Daniel B. Stotts

Bio: Daniel B. Stotts is an academic researcher. The author has contributed to research in topics: Population & Anas. The author has an hindex of 5, co-authored 6 publications receiving 226 citations.

Winter survival of female American black ducks on the Atlantic coast

Abstract: We used radio telemetry to monitor the winter survival and cause-specific mortality of 227 female American black ducks (Anas rubripes) captured in New Jersey and Virginia, 1983-85. Mean survival rate for 19 December-15 February was 0.65. Survival from hunting and nonhunting risk was 0.84 and 0.78, respectively. Causes of nonhunting mortality included predation and emaciation (winter stress). After-hatchyear (AHY) ducks had a higher probability of survival than hatch-year (HY) ducks (0.73 vs. 0.60); most of this difference was related to survival from nonhunting risk. After-hatch-year ducks with body masses > median had a higher survival probability (0.85) than AHY ducks with < median body masses (0.61) because of differential survival from hunting risk. Hatch-year ducks had lower body mass than AHY ducks, but among HY ducks body mass was not related to survival. There were no consistent patterns in survivorship in relation to mean daily temperature, although the timing of the onset of low temperatures and storms may have influenced movement patterns. Our estimated survival rates are consistent with estimates from other studies of seasonal and annual survival. It may be possible to manage habitats for population segments at high risk (HY and low body mass birds), and increase black duck survivorship. J. WILDL. MANAGE. 53(1):99-109 Populations of American black ducks have declined from the 1950's to present (Barske 1968, Grandy 1983, Feierabend 1984). Reasons for the decline are unknown but may be related to specific causes of mortality such as hunting (Blandin 1982, Krementz et al. 1988), predation (Ringelman and Longcore 1983), competition from and hybridization with mallards (Anas platyrhynchos) (Johnsgard 1961, 1967), and habitat losses (Barske 1968). Winter is a critical time for black ducks, because of high energetic demands (Albright 1981, Reinecke et al. 1982). Reinecke et al. (1982) demonstrated that immature females achieved adult structural size, but were lighter in weight and had smaller nutrient reserves than did adults during their first winter. Other studies have corroborated a link between age, body condition, and probability of survival. Hepp et al. (1986) reported that the probability of being shot by hunters for mallards in poor condition was higher than for those in better condition. Haramis et al. (1986) reported a direct relationship between the body mass of canvasbacks (Aythya valisineria) in early winter and probability of surviving the winter. Although immature black ducks are more vulnerable to hunting (Schierbaum and Foley 1957, Krementz et al. 1988), and have lower annual survival rates than do adults (Blandin 1982, Krementz et al. 1987), whether age-specific mortality persists through winter, or occurs primarily during the postfledging period and early hunting season is unknown. Managers need estimates of winter survival rates and identification of mortality sources to understand black duck population dynamics and assist in the management of black duck populations. Our objectives were to estimate survival rates of black ducks during winter, examine specific components of mortality, specifically hunting versus nonhunting mortality, and examine variation in survival rates during winter in relation to age, body condition, time, geographic location, and weather conditions. We appreciate the assistance of E. L. Derleth, N. Dietz, B. Dirks, B. L. Estel, S. Holzman, A. G. Larochelle, J. M. Morton, H. H. Obrecht III, S. R. Perin, N. Phelps, H. G. Russell, M. A. Spoden, J. M. Walsh, and G. Wright in the collection of field data. We also thank F. Ferrigno, New Jersey Fish and Game, G. L. Inman and D. L. Beall of Forsythe National Wildlife Refuge, and D. Holland of Chincoteague National 'Present address: Georgia Cooperative Fish and Wildlife Research Unit, School of Forest Resources, University of Georgia, Athens, GA 30602.

Evaluation of Aerial Transect Surveys for Wintering American Black Ducks

Abstract: We used an experimental aerial transect survey with stratified random sampling, to estimate the size of the population of wintering black ducks (Anas rubripes) in coastal New Jersey during 2 winters, and the coastal Atlantic Flyway (Me. to S.C.) during 4 years. Population estimates were precise (CV 2 x MWS. Because of the lack of statistical design, precision cannot be estimated. Also, because an attempt is made to survey all waterfowl habitats and species, the results are likely not precise for any 1 species. Our objectives were to design a survey to provide precise estimates of the size of the Atlantic Flyway black duck population during winter, compare our results with those of the MWS during the same periods in terms of ac' Present address: Georgia Cooperative Fish and Wildlife Research Unit, School of Forest Resources, University of Georgia, Athens, GA 30602.

Survival of American Black Ducks radiomarked in Quebec, Nova Scotia and Vermont

Abstract: We monitored survival of 397 radiomarked juvenile American black ducks (Anas rubripes) distributed among Les Escoumins (n = 75) and Kamouraska, Quebec (n = 84). Amherst Point, Nova Scotia (n = 89), and a site on the Vermont-Queber border (n = 149) during autumn 1990 and 1991. Eighty-six percent (215 of 250) of all confirmed mortalities during the study was from hunting: 72% of marked ducks were shot and retrieved and 14% were shot and unretrieved. We tested for differences in survival in relation to sex, body mass, year (1990-91, 1991-92), and among the 4 locations for each of 2 monitoring periods (early, EMP: late. LMP). With data from the EMP for Vermont-Quebec in 1990 and 1991, Les Escoumins in 1990, and Amherst Point in 1991, survival of hatching-year (HY) males and females did not differ (P = 0.357). For sexes combined for the EMP, survival of ducks was greater in 1991 than 1990 (P = 0.086), and differed among locations (P = 0.013). Survival (years combined was greater al Amherst Point than at Kamouraska (P = 0.003) and Vermont Quebec (P = 0.002) during the EMP. The highest survival rate at Amherst Point (0.545 ± 0.056 [SE]) was associated with the latest date (S Oct) of season opening: the lowest survival rate (0.395 ± 0.043) was at the Vermont-Quebec border, where hunter numbers and activity were greatest. For the LMP. no interaction between years and locations was detected (P = 0.942), and no differences in survival existed between vears (P = 0.102) and among locations (P = 0.349). No association was detected between body mass at capture and survival of combined males and females during the EMP (P = 0.572) or during the LMP (P = 0.965). When we censored hunting losses for combined years for each period. EMP or LMP, all survival estimates exceeded 0.800 (0.809-0.965). These data emphasize need for an improved harvest strategy for American black ducks in North America to allow for increases in breeding populations to achieve population goals.

Comparative productivity of American black ducks and mallards nesting on Chesapeake Bay islands

Abstract: We estimated laying dates, clutch sizes, and nest success rates of sympatrically breeding populations of American black ducks (Anas rubripes) and mallards (Anas platyrhynchos) on Chesapeake Bay islands between 1986 and 1989. Neither average laying date nor clutch size differed between black ducks and mallards. Nest success rates were higher for mallards in 2 of 4 years, but were area dependent.

Historical changes in laying date, clutch size, and nest success of American black ducks

Abstract: The breeding population of American black ducks (Anas rubripes) on Chesapeake Bay has declined over the past 30 years. We tested whether there have been changes in laying date, clutch size, and nest success of breeding black ducks on islands in Chesapeake Bay between the 1950's and 1980's. None of these variables differed significantly between decades, suggesting that other factors must be responsible for the decline in locally breeding black ducks. J. WILDL. MANAGE. 55(3):462-466 Many factors might contribute to declines in populations of American black ducks, including habitat alteration and loss (Dennis et al. 1985, Diefenbach and Owen 1989), overharvest (Geis et al. 1971, Grandy 1983), pollution (Longcore and Stendell 1982, Haramis and Chu 1987), and competition and/or hybridization with mallards (A. platyrhynchos) (Johnsgard and DiSilvestro 1976). Any of these could conceivably affect the breeding success of black ducks. Populations of black ducks have declined on Chesapeake Bay since the 1950's (Breeding Bird Surv., Off. Migr. Bird Manage., U.S. Fish Wildl. Serv., unpubl. data). We tested whether laying dates, clutch sizes, and nest success rates of black ducks differed between the 1950's and 1980's by comparing recent data with data collected by Stotts and Davis (1960) in the same area. Laying date was examined not only because it partially explains seasonal changes in clutch size (Klomp 1970), but also because it partially explains the seasonal decline in duckling survival rates (Orthmeyer and Ball 1990). We thank landowners granting us access to their lands. We also thank C. L. Holmquist and J. W. Gill for assistance in the field, G. W. Pendleton for assistance with the statistical analyses, and J. R. Serie, G. R. Hepp, I. J. Ball, and D. J. Forsell for valuable comments on early drafts. Funding was partially provided under PittmanRobertson Project Number W-30-R.

Program MARK: survival estimation from populations of marked animals

Abstract: MARK provides parameter estimates from marked animals when they are re-encountered at a later time as dead recoveries, or live recaptures or re-sightings. The time intervals between re-encounters do not have to be equal. More than one attribute group of animals can be modelled. The basic input to MARK is the encounter history for each animal. MARK can also estimate the size of closed populations. Parameters can be constrained to be the same across re-encounter occasions, or by age, or group, using the parameter index matrix. A set of common models for initial screening of data are provided. Time effects, group effects, time x group effects and a null model of none of the above, are provided for each parameter. Besides the logit function to link the design matrix to the parameters of the model, other link functions include the log—log, complimentary log—log, sine, log, and identity. The estimates of model parameters are computed via numerical maximum likelihood techniques. The number of parameters that are...

Depletion, Degradation, and Recovery Potential of Estuaries and Coastal Seas

Abstract: Estuarine and coastal transformation is as old as civilization yet has dramatically accelerated over the past 150 to 300 years. Reconstructed time lines, causes, and consequences of change in 12 once diverse and productive estuaries and coastal seas worldwide show similar patterns: Human impacts have depleted >90% of formerly important species, destroyed >65% of seagrass and wetland habitat, degraded water quality, and accelerated species invasions. Twentieth-century conservation efforts achieved partial recovery of upper trophic levels but have so far failed to restore former ecosystem structure and function. Our results provide detailed historical baselines and quantitative targets for ecosystem-based management and marine conservation.

The ecological costs of avian fat storage

Abstract: Avian fat storage is associated with both benefits and costs. Although the benefits of maintaining higher energetic reserves have long been considered, the associated costs have received far less attention. Spatial and temporal patterns of fat storage, together with experimental data, indicate that birds are capable of actively regulating their energetic reserves at levels below physiological or environmental maxima. This regulation implies that fat storage entails a cost. Evidence of potential costs are reviewed and discussed under the following headings: mass-dependent metabolism, mass-dependent predation risk, mass-dependent risk of injury, mass-dependent foraging, pathological costs and reproductive costs. Although the evidence that fat storage is costly is convincing, key empirical data are lacking. We indicate the sorts of data which need to be gathered and suggest ways in which this might be done. We go on to discuss the interaction of these costs and their relevance to between-individual patterns of fat storage and the interpretation of ‘condition indices’. Because many of the purported costs of fat storage are dependent upon changes in body mass, or wing loading, our review is also relevant to other phenomena which may involve mass-dependent costs, such as gonadal hypertrophy, transport of food items and primary moult.

Non-indigenous species as stressors in estuarine and marine communities: Assessing invasion impacts and interactions

Abstract: Invasions by non-indigenous species (NIS) are recognized as important stressors of many communities throughout the world. Here, we evaluated available data on the role of NIS in marine and estuarine communities and their interactions with other anthropogenic stressors, using an intensive analysis of the Chesapeake Bay region as a case study. First, we reviewed the reported ecological impacts of 196 species that occur in tidal waters of the bay, including species that are known invaders as well as some that are cryptogenic (i.e., of uncertain origin). Second, we compared the impacts reported in and out of the bay region for the same 54 species of plants and fish from this group that regularly occur in the region’s tidal waters. Third, we assessed the evidence for interaction in the distribution or performance of these 54 plant and fish species within the bay and other stressors. Of the 196 known and possible NIS, 39 (20%) were thought to have some significant impact on a resident population, community, habitat, or process within the bay region. However, quantitative data on impacts were found for only 12 of the 39, representing 31% of this group and 6% of all 196 species surveyed. The patterns of reported impacts in the bay for plants and fish were nearly identical: 29% were reported to have significant impacts, but quantitative impact data existed for only 7% (4/54) of these species. In contrast, 74% of the same species were reported to have significant impacts outside of the bay, and some quantitative impact data were found for 44% (24/54) of them. Although it appears that 20% of the plant and fish species in our analysis may have significant impacts in the bay region based upon impacts measured elsewhere, we suggest that studies outside the region cannot reliably predict such impacts. We surmise that quantitative impact measures for individual bays or estuaries generally exist for ,5% of the NIS present, and many of these measures are not particularly informative. Despite the increasing knowledge of marine invasions at many sites, it is evident that we understand little about the full extent and variety of the impacts they create—singly and cumulatively. Given the multiple anthropogenic stressors that overlap with NIS in estuaries, we predict NIS‐stressor interactions play an important role in the pattern and impact of invasions.