of Waterbird Colonies

Abstract Aerial surveys are often used to quantify sizes of waterbird colonies; however, these surveys would benefit from a better understanding of associated biases. We compared estimates of breeding pairs of waterbirds, in colonies across southern Louisiana, USA, made from the ground, fixed-wing aircraft, and a helicopter. We used a marked-subsample method for ground-counting colonies to obtain estimates of error and visibility bias. We made comparisons over 2 sampling periods: 1) surveys conducted on the same colonies using all 3 methods during 3–11 May 2005 and 2) an expanded fixed-wing and ground-survey comparison conducted over 4 periods (May and Jun, 2004–2005). Estimates from fixed-wing aircraft were approximately 65% higher than those from ground counts for overall estimated number of breeding pairs and for both dark and white-plumaged species. The coefficient of determination between estimates based on ground and fixed-wing aircraft was ≤0.40 for most species, and based on the assumption that estimates from the ground were closer to the true count, fixed-wing aerial surveys appeared to overestimate numbers of nesting birds of some species; this bias often increased with the size of the colony. Unlike estimates from fixed-wing aircraft, numbers of nesting pairs made from ground and helicopter surveys were very similar for all species we observed. Ground counts by one observer resulted in underestimated number of breeding pairs by 20% on average. The marked-subsample method provided an estimate of the number of missed nests as well as an estimate of precision. These estimates represent a major advantage of marked-subsample ground counts over aerial methods; however, ground counts are difficult in large or remote colonies. Helicopter surveys and ground counts provide less biased, more precise estimates of breeding pairs than do surveys made from fixed-wing aircraft. We recommend managers employ ground counts using double observers for surveying waterbird colonies when feasible. Fixed-wing aerial surveys may be suitable to determine colony activity and composition of common waterbird species. The most appropriate combination of survey approaches will be based on the need for precise and unbiased estimates, balanced with financial and logistical constraints.

Relationship of Body Condition to Survival of Mallards in San Luis Valley, Colorado

Because body condition can influence survival probabilities in waterfowl, our objective was to determine if winter body condition was related to survival of mallards (Anas platyrhynchos). We obtained body mass and condition indices from mallards captured in southern Colorado from December through March 1986-87, 1987-88, and 1988-89. We collected waterfowl carcasses and wings from January through April 1987-89. In 1987, 1988, and 1989, we recovered 229, 4,193, and 1,663 mallard carcasses, respectively. Avian cholera (Pasteurella multocida), a source of mortality in all years, was prevalent in 1988. Starvation (ulna lipid levels <5%) was more prevalent (P < 0.01) among banded mallards than among unbanded mallards. We used logistic regression to assess relationships between condition at time of banding and whether a bird was found dead within 4 months after capture, shot by hunters the subsequent fall, recaptured 1 year later, or of unknown fate. In 1987, there was a relationship between recaptures and condition (P = 0.03), but no relationship between other status categories and condition. There were no relationships between status and condition in 1988. In 1989, only band recoveries from birds found dead were available for analysis; there was no relationship between condition at banding and whether a bird was found dead (P = 0.19). Waterfowl susceptibility to avian cholera may be unrelated to body condition; therefore, avian cholera mortality may have masked relationships among other mortality causes and condition. J. WILDL. MANAGE. 58(4):787-793

Metabolizable energy in Chinese tallow fruit for Yellow-rumped Warblers, Northern Cardinals, and American Robins

Abstract The invasive exotic Chinese tallow tree (Triadica sebifera) produces an abundant fruit crop, which is primarily bird-dispersed. The fruit pulp of tallow is lipid-rich, high in saturated fatty acids, and consumed by many bird species. Long-chained fatty acids can be difficult for many birds to digest and we investigated the ability of tallow consumers to assimilate energy in the pulp. We used the total collection method and compared apparent metabolizable energy (AME) of tallow fruit for three species of birds with differing fruit composition in their natural diets. All birds exhibited nitrogen deficits and lost body mass during the trials. Northern Cardinals (Cardinalis cardinalis) lost more mass (8.73%/day) than Yellow-rumped Warblers (Dendroica coronata) (5.29%/day) and American Robins (Turdus migratorius) (5.48%/day), and had larger nitrogen deficits (−120.1 mg N/g diet) than both species as well (−36.4 mg N/g diet and −68.9 mg N/g diet, respectively). Food intake relative to metabolic body mass was highest in Yellow-rumped Warblers (0.70 g-dry/g0.75·day). Northern Cardinal and American Robin food intake was lower and did not differ from each other (both species: 0.13 g-dry/g0.75·day). Nitrogen corrected values of AME were used to make species comparisons. Yellow-rumped-Warblers exhibited the highest values of AME (30.00 kJ/g), followed by American Robins (23.90 kJ/g), and Northern Cardinals (14.34 kJ/g). We suggest tallow may be an important winter food source for Yellow-rumped Warblers where their ranges overlap.

Potential Use of Weather Radar to Study Movements of Wintering Waterfowl

ABSTRACT To protect and restore wintering waterfowl habitat, managers require knowledge of routine wintering waterfowl movements and habitat use. During preliminary screening of Doppler weather radar data we observed biological movements consistent with routine foraging flights of wintering waterfowl known to occur near Lacassine National Wildlife Refuge (NWR), Louisiana. During the winters of 2004–2005 and 2005–2006, we conducted field surveys to identify the source of the radar echoes emanating from Lacassine NWR. We compared field data to weather radar reflectivity data. Spatial and temporal patterns consistent with foraging flight movements appeared in weather radar data on all dates of field surveys. Dabbling ducks were the dominant taxa flying within the radar beam during the foraging flight period. Using linear regression, we found a positive log-linear relationship between average radar reflectivity (Z) and number of birds detected over the study area (P < 0.001, r2 = 0.62, n = 40). Ground observations and the statistically significant relationship between radar data and field data confirm that Doppler weather radar recorded the foraging flights of dabbling ducks. Weather radars may be effective tools for wintering waterfowl management because they provide broad-scale views of both diurnal and nocturnal movements. In addition, an extensive data archive enables the study of wintering waterfowl response to habitat loss, agricultural practices, wetland restoration, and other research questions that require multiple years of data.

Short-Term Effects of Hurricane Disturbance on Food Availability for Migrant Songbirds During Autumn Stopover

Understanding the consequences of hurricanes on the food resources available to neotropicalnearctic migrant songbirds may provide important insight into the effects of hurricanes on migratory populations. During autumn migration 2006 we investigated the foraging ecology of two species of insectivorous migrants, Blue-gray Gnatcatcher (Polioptila caerulea) and Yellow Warbler (Dendroica petechia), and the availability of their foraging substrates and arthropod food resources in two coastal forests in western Louisiana, which were impacted to different degrees by Hurricane Rita in autumn 2005. Both migrant species attacked prey on bark substrates significantly more frequently, and on live foliage less frequently, in severely damaged forest than in lightly damaged forest (χ2 tests, P < 0.05). However, both species attacked prey on bark less than expected given its availability (i.e., migrants avoided bark), and attacked prey on live foliage more than expected given its availability (i.e., migrants selected live foliage), in severely damaged forest (χ2 tests, P < 0.03). Branch-clipping revealed that arthropod biomass on live hackberry (Celtis laevigata) and sweet acacia (Acacia farnesiana) branches was significantly higher in severely damaged forest than in lightly damaged forest (Mann-Whitney test, P < 0.01). However, because live foliage was significantly less available in severely damaged forest, overall food availability for migrants was lower in severely damaged forest than in lightly damaged forest. Migrant use of, and arthropod biomass on, bark and live-foliage substrates were thus dependent on the availability of those substrates, which differed between sites as a result of hurricane-related habitat disturbance. These results demonstrate that severe hurricane disturbance reduces food availability for insectivorous songbirds during migratory stopover by reducing the availability of preferred foraging substrates.

Estimating Shorebird Populations During Spring Stopover in Rice Fields of the Louisiana and Texas Gulf Coastal Plain

Abstract.— Migrating shorebird populations using approximately 2% of Louisiana and Texas Gulf Coastal rice fields were surveyed during spring migration (March–May of 1997 and 1998) using biweekly stratified random surveys conducted at 50 roadside survey points and approximately 30,000 shorebirds were observed. Shorebird counts were extrapolated and almost 1.4 million birds in 1997 and over 1.6 million birds of 31 species in 1998 were estimated to use rice field habitat for stopover sites in Louisiana and Texas. Greater than 50% of the estimated North American populations were estimated to use rice field habitats for five species, including a species of concern, Buff-breasted Sandpiper (Tryngites subruficollis) at 187%. Because of predictability of suitable rice field habitat acreage, timing of field preparation and water availability, coastal rice prairies are identified as critical spring migration stopover sites.

Ulnar Lipid as an Indicator of Depleted Fat Reserves in Mallards

We wanted to determine if ulnar lipid content of mallards (Anas platyrhynchos) reflected total body lipid, because many scavenged waterfowl carcasses are only represented by wings. Consequently, we euthanized 12 mallards at various stages of starvation to quantify the relationship. Percent ulnar lipid remained constant when total body fat was ≥5%, but ulnar lipid was quickly catabolized when body fat was <5%. With these criteria, we examined ulnar lipid content from 295 mallard carcasses found during the winters of 1987 and 1988 in the San Luis Valley, Colorado. Ulnar lipid did not differ (P=0.83) between years (x=31.0%) for mallards with ulnar lipid levels ≥5%. Females had less (P=0.02) ulnar lipid (x=0.64 g) than males (x=0.74 g) because of their relatively smaller ulnae

Home-Range Size and Site Tenacity of Overwintering Le Conte's Sparrows in a Fire Managed Prairie

Abstract We evaluated home-range size and site tenacity of Le Contes Sparrows (Ammodramus lecontii) during winter 2002–2003 at Brazoria National Wildlife Refuge, Texas. Twenty-six wintering Le Contes Sparrows were radiomarked in 1- and 2-year post-burn units, and monitored for ∼10 days. Additionally, 1-ha plots on each 1-, 2- and 3-year (n  =  15) post-burn units were flush-netted once monthly. Telemetry results indicated Le Contes Sparrows were sedentary during winter with a 50% probability mean home-range of 2.41 ha (72% < 1 ha) and a 95% probability mean home range of 10.31 ha (44% < 1 ha and 55% < 1.5 ha). Home-range size did not differ between post-burn year 1 and 2 (P  =  0.227). Le Contes Sparrows appeared to exhibit a behavioral response to flush-netting (P < 0.001) with estimated capture probability of 0.462 and recapture probability of 0.056. Our findings suggest Le Contes Sparrows remain fairly sedentary throughout the winter.

Prevalence of a potentially lethal parasite of wading birds in natural and agricultural wetlands in south Louisiana

Abstract Gambusia affinis (Western Mosquitofish) were sampled from 18 sites representing marsh, forested wetlands, and agricultural wetlands in south Louisiana to determine distribution and infection parameters of Eustrongylides ignotus, a potentially lethal nematode parasite of wading birds, (n = 400 per site). Overall, prevalence of infection was 0.3%, with significantly higher prevalence in agricultural wetlands than in marshes or swamps. Our findings are similar to work in Florida suggesting parasite prevalence is higher in disturbed wetlands, and suggest that birds foraging in crayfish ponds and rice fields may be at increased risk of exposure.