Thomas A. Gavin

Reproductive Correlates of Breeding‐Site Fidelity in Bobolinks (Dolichonyx Oryzivorus)

To investigate the relationship between reproductive success (RS) and breeding—site fidelity in a transequatorial migrant, we studied two populations of marked Bobolinks (Dolichonyx oryzivorus) in upstate New York during 1982—1985. At these sites, 44% of the males and 25% of the females resident in one year returned in one or more subsequent years. There were more nests built, eggs laid, eggs hatched, and young fledged in territories of returning males in this polygynous species than in territories of males that did not return in subsequent years (P < .04). For females that returned, the number of eggs hatched, young fledged, young fledged on last nest attempt, and young fledged per egg laid were higher than for females that did not return (P < .02). Discriminant function analysis and data from 1982—1984 were used to predict correctly the return behavior of 30 to 42 individuals (sexes combined) in 1985, based on their reproductive success (RS) in 1984 (P < .01). Using data on RS and return rate for all years, the best single—variable model for males based on the number of young fledged from each territory classified correctly 59 of 85 individuals (69%) as returning or not (P < .005). The best single—variable model for females based on the number of yound fledged on their last nest attempt classified correctly 61 of 86 individuals (71%; P < .005). Using all data for 1982—1985, sex—specific models that included only whether an individual fledged one or more young classified correctly the same proportion as the best single—variable models above. However, among males that fledged one or more young, those that returned had fledged significantly more young the previous year than those that did not return (P < 0.5). Not all individuals that failed to return were dead, because five individuals that did not return to our study sites were captured in a subsequent year at another site. We concluded that male and female Bobolinks used information on their breeding success in one year to influence their choice of breeding site in the next year.

Microgeographic distribution of immature Ixodes dammini ticks correlated with that of deer

ABSTRACT. In order to determine whether the small‐scale distribution of immature Ixodes dammini Spielman et al. corresponds closely to the activity patterns of white‐tailed deer, Odocoileus virginianus (Zimmerman), these relationships were examined in a site on Long Island, New York, U.S.A. We first determined the extent and temporal pattern of adult ticks feeding on deer by examining twenty‐three resident deer tranquilized during September‐December 1985.1, dammini adults infested deer throughout this fall period, most abundantly during October and November. With radio‐telemetry collars attached to deer we determined the relative frequency that they occupied 0.25 ha quadrats of the study site. During the following summer, we examined white‐footed mice, Peromyscus leucopus (Rafmesque), that inhabited these quadrats and removed immature ticks from each. 8975 larval and 163 nymphal /. dammini were removed from 208 mice trapped in forty‐three such quadrats. The frequency of deer using these quadrats was positively correlated with both the number of larval and of nymphal ticks per mouse. These results suggest that risk of I.dammini‐borne zoonotic disease may be decreased by locally reducing deer density in sites that experience intense human activity.

Patterns of extra-pair fertilizations in bobolinks

SummaryWe studied patterns of paternity in 840 nestling bobolinks (Dolichonyx oryzivorus) from 191 pairbonded adults and the chicks they reared in west central New York, USA, during 1983–1986, using allozyme data (4 variable loci). Thirty-six (4.3%) nestlings exhibited genotypes that excluded a putative parent as a genetic parent. Using the method of Westneat et al. (1987) we estimated that 14.6% of the nestlings were sired by extrapair copulations and that 28% of the nests contained ≥ 1 nestling resulting from extra-pair fertilizations (EPFs). Rates of EPFs did not appear to be related to population density among our bobolink populations. Younger males and older females were more likely to have young in their nests sired by EPFs than were older males and younger females. Primary females (i.e., firstmated) of socially polygynous males were more likely to have young sired by EPFs than were secondary females; socially monogamous females had intermediate rates of mismatched offspring. Nestlings resulting from EPFs were not more frequent in nests of socially polygynous males than in nests of socially monogamous males. Males responsible for EPFs were probably nearby (within 2 territories) residents.

BREEDING BIRD DENSITY IN WOODLOTS: EFFECTS OF DEPTH AND BUILDINGS AT THE EDGES

A model is presented that describes the breeding bird density of a species in a woodlot, given that this density may change from edge to interior. The primary variable is a measure of depth in the woodlot that depends on distances to four woodlot edges. The model applies to forest-interior species and to edge species, and it also accounts for different degrees of threat or attraction at different edges. During 1993-1996, we collected bird abundance data using point counts at 387 sample plots in 176 woodlots, including two big woods (>5000 ha), in eastern Pennsylvania, USA. Models were developed for 36 species by using nonlinear regression guided by tests of residuals against other variables measured at each sample plot. Densities of 20 of the 36 species were affected by the depth in the woodlot. The density of one forest-interior species, Ovenbird (Seiurus aurocapillus), de- creased farther away from the big woods, which can be explained qualitatively by dispersal dynamics. Densities of 21 of the 36 species were affected by buildings near the woodlots: 10 species increased, and 11 decreased. One preliminary conservation conclusion is that it is important to preserve big woods (>5000 ha) because at least one common forest species (Ovenbird) might disappear from nearby woodlots if the big woods were to become fragmented. A second conservation conclusion is that certain species can persist only in the absence of nearby buildings. Perhaps these species would persist near buildings if the negative biotic interactions associated with buildings were removed, but more information is needed before this possibility can be evaluated. Our model-building procedure and sta- tistical approach might be useful for modeling a number of variables concerning birds or other animals in various habitats where edge effects are important.

Characterization of microsatellite loci in the Northern Idaho ground squirrel Spermophilus brunneus brunneus

rarest sciurid in North America. A northern (S. b. brunneus) and a southern subspecies (S. b. endemicus) have recently been described (Yensen 1991). The former is currently found in only 18 populations in Adams and Valley counties (west–central Idaho); the largest population is < 300 animals and the subspecies consists of < 1000 animals (Yensen & Sherman, in press). Reductions in S. b. brunneus’s range and population sizes are apparently due to major alterations of the habitat in the last 100 years. Many of the resultant small disjunct populations have recently become extinct, and others are in imminent danger of extinction. Previously we used allozymes to study mating behaviour (Sherman 1989) and population structure (T. A. Gavin et al. unpublished data). Recently we developed microsatellite markers in S. b. brunneus to enhance the resolving power of our data for understanding the extant and historical population structuring of S. b. brunneus, prior to restorative efforts. Samples of S. b. brunneus consisted of (i) blood taken from the suborbital sinus or (ii) buccal scrapings taken with a toothpick and placed in 1.5-mL cryovials and either air-dried or immersed in 0.5 mL of lysis buffer (White & Densmore 1992). DNA was extracted from 150 to 200 μL blood or buccal scrapings using QIAGEN Blood Kits. Genomic libraries were constructed from the DNA from a single individual by digesting with Sau3AI, ligating into pUC 18, and transforming DH5α competent cells (see May et al. in press for more detail). One library of 196 colonies (Library I) was dot-blotted and screened with total genomic DNA. A second library of 53 000 colonies (Library II) was lifted and screened with trimer and tetramer oligonucleotides from BIOS Laboratories (AAAT, AAAG, AAAC, CCG, AAG, AAT, AAC, and CAG). Total genomic DNA and oligos were end labeled (tailed) with either the Oligonucleotide 3′-End Labeling Kit or the Oligonucleotide Tailing Kit from Boehringer Mannheim. Positives were detected with the Lumi-Phos Chemiluminescent Kit or the colorimetric (chromogenic) method using the NBT/BCIP Kit (Boehinger Mannheim). Initially positive colonies were screened two more times for confirmation. Tertiary positives with inserts of 300–1500 bp were sequenced on an ABI 373A automated sequencer. Microsatellite sequences were located in 8/8 positives from Library I and 17/26 positives from Library II, and primers were designed for five and 15 of the sequences, respectively. Polymerase chain reaction amplifications were carried out in an MJR PTC-100 thermocyler in 50-μL reactions containing 3–10 ng DNA, 1.5 mM MgCl2, 0.4 μM each primer, 175 μM dNTPs, and 1 unit of GIBCO Taq. Amplification conditions were 94 °C for 3 min; 34 cycles of 94 °C for 1 min, 52° (57 °C for IGS-BM1) for 30 s, and 72 °C for 30 s; and a final extension of 5 min at 52 °C (or 57 °C). Amplified samples were concentrated from 25 μL down to 10 μL in a vacuum centrifuge and run on 4% 1 × TBE MetaPhor (FMC) agarose gels (Fig. 1) at 460 V (17 V/cm), with the circulating buffer (0.5 × TBE) at 12 °C for the first 5 min and the remainder of the run at 20 °C. Gels were run for 45 min to 1.5 h depending on size of PCR product (about 15 min per 25 base pairs). Gels were stained with ethidium bromide. The amplification effectiveness of the 20 primer pairs was tested against the clone and three individual squirrel DNA extracts. Thirteen pairs produced a resolvable amplicon in all four samples. The other seven amplified only in the clone or did not produce sufficient product to be useful. Each of the useable 13 primer pairs was subsequently tested against 10 individuals from across the range of S. b. brunneus. Primer sequences, GenBank accession numbers, repeat motif, clone amplicon size, and number of alleles detected for these 13 loci are presented in Table 1. The first three loci were from Library I and the latter 10 loci were from Library II. Usually only the primary amplicons were observed, as well as one or two heteroduplex bands in heterozygous individuals, demonstrating that amplification was PRIMER NOTE

HABITAT FRAGMENTATION LOWERS SURVIVAL OF A TROPICAL FOREST BIRD

Population ecology research has long been focused on linking environmental features with the viability of populations. The majority of this work has largely been carried out in temperate systems and, until recently, has examined the effects of habitat fragmentation on survival. In contrast, we looked at the effect of forest fragmentation on apparent survival of individuals of the White-ruffed Manakin (Corapipo altera) in southern Costa Rica. Survival and recapture rates were estimated using mark-recapture analyses, based on capture histories from 1993 to 2006. We sampled four forest patches ranging in size from 0.9 to 25 ha, and four sites in the larger 227-ha Las Cruces Biological Station Forest Reserve (LCBSFR). We found a significant difference in annual adult apparent survival rates for individuals marked and recaptured in forest fragments vs. individuals marked and recaptured in the larger LCBSFR. Contrary to our expectation, survival and recapture probabilities did not differ between male and female manakins. Also, there was no support for the existence of annual variation in survival within each study site. Our results suggest that forest fragmentation is likely having an effect on population dynamics for the White-ruffed Manakin in this landscape. Therefore, populations that appear to be persisting in fragmented landscapes might still be at risk of local extinction, and conservation action for tropical birds should be aimed at identifying and reducing sources of adult mortality. Future studies in fragmentation effects on reproductive success and survival, across broad geographical scales, will be needed before it is possible to achieve a clear understanding of the effects of habitat fragmentation on populations for both tropical and temperate regions.

Why Ask "Why": The Importance of Evolutionary Biology in Wildlife Science

The kinds of questions we ask in wildlife biology are at least as important as the methods we use to get answers to questions in research. In this essay, I urge wildlife biologists to vigorously pursue why questions rather than how questions or descriptive studies that should serve only as a starting point for our investigations. Behavioral ecologists are currently involved in a debate over explanations for biological phenomena called levels of analysis : how many are there, what terms and definitions apply to each level, and the importance of clearly identifying which level an explanation emanates from given that there are correct explanations for the same phenomenon at each level

AVIAN COMMUNITY DYNAMICS IN A FRAGMENTED TROPICAL LANDSCAPE

As humans alter habitats worldwide, developing reliable methods of assessing biodiversity and community attributes of interest (e.g., species richness, turnover, and extinction rates) is important. Frequently, estimates of community-level attributes are biased because the estimators make assumptions of the data that are violated; many published studies assume equal detectability across species, sites, or time. The accuracy of estimators of species richness and community-level vital rates (e.g., extinction and colonization) can be increased by using probabilistic estimation methods, which do not assume that all species are detected, or that the data assume a particular statistical distribution. Using these estimation methods, we examined avian community dynamics in a fragmented tropical landscape using data from five years of a mark–release–recapture study. For the resident understory avifauna in each of five small (∼0.3–20 ha), isolated forest fragments in southern Costa Rica, we estimated species richnes...

Population Genetic Structure of the Northern Idaho Ground Squirrel (Spermophilus brunneus brunneus)

Spermophilus brunneus is one of the rarest species of North American ground squirrels. It occurs in just five counties in western Idaho. We sampled blood from 14–64 individuals in 11 populations of the northern subspecies S. b. brunneus . Analyses of allozymes at five polymorphic loci revealed significant population structure ( F st = 0.167). Four populations located within a 2-km radius in Bear Meadow (Adams Co.) were indistinguishable with respect to allelic frequencies (Neis D = 0.002), but the remaining seven, more distant populations (also in Adams Co.) were differentiated from this group and from each other. F ST values ranged from 0.034 to 0.124 when the four populations in Bear Meadow were pooled and compared with each of the seven isolated populations. Regression of Slatkins M against geographic distance among the 55 pairwise comparisons of populations suggested a strong effect of isolation-by-distance, consistent with a one-dimensional stepping-stone model of gene flow. Significant genetic structure in S. b. brunneus populations apparently is due to genetic drift in populations with small Ne (i.e., 20–50), reinforced by lack of gene flow following recent habitat fragmentation. Fragmentation results from the shrinking of meadows due to invasion by conifers, itself the consequence of fire suppression in the past 100 years.

THE IMPORTANCE OF SOIL MOISTURE AND LEAF COVER IN A FEMALE LIZARD'S (NOROPS POLYLEPIS) EVALUATION OF POTENTIAL OVIPOSITION SITES

The microenvironment surrounding a lizard egg will strongly influence its probability of hatching, yet little is known about which environmental cues females use to select favorable nest sites. We conducted three experiments using Norops polylepis (Polychrotidae) in semi-natural enclosures to determine a females ability to assess soil moisture levels and the presence of leaf-litter cover when selecting an oviposition site. Females laid significantly more eggs in moist soil (42% water content) than in the dry (10%) and saturated (70%) soil treatments. Most eggs (72%) placed in moist soil treatments hatched, whereas none of the eggs in the dry and saturated soil treatments hatched. In a separate choice experiment, females laid significantly more eggs in a “soil-and-leaf-cover” treatment than in “soil-only” or “leaf-cover-only” treatments. Our results demonstrate that female N. polyelpis can detect variations in water content and leaf cover, and that females prefer microhabitats that likely maximize the survival of their eggs.