J. Michael Reed

Behavioural constraints and conservation biology: Conspecific attraction and recruitment

Wildlife managers have devoted considerable time and research to determine how animals judge the suitability and quality of their habitat. These analyses typically center on habitat characteristics and often produce equivocal results. An additional method of habitat assessment is to examine the extent to which animals, and particularly birds, use conspecifics as cues to establishing breeding and feeding territories. Conspecifics can be indicators of habitat quality, or they might intrinsically affect reproductive success. Here we discuss the implications of conspecific attraction for biologists who wish to conserve endangered species that are living in fragmented habitats.

CRITICAL THRESHOLDS ASSOCIATED WITH HABITAT LOSS FOR TWO VERNAL POOL-BREEDING AMPHIBIANS

A critical threshold exists when the relationship between the amount of suitable habitat and population density or probability of occurrence exhibits a sudden, disproportionate decline as habitat is lost. Critical thresholds are predicted by a variety of modeling approaches, but empirical support has been limited or lacking. We looked for critical thresholds in two pool-breeding amphibians that spend most of the year in adjacent upland forest: the spotted salamander (Ambystoma maculatum ) and the wood frog (Rana sylvatica). These species were selected because of their reported poor dispersal capacities and their dependency on forest habitat when not breeding. Using piecewise regression and binomial change-point tests, we looked for a relationship between the probability of oc- cupancy of a site and forest cover at five spatial scales, measuring forest cover in radial distances from the pond edge of suitable breeding ponds: 30 m, 100 m, 300 m, 500 m, and 1000 m. Using piecewise regression, we identified significant thresholds for spotted sala- manders at the 100-m and 300-m spatial scale, and for wood frogs at the 300-m scale. However, binomial change-point tests identified thresholds at all spatial scales for both species, with the location of the threshold (percent habitat cover required) increasing with spatial scale for spotted salamanders and decreasing with spatial scale for wood frogs. Thresholds for spotted salamanders occurred at ;30% forest cover at spatial scales of 100 m or less, with 41% cover at 500 m, and with 51% habitat cover at 1000 m. Thresholds for wood frogs ranged from 88% habitat cover at 30 m from the pond edge, declining to 44% habitat cover within 1000 m. These patterns might be explained by the different winter dispersions of these species. Knowing whether a species has a critical threshold, and at what level of cover and at what spatial scale it exists, would be essential for conservation of habitat-sensitive species.

Impacts of varying habitat quality on the physiological stress of spotted salamanders (Ambystoma maculatum)

We sampled blood from free-living spotted salamanders (Ambystoma maculatum) to test whether differences in the concentrations of a stress hormone (corticosterone) were associated with different qualities of breeding and migration habitat. Spotted salamanders are forest specialists that migrate to vernal pools to breed, and upland habitat degradation may have sub-lethal effects on animals that lead to population declines. An individual’s level of physiological stress may function as a biomonitor for sub-lethal effects, and thus as a biomonitor for ecosystem quality. We compared unstressed (baseline) and stress-induced corticosterone concentrations in spotted salamanders: (1) at sites that differed in amount of forest loss; (2) during breeding migration across forest habitat versus pavement; (3) in microhabitats that varied in soil drainage and canopy cover. Removal of large amounts of terrestrial habitat surrounding a breeding pond was correlated with lower baseline (in males) and stress-induced corticosterone concentrations, which may indicate healthy individuals with a reduced ability to respond to additional stress or individuals experiencing chronic stress. Male salamanders migrating across pavement had elevated baseline corticosterone concentrations compared to animals migrating through a forest, consistent with an acute stress response. However, concentrations of corticosterone did not differ between individuals in microhabitats with canopy cover and well-drained soil versus those in microhabitats with no canopy cover and/or swampy soil. This endocrinological technique may be one useful measure of a population’s health, helping to identify populations where further ecological study is recommended to evaluate conservation concerns.

Terrestrial habitat use and winter densities of the Wood Frog (Rana sylvatica)

Abstract Few studies have systematically investigated the overwintering ecology of anurans. We used large-scale field enclosures to measure the winter densities of Wood Frogs (Rana sylvatica) in an upland deciduous forest adjacent to two breeding pools in eastern Massachusetts. Pitfall traps associated with one of our enclosure arrays were operated continuously from March to December 2000. Wood Frog densities ranged from 0–6.3 Wood Frogs/100 m2 (x̄ = 1.4, SD = 1.6, N = 17 enclosures) and declined as distance to the nearest breeding pond increased. The sex ratio of Wood Frogs wintering close (< 65 m) to the pond was more highly skewed toward males than the sex ratio of Wood Frogs wintering further from the pond (8:1 vs. 1.6:1). Adult Wood Frogs apparently only occupied this upland forest habitat during late fall and winter and did not use it during the summer active period. These results suggest that few wintering females may be protected within narrow regulatory buffers adjacent to breeding ponds and that the effects of habitat destruction on Wood Frog mortality may vary dramatically by season.

Exogenous and endogenous corticosterone alter feather quality

We investigated how exogenous and endogenous glucocorticoids affect feather replacement in European starlings (Sturnus vulgaris) after approximately 56% of flight feathers were removed. We hypothesized that corticosterone would retard feather regrowth and decrease feather quality. After feather regrowth began, birds were treated with exogenous corticosterone or sham implants, or endogenous corticosterone by applying psychological or physical (food restriction) stressors. Exogenous corticosterone had no impact on feather length and vane area, but rectrices were lighter than controls. Exogenous corticosterone also decreased inter-barb distance for all feathers and increased barbule number for secondaries and rectrices. Although exogenous corticosterone had no affect on rachis tensile strength and stiffness, barbicel hooking strength was reduced. Finally, exogenous corticosterone did not alter the ability of Bacillus licheniformis to degrade feathers or affect the number of feathers that failed to regrow. In contrast, endogenous corticosterone via food restriction resulted in greater inter-barb distances in primaries and secondaries, and acute and chronic stress resulted in greater inter-barb distances in rectrices. Food-restricted birds had significantly fewer barbules in primaries than chronic stress birds and weaker feathers compared to controls. We conclude that, although exogenous and endogenous corticosterone had slightly different effects, some flight feathers grown in the presence of high circulating corticosterone are lighter, potentially weaker, and with altered feather micro-structure.

VARIATION IN TERRESTRIAL HABITAT USE BY FOUR POOL‐BREEDING AMPHIBIAN SPECIES

Abstract We conducted a 2-year study of terrestrial habitat use by spotted salamanders (Ambystoma maculatum), blue-spotted salamanders (A. laterale), wood frogs (Rana sylvatica), and eastern newts (Notophthalmus viridescens) within blocks of forest enclosed by drift fencing and pitfall traps in the vicinity of a single breeding pond. Adult winter densities within forest habitat <100 m from the breeding pond were low for all species (range 0.1–1.9 individuals / 100 m2, n = 6 enclosures). During our 2-year study, at least 40% of wood frogs, 52% of blue-spotted salamanders, and 60% of spotted salamanders wintered >100 m from the breeding pond. Males tended to winter closer to the breeding pond than did females. Adult wood frogs and eastern newts were largely absent from upland forest adjacent to the breeding pond during spring and summer, but they entered these areas in significant numbers to winter. Analyses of net flow of amphibians resulting from fall movement suggest that summer and winter densities of Ambystoma salamanders remained similar, while there were large increases in wood frog and eastern newt densities within terrestrial habitats near the breeding pond during fall. These results support a growing body of evidence that maintenance of suitable terrestrial habitat beyond 100 m from breeding pools is important for maintaining pool-breeding amphibian populations. Narrow protected buffer strips around breeding ponds might be even less effective than previously thought due to the disproportionate representation of males within these areas.

Evolution of a Major Drug Metabolizing Enzyme Defect in the Domestic Cat and Other Felidae: Phylogenetic Timing and the Role of Hypercarnivory

The domestic cat (Felis catus) shows remarkable sensitivity to the adverse effects of phenolic drugs, including acetaminophen and aspirin, as well as structurally-related toxicants found in the diet and environment. This idiosyncrasy results from pseudogenization of the gene encoding UDP-glucuronosyltransferase (UGT) 1A6, the major species-conserved phenol detoxification enzyme. Here, we established the phylogenetic timing of disruptive UGT1A6 mutations and explored the hypothesis that gene inactivation in cats was enabled by minimal exposure to plant-derived toxicants. Fixation of the UGT1A6 pseudogene was estimated to have occurred between 35 and 11 million years ago with all extant Felidae having dysfunctional UGT1A6. Out of 22 additional taxa sampled, representative of most Carnivora families, only brown hyena (Parahyaena brunnea) and northern elephant seal (Mirounga angustirostris) showed inactivating UGT1A6 mutations. A comprehensive literature review of the natural diet of the sampled taxa indicated that all species with defective UGT1A6 were hypercarnivores (>70% dietary animal matter). Furthermore those species with UGT1A6 defects showed evidence for reduced amino acid constraint (increased dN/dS ratios approaching the neutral selection value of 1.0) as compared with species with intact UGT1A6. In contrast, there was no evidence for reduced amino acid constraint for these same species within UGT1A1, the gene encoding the enzyme responsible for detoxification of endogenously generated bilirubin. Our results provide the first evidence suggesting that diet may have played a permissive role in the devolution of a mammalian drug metabolizing enzyme. Further work is needed to establish whether these preliminary findings can be generalized to all Carnivora.

REPORT OF THE AOU CONSERVATION COMMITTEE ON THE PARTNERS IN FLIGHT SPECIES PRIORITIZATION PLAN

STEVEN R. BEISSINGER,1,6 J. MICHAEL REED,2 JOSEPH M. WUNDERLE, JR.,3 SCOTT K. ROBINSON,4 AND DEBORAH M. FINCH5 1Department of Environmental Science, Policy and Management, 151 Hilgard Hall, University of California, Berkeley, California 94720, USA; 2Department of Biology, Tufts University, Medford, Massachusetts 02155, USA; 3International Institute of Tropical Forestry, USDA Forest Service, Box 490, Palmer, Puerto Rico 00721; 4Department of Ecology, Ethology and Evolution, University of Illinois, Champaign, Illinois 61820, USA; and 5Forestry Sciences Lab, USDA Forest Service, 2205 Columbia SE, Albuquerque, New Mexico 87106, USA

The corticosterone stress response and mercury contamination in free-living tree swallows, Tachycineta bicolor

We determined mercury concentrations in tree swallows, Tachycineta bicolor, from Massachusetts and Maine with different levels of contamination. Baseline and stress-induced plasma corticosterone concentrations from adults and nestlings (Massachusetts only) were compared with mercury concentrations. In Massachusetts, adult baseline corticosterone was negatively correlated with blood mercury, but showed a nearly-significant positive correlation with feather mercury. There was a negative relationship between baseline corticosterone and blood mercury in nestlings and between baseline corticosterone and egg mercury. There was no relationship between mercury and stress-induced corticosterone in any of the groups, or with baseline corticosterone in Maine sites where mercury levels were lower. The findings suggest blood and egg mercury may be a better indicator of current condition than feather mercury. Further, mercury contamination may not alter stress-induced corticosterone concentrations in tree swallows but appears to have a significant impact on baseline circulating corticosterone.

Life-history and viability analysis of the endangered Hawaiian stilt

The Hawaiian stilt Himantopus mexicanus knudseni is an endangered, endemic subspecies of black-necked stilt. We present life-history data required to perform population viability analysis (PVA), and the results of a series of PVAs under two scenarios, treating (a) the subspecies as a single population, and (b) six subpopulations as a metapopulation. We performed sensitivity analyses on model parameters and used results to address various management options. Both basic models predicted that stilts would increase to fill available habitat with no chance of a significant decline. Catastrophe, maximum age, and density-dependent reproduction had little effect on population projections. Rapid declines in the probability of stilt populations persisting occurred when clutch failure rate or first-year mortality rate increased above 70%, or when adult mortality rate increased above 30%. Model predictions of mean population size at 200 years tracked changes in carrying capacity. If current conditions change such that rates of clutch failure or stilt mortality increase, population declines and eventual extinction becomes more likely. Managers, therefore, should maintain predator control, limit water level fluctuations, and maintain current habitat area. Downlisting is not warranted because wetland management and predator control are necessary for Hawaiian stilts to persist.