Phillip D. Doerr

Delayed dispersal and reproduction as a life history tactic in cooperative breeders : fitness calculations from red-cockaded woodpeckers

The evolution of delayed dispersal and reproduction in cooperative breeders can be viewed as selection between alternative life-history tactics: (1) stay-and-foray (SAF), in which individuals delay dispersal and reproduction and compete for breeding vacancies in the vicinity of the natal territory, and (2) depart-and-search (DAS), in which individuals disperse soon after fledging to wander in search of a breeding vacancy. Using demographic data collected from red-cockaded woodpeckers (Picoides borealis), we evaluated a demographic model of the evolution of delayed dispersal and reproduction based on selection between these tactics. Because males of this species exhibit both tactics regularly, we could estimate all model parameters directly. Our estimates provide empirical support for key assumptions of demographic models of the evolution of delayed dispersal and reproduction, such as a disparity in survival between those adopting SAF and those adopting DAS during the first year of life, a low rate of successful dispersal in those practicing DAS, and low reproductive success at early ages among breeders. We show, in a population in which the fate of dispersers could be documented, that the fitness of individuals delaying dispersal and reproduction can equal or exceed that of individuals attempting early reproduction, even without indirect fitness benefits due to helping behavior.

RESPONSE OF GREAT HORNED OWL POPULATIONS TO CHANGING PREY DENSITIES1

From 1966 through 1969, we measured ie numbers, productivity, and food habits of great horned owls (Bubo virginianus) on an area of 62 square miles near Rochester, Alberta. During these years, there were sevenfold, twofold, and threefold increases in the numbers of snowshoe hares ( Lepus americanus), ruffed grouse (Bonasa umbellus), and sharp-tailed grouse (Pedioecetes phasianellus) re- spectively. The owls responded to these chzanges in numbers of prey by an increase in numbers from io to 18, by an increase from 20 to 100 percent in the proportion nesting, and by an increase in the percentage of snowshoe hare biomass in the diet from 23 percent in 1966 to 50 percent in 1969. The proportion of sharp-tailed grouse in the owl diet also increased from none in 1966 to 10 percent in 1968 but decreased to 3 percent in 1969. The proportion of ruffed grouse in the diet decreased each year, from 23 percent in 1966 to none in 1969. The diets of owl families were related to the vegetative cover surrounding the nests and presumably to the composittion o£ the prey base. Snowshoe hares, waterfowl, and pocket gophers (Thomomys talpoides) were the pnncipal components of the os^71 diet. The quantitative impact of owl predation on spring populations of snowshoe hares and ruffed grouse appeared to be low ( between 0 and 7 percent). Although 60 percent of the hares alive in spring were young-of-the-year, 97 percent of the hares in ie owl diet were adults. Similarly, only 3 of 26 grouse in the owl diet were females, despite balanced sex ratios in the spring grouse populations. The continued increase in numbers of snowshoe hares coincided with decreased predation rates on ruffed grouse and decreased incidence of sharp-tailed grouse in the owl diet, as owls consumed relatively more snowshoe hares. Abstract: From 1966 through 1969, we measured ie numbers, productivity, and food habits of great horned owls (Bubo virginianus) on an area of 62 square miles near Rochester, Alberta. During these years, there were sevenfold, twofold, and threefold increases in the numbers of snowshoe hares ( Lepus americanus), ruffed grouse (Bonasa umbellus), and sharp-tailed grouse (Pedioecetes phasianellus) re- spectively. The owls responded to these chzanges in numbers of prey by an increase in numbers from io to 18, by an increase from 20 to 100 percent in the proportion nesting, and by an increase in the percentage of snowshoe hare biomass in the diet from 23 percent in 1966 to 50 percent in 1969. The proportion of sharp-tailed grouse in the owl diet also increased from none in 1966 to 10 percent in 1968 but decreased to 3 percent in 1969. The proportion of ruffed grouse in the diet decreased each year, from 23 percent in 1966 to none in 1969. The diets of owl families were related to the vegetative cover surrounding the nests and presumably to the composittion o£ the prey base. Snowshoe hares, waterfowl, and pocket gophers (Thomomys talpoides) were the pnncipal components of the os^71 diet. The quantitative impact of owl predation on spring populations of snowshoe hares and ruffed grouse appeared to be low ( between 0 and 7 percent). Although 60 percent of the hares alive in spring were young-of-the-year, 97 percent of the hares in ie owl diet were adults. Similarly, only 3 of 26 grouse in the owl diet were females, despite balanced sex ratios in the spring grouse populations. The continued increase in numbers of snowshoe hares coincided with decreased predation rates on ruffed grouse and decreased incidence of sharp-tailed grouse in the owl diet, as owls consumed relatively more snowshoe hares.

Defining Quality of Red-Cockaded Woodpecker Foraging Habitat Based on Habitat Use and Fitness

Accurate understanding of habitat quality is a critical component of wildlife management. We developed a definition of high-quality foraging habitat for the red-cockaded woodpecker (Picoides borealis), a federally endangered, cooperatively breeding bird species, from analyses of resource selection and habitat use, relationships between fitness measures and habitat features, and an extensive literature review. In the North Carolina Sandhills, use of foraging habitat at the level of individual trees, habitat patches, and forest stands was strongly and positively related to age and size of pines (Pinus spp.). Use of habitat patches and forest stands was greatest at intermediate densities of medium-sized and large pines and was negatively associated with hardwood and pine midstory. Size of red-cockaded woodpecker groups, an important fitness measure for this species, was positively related to density of old-growth pines within the home range and negatively related to density of medium-sized pines and height of hardwood midstory. Similar results were reported by 2 other studies. High-quality foraging habitat for red-cockaded woodpeckers, therefore, contains sparse or no midstory, intermediate densities of medium-sized and large pines, and old-growth pines in at least low densities. Although we documented a relationship between group size and the amount of habitat meeting our definition of high quality, we were unable to identify the optimum amount of high-quality habitat to provide per group because most study groups had relatively little high-quality foraging habitat. Both fitness and habitat selection in our study population may be constrained by quality and quantity of foraging habitat. James et al. (2001) recommended, and we strongly agree, that foraging habitat be managed for abundant herbaceous ground cover, low densities of small and medium-sized pines, and moderate densities of large pines. We also stress the importance of old-growth pines in foraging habitat. Because the structure of high-quality foraging habitat is similar to that of high-quality nesting habitat, we recommend that management of these 2 be increasingly integrated.

Characteristics of winter feeding aggregations of ruffed grouse in Alberta

Winter feeding aggregations of ruffed grouse (Bonasa umbellus) were studied near Roch- ester, Alberta. The annual onset of budding by grouse in fall commenced with the first snow cover. During two winters, aggregation size increased through mid-January, after which there was a significant linear decrease averaging nearly 50 percent by early April. The decrease in group size after mid-January was probably effected chiefly by fragmentation resulting from increasing intragroup strife. Sex and age structure of aggregations was not significantly different from that expected by random combinations. Ruffed grouse fed in male aspen (Populus tremuloides) or in willow (Salix spp.) for an average of 16 minutes during morning, usually leaving at sunrise. Feeding began in evening about 52 minutes after sunset, and lasted an average of 24 minutes. The mean age of 100 male aspen utilized by grouse near Rochester was 36 years. Tree densities at 12 feeding sites were significantly higher than those at systematic-grid stations, drumming logs, and kill sites within aspen stands at Rochester. Buds and twigs of aspen and willow comprised about 80 percent (by volume) of crop contents of 148 grouse shot while budding. Nutrient analyses of male aspen buds indicated that ruffed grouse ingested those buds having the highest protein and potassium contents. Willow buds from grouse crops contained more protein (14.0 percent) than aspen buds from two other groups of crops (12.9 and 11.7 percent).

Broad-Winged Hawk Nesting and Food Habits

COMPARED to the literature on other species of raptors, relatively little has been published on the Broad-winged Hawk (Buteo platypterus). Although clutch size (Burns, 1911) and food habits (May, 1935, and others) are well-documented in this species, little information is available on fledging rates and nesting densities. Similarly, reports on Broadwing ecology in the northern part of their breeding range are scarce. This paper describes the nesting density, productivity, and food habits of a breeding population of Broad-winged Hawks near Rochester, Alberta. Central Alberta, the locale of this study, is on the northwestern fringe of the Broad-winged Hawk range in North America (Burns, 1911; May, 1935; Bent, 1937). Reptiles and amphibians, which are important components of this hawks diet in more southern latitudes, are scarce in central Alberta. We were especially interested in the incidence of these prey items in the Broad-wing diet in our area, and in evaluating the possibility that their scarcity limits the northern distribution of this raptor.

Using Video Surveillance to Estimate Wildlife Use of a Highway Underpass

Abstract Roads pose many threats to wildlife including wildlife–vehicle collisions, which are a danger to humans as well as wildlife. Bridges built with provisions for wildlife can function as important corridors for wildlife passage. We used video surveillance to record wildlife passage under a bridge near Durham, North Carolina, USA, to determine whether it functioned as a wildlife underpass. This is particularly important for white-tailed deer (Odocoileus virginianus) because forests associated with the bridge created a corridor between 2 natural areas. We calculated detection probabilities and estimated the number of crossings as observed crossings divided by detection probability. We observed 126 crossings by >10 species of mammals. Detection probability was 42%; therefore, an estimated 299 wildlife crossings occurred. We observed 75 deer: 17 deer approached the underpass and retreated. We estimated sighting 40% of deer crossings and 92% of deer approaches. Thus, an estimated 185 deer crossings and 18 approaches occurred. As an index of road mortality, we conducted weekly surveys of vehicle-killed animals on a 1.8-km section containing the underpass. We discovered only 5 incidences of animals killed by vehicles. The size and design of the bridge promoted wildlife use of the underpass, providing landscape connectivity between habitats on opposite sides of the highway and likely increasing motorist safety. Thus, bridges in the appropriate landscape context and with a design conducive to wildlife use, can function as a corridor to reduce the effects of fragmentation.

Eastern wild Turkey reproduction in an area subjected to flooding

We used cohort analyses and population cohort matrices to model a wild turkey (Meleagris gallopavo silvestris) population under perturbed (i.e., man-induced flooding on 3-yr intervals) and unperturbed (i.e., non-flood) conditions. The net reproductive rate (R o ) of a cohort in which reproduction in the hatching-year (HY) age class was perturbed by flooding dropped to 0.460 from R o = 1.383 for unperturbed cohorts. The R o of cohorts in which only after-hatching-year (AHY) age classes were exposed to flooding was >1.0. Cohort analyses demonstrated the importance to the population of nesting by HY hens and the significant effects on cohort reproductive potential of exposing the HY age class to flooding. Evaluation of population cohort matrices also suggested that flooding on a 3-year interval precludes sufficient reproduction to maintain this wild turkey population.

Inbreeding rate and effective population size: A comparison of estimates from pedigree analysis and a demographic model

Abstract Demographic models have been used to calculate effective population size, (Ne) which is a measure of the expected rate of loss of genetic variability. However, accurately calculating effective size for most populations of wild vertebrates is difficult because the required demographic or pedigree data are unavailable. We used data from a long-term study of the endangered red-cockaded woodpecker Picoides borealis in south-central North Carolina to construct a pedigree, which we then used to calculate the realized rate of inbreeding (F). We compared our values, estimated via pedigree analysis, with published, expected values of F calculated from a demographic model. The change in inbreeding coefficient per generation (ΔF) based on a demographic model fell below the 95% confidence limit around the pedigree value. Thus, ΔF, as calculated from a demographic model, significantly underestimated the ΔF estimated via pedigree analysis. We suggest that a multi-method approach can be useful to managers in increasing the accuracy of estimates of rate of loss of genetic variability.

Isolation of Mycoplasma gallopavonis from Free-ranging Wild Turkeys in Coastal North Carolina Seropositive and Culture-negative for Mycoplasma gallisepticum

Serum samples and choanal cleft swabs were collected from livetrapped and hunter killed wild turkeys (Meleagris gallopavo) from Martin and Bertie counties, North Carolina (USA). Sera were tested for antibodies to Mycoplasma gallisepticum, Mycoplasma synoviae and Mycoplasma meleagridis by hemagglutination inhibition (HI). Sera from 33% (five of 15) of livetrapped turkeys were positive for antibodies to M. gallisepticum by HI, and all were negative for antibodies to M. synoviae and M. meleagridis. Choanal cleft swabs from 22 livetrapped and five hunter killed wild turkeys cultured in Freys broth medium resulted in 23 mycoplasma isolations. Using direct immunofluorescence, 74% (17/23) were M. gallopavonis, and 26% (six of 23) were unidentified; no isolate was identified as M. gallisepticum, M. synoviae or M. meleagridis.