Rena R. Borkhataria

Additive Effects Of Vertebrate Predators On Insects In A Puerto Rican Coffee Plantation

A variety of studies have established the value of shaded coffee plantations as habitat for birds. While the value of birds as biological controls in coffee has received some attention, the interactions between birds and other predators of insects have not been tested. We used exclosures to examine the effects of vertebrate predators on the arthropods associated with coffee, in particular the coffee leafminer (Leucoptera coffeella) and the flatid planthopper Petrusa epilepsis, in a shaded coffee plantation in Puerto Rico. We used a 2 x 2 factorial design with four treatments: exclusion of birds, lizards, birds and lizards, and control (no exclusion). Abundance of insects > 5 mm increased when birds or both birds and lizards were removed. Birds and lizards had an additive effect for insects < 5 mm and for all insects combined. Coffee leafminers showed a weak response to removal of predators while planthopper abundance increased significantly in the absence of avian predators. Arthropod predators and parasitoids did not differ significantly between treatments. Our findings suggest that vertebrate insectivores have an additive effect on insects in coffee and may help control abundances of some coffee pests. Equally important, we present evidence suggesting that they do not interfere with other known natural enemies of coffee pests.

A Preliminary Model of Wood Stork Population Dynamics in the Southeastern United States

Abstract We modeled population dynamics and extinction probabilities for the endangered Wood Stork (Mycteria americana) using count data from synoptic aerial surveys, annual measures of productivity from throughout the southeastern U.S., and survival data from satellite-tagged juveniles. Using a simple, count-based diffusion approximation approach we were able to quantify an increasing population trend since 1976. High inter-year variability resulted in wide confidence intervals and we could not eliminate the possibility of long-term population decline in spite of recently measured population increases. We also used a stage-based population matrix model to incorporate observed differences in survival rates among age classes. Fledging success, and survival of fledglings, one, and two-year-old birds were estimated using data from the satellite telemetry study. Because the survival rates of three-year-olds and adults are presently unknown, we analyzed population dynamics over a range of these values. Long-term population growth was most sensitive to changes in adult survivorship. This deterministic matrix model indicated that adult survival rates >0.94 were necessary to maintain a growing population, an estimate considerably higher than that observed in the European White Stork (Ciconia ciconia). This study underscores the need for reliable estimates of juvenile and adult survival in Wood Storks, and for a conservation focus on the factors that affect adult survival. It also provides a tool for understanding and projecting potential trajectories of the Wood Stork population in the Southeastern United States.

Temporal Variation in Local Wetland Hydrology Influences Postdispersal Survival of Juvenile Wood Storks (Mycteria americana)

ABSTRACT. Since the 1960s, anthropogenic shifts in the timing and distribution of surface-water flows in the Everglades have pushed back the onset of reproduction in Wood Storks (Mycteria americana). Late nesting increases the probability that juveniles leave the colony during the summer rainy season, when water levels are high and prey animals unavailable. We used satellite telemetry to track firstyear survival of 85 Wood Storks from southern Florida over 4 years. We further evaluated survival in relation to hydrologic and physiologic variables, including water depths, surface-water recession rates, May rainfall, use of wetland habitats, sex, total feather mercury, whiteblood-cell counts, and heterophih:lymphocyte ratios for a subset of 71 birds, using a known-fates model in Program MARK. Juveniles that dispersed from the colony during favorable conditions (surface water depths <25 cm) had a first-year survival rate of 0.37 ± 0.06 (SE), compared with 0.15 ± 0.04 for those that dispersed into unfavorable conditions (depths >25 cm). General hydrologie conditions (favorable vs. unfavorable), wetland habitat use, and white-blood-cell counts were the best predictors of monthly survival, and the strongest effects were associated with the first month postdispersal. Our study is the first to show a relationship between temporally fluctuating hydrologic variables and survival of juvenile Wood Storks, highlighting the need to consider the timing of hydrologic manipulations when managing wetlands for birds. We conclude that human-induced changes in the temporal patterns of hydrology may have important consequences for the phenology and, ultimately, the demography of wetland birds.

Effects of Blackbirds (Agelaius phoenicius) on Stink Bug (Hemiptera: Pentatomidae) Populations, Damage, and Yield in Florida Rice

ABSTRACT Blackbirds are important agricultural pests that can cause major economic losses in a variety of crops. Although birds in other agro-ecosystems may perform biological control services by controlling insect pests, the potential of blackbirds to provide these services in rice had not been evaluated. We used bird exclosures to evaluate the effects of blackbirds on stink bugs in rice and on crop damage and yields in the Everglades Agricultural Area in southern Florida. Experiments were conducted in both the main rice crop and the ratoon crop. We found no difference in the abundance of rice stink bugs (Oebalus spp.) in exclosures vs. controls, indicating that predation by birds did not reduce stink bug populations. Damage to rice by stink bugs (pecky rice) was similar between exclosures and controls, as well. However, bird damage, quantified as the percentage of panicles damaged, differed by as much as an order of magnitude in exclosures vs. controls. Mean damage estimates were 3.5% in the bird exclosures vs. 35.3% in the control for the main crop and 4.5% and 20.5%, respectively, in the exclosures and controls for the ratoon crop. Nonetheless, mean yields did not differ between exclosures and controls. Our results suggest that despite their conspicuous presence, blackbirds have little effect on stink bug populations or rice yield in Florida rice fields.

The relationship of political party affiliation to wildlife conservation attitudes.

Species conservation via the Endangered Species Act is highly politicized, yet few data have been gathered to illustrate the relationship of political party affiliation to species conservation perspectives. We conducted a nationwide public opinion survey and found that Democrats value species conservation more highly than do Republicans, and that Democrats are also more strongly supportive of the Endangered Species Act. Republicans place higher value on property rights than do Democrats, but members of both parties value economic growth as highly as wildlife conservation. The results imply that the Democratic propensity to value species conservation reflects a biocentric perspective that does not bode well for practical conservation efforts. Species conservation will depend upon the success of academicians and progressive political leaders in educating students and members of all parties about the fundamental conflict between economic growth and wildlife conservation.

Testing for Associations between Hematozoa Infection and Mercury in Wading Bird Nestlings

Abstract Several wading bird species in the southeastern US have a history of infection by hematozoa/avian malaria as well as mercury accumulation through their diet, and thus may be exposed to two, generally sublethal, yet chronic, stressors. We analyzed nestling wading birds (n = 171) of varying size and trophic position from the southeastern US, and a smaller sample (n = 23) of older, free-ranging birds, to look for potential interrelationships between infection by hematozoa and mercury (Hg) uptake. Only one nestling was PCR positive for hematozoa (Plasmodium/Haemoproteus) whereas nine (39%) of the older wading birds were positive. Sequencing indicated that both nestling and adult positives were infected with Plasmodium. Given the low infection rate of the nestlings, there was no association between Hg and malaria. The older birds exhibited a possible malaria/Hg association, but it may be confounded by their greater potential exposure period and large-scale movements.

Movements and Habitat Use by Fledgling Wood Storks (Mycteria Americana) Prior to Dispersal from the Natal Colony

Abstract. Activity patterns of fledgling storks (Ciconiidae) during the parental-dependency period are poorly understood for many species, including the Wood Stork (Mycteria americana). Satellite telemetry was used to track the movements of fledgling Wood Storks ( n = 50) from the time they attained minimum flight capabilities until dispersal from the natal colony. Distances traveled, range size, and habitat use by fledgling Wood Storks were quantified for early (prior to the final week before dispersal) and late (the final week before dispersal) predispersal periods and for the entire predis-persal period as a whole. Metrics were compared among three colonies and between two years at a single colony using nonparametric tests. For the entire predispersal period, the mean daily maximum distance of juvenile Wood Storks from their nest was 1.39 ± 0.2 km (median = 0.18 and maximum = 103.13) and the mean cumulative distance moved per day was 2.38 ± 0.28 km (median = 0.45 and maximum = 110.58). Movement distances differed among colonies and between years, while core and total ranges were similar regardless of location. The majority of locations (84%) occurred within colony boundaries, 95% occurred within 1.0 km of the colony and 98% occurred within 3.5 km of the colony. Flight distances did not increase linearly with time and instead followed a Poisson distribution, increasing sharply during the final week before dispersal. Habitat management recommendations for juvenile Wood Storks are to preserve wetland features within a 1.0–3.5 km zone around a colony.

Characterization of Tidally Influenced Wood Stork Foraging Habitats in Georgia

Abstract To characterize tidally influenced Wood Stork foraging habitats, we documented the physical structure and potential prey populations of 17 known (based primarily on satellite telemetry locations) foraging and 20 “alternate” (similar habitat) sites, tidal creeks, in coastal Georgia. The majority of sites contained reaches partially impounded by three landscape features: oyster-shell dams, root/mud dams, or the junction of two or more creeks. Potential prey species, dominated by Fundulus heteroclitus (Mummichog) and shrimp, were highly variable among the tidal habitats but generally occurred in densities (average > 140 individuals/m2) far greater than those observed in an earlier inland Georgia study. There were no differences in potential prey densities between known foraging and alternate sites, confirming that the large salt marsh region of Georgia provides excellent foraging habitat for the regional Wood Stork population.