Stephen J. Dinsmore

ADVANCED TECHNIQUES FOR MODELING AVIAN NEST SURVIVAL

Estimation of avian nest survival has traditionally involved simple measures of apparent nest survival or Mayfield constant-nest-survival models. However, these methods do not allow researchers to build models that rigorously assess the importance of a wide range of biological factors that affect nest survival. Models that incorporate greater detail, such as temporal variation in nest survival and covariates representative of individual nests represent a substantial improvement over traditional estimation methods. In an attempt to improve nest survival estimation procedures, we introduce the nest survival model now available in the program MARK and demonstrate its use on a nesting study of Mountain Plovers (Charadrius montanus Townsend) in Montana, USA. We modeled the daily survival of Mountain Plover nests as a function of the sex of the incubating adult, nest age, year, linear and quadratic time trends, and two weather covariates (maximum daily temperature and daily precipitation) during a six-year stud...

ANNUAL SURVIVAL AND POPULATION ESTIMATES OF MOUNTAIN PLOVERS IN SOUTHERN PHILLIPS COUNTY, MONTANA

Information about the demography of declining species is especially relevant to their conservation and future recovery. Knowledge of survival rates and population size can be used to assess long-term viability and population trends, both of which are of interest to conservation biologists. We used capture–recapture techniques to study the demography of Mountain Plovers (Charadrius montanus Townsend) in southern Phillips County, Montana, USA, in 1995–2000. We used the robust design to estimate annual survival (ϕ), conditional capture (p and r) and recapture (c) probabilities, and the annual population size (N) in the presence of temporary emigration. The results support age-specific differences in annual survival that are a function of juvenile body mass and are correlated with the area occupied by prairie dogs. Body mass had a positive effect on juvenile survival; the slope coefficient for the additive effect of body mass on juvenile survival was 0.77 (95% ci = 0.25, 1.28) on a logit scale. A measure of p...

Age-Related Survival and Behavior of Snowy Plover Chicks

Abstract Abstract. Precocial young often experience high mortality prior to achieving flight, especially in the first days after hatching. We quantified relationships between chick age, survival, behavior, and response to natural and anthropogenic danger for the threatened Western Snowy Plover (Charadrius alexandrinus nivosus) in coastal northern California, USA. Plover chicks were most likely to die in the first three days of their 28-day prefledging period, especially on sandy ocean beaches compared to coarser substrates of river habitats. Chick survival in both habitats increased across the ∼120-day chick-rearing period. Improved survival of older chicks coincided with an age-related reduction in brooding and increased distance from the tending parent, which was not related to season. Lower survival of younger chicks was correlated with a tendency to lie motionless when approached by humans; nearly all older chicks responded to human approach by running to evade danger. Chicks of all ages were more likely to lie motionless when potential avian predators flew nearby. Age-dependent survival of Snowy Plover chicks paralleled a trend of increasing development, thermal independence from adults, and capability of evading predators.

DENSITY AND DIVERSITY OF OVERWINTERING BIRDS IN MANAGED FIELD BORDERS IN MISSISSIPPI

Abstract Grassland bird populations are sharply declining in North America. Changes in agricultural practices during the past 50 years have been suggested as one of the major causes of this decline. Field-border conservation practices encouraged by the U.S. Department of Agricultures National Conservation Buffer Initiative meet many of the needs of sustainable agriculture and offer excellent opportunities to enhance local grassland bird populations within intensive agricultural production systems. Despite the abundant information on avian use of, and reproductive success in, strip habitats during the breeding season, few studies have examined the potential value of field borders for wintering birds. We planted 89.0 km of field borders (6.1 m wide) along agricultural field edges on one-half of each of three row crop and forage production farms in northeastern Mississippi. We sampled bird communities along these field edges during February–March 2002 and 2003 using line-transect distance sampling and strip transects to estimate density and community structure, respectively. We used Program DISTANCE to estimate densities of Song (Melospiza melodia), Savannah (Passerculus sandwichensis), and other sparrows along bordered and non-bordered transects while controlling for adjacent plant community. Greater densities of several sparrow species were observed along most bordered transects. However, effects of field borders differed by species and adjacent plant community types. Diversity, species richness, and relative conservation value (a weighted index derived by multiplying species-specific abundances by their respective Partners in Flight conservation priority scores) were similar between bordered and non-bordered edges. Field borders are practical conservation tools that can be used to accrue multiple environmental benefits and enhance wintering farmland bird populations. Provision of wintering habitat at southern latitudes may influence population trajectories of short-distance migrants of regional conservation concern.

Estimation and Correction of Visibility Bias in Aerial Surveys of Wintering Ducks

Abstract Incomplete detection of all individuals leading to negative bias in abundance estimates is a pervasive source of error in aerial surveys of wildlife, and correcting that bias is a critical step in improving surveys. We conducted experiments using duck decoys as surrogates for live ducks to estimate bias associated with surveys of wintering ducks in Mississippi, USA. We found detection of decoy groups was related to wetland cover type (open vs. forested), group size (1–100 decoys), and interaction of these variables. Observers who detected decoy groups reported counts that averaged 78% of the decoys actually present, and this counting bias was not influenced by either covariate cited above. We integrated this sightability model into estimation procedures for our sample surveys with weight adjustments derived from probabilities of group detection (estimated by logistic regression) and count bias. To estimate variances of abundance estimates, we used bootstrap resampling of transects included in aerial surveys and data from the bias-correction experiment. When we implemented bias correction procedures on data from a field survey conducted in January 2004, we found bias-corrected estimates of abundance increased 36–42%, and associated standard errors increased 38–55%, depending on species or group estimated. We deemed our method successful for integrating correction of visibility bias in an existing sample survey design for wintering ducks in Mississippi, and we believe this procedure could be implemented in a variety of sampling problems for other locations and species.

INFLUENCE OF DROUGHT ON ANNUAL SURVIVAL OF THE MOUNTAIN PLOVER IN MONTANA

Abstract I used a robust design to model the influence of age, sex, climate conditions, and chick body mass on the annual survival of the Mountain Plover (Charadrius montanus) in north-central Montana from 1995–2006. I found evidence that chick age predicted body mass (i.e., log10 (mass) = 0.03 × age + 1.02) and subsequently modeled juvenile survival as a function of body mass. Juvenile survival was similar for both sexes and was positively influenced by body mass at capture. The predicted annual survival for a juvenile plover from date of hatching (10 g) was 0.06 (95% CI was 0.02, 0.15) and increased with body mass. Annual survival was similar for adults of both sexes and ranged from 0.74 to 0.96 yearly. There was a hint that male survival was higher than that of females, although this effect was weak. Adult survival was affected by a Palmer Modified Drought Index that measured local climate conditions and indicated that annual survival was highest during drought periods. Implications of this study include understanding the processes influencing annual survival in a declining species, providing a basis for long-term population projections, relating demographic processes to climate change, and increasing our knowledge of survival patterns among the Charadriidae.

MOUNTAIN PLOVER POPULATION RESPONSES TO BLACK-TAILED PRAIRIE DOGS IN MONTANA

Abstract We studied a local population of mountain plovers (Charadrius montanus) in southern Phillips County, Montana, USA, from 1995 to 2000 to estimate annual rates of recruitment rate (f) and population change (λ). We used Pradel models, and we modeled λ as a constant across years, as a linear time trend, as year-specific, and with an additive effect of area occupied by prairie dogs (Cynomys ludovicianus). We modeled recruitment rate (f) as a function of area occupied by prairie dogs with the remaining model structure identical to the best model used to estimate λ. Our results indicated a strong negative effect of area occupied by prairie dogs on both λ (slope coefficient on a log scale was −0.11; 95% CI was −0.17, −0.05) and f (slope coefficient on a logit scale was −0.23; 95% CI was −0.36, −0.10). We also found good evidence for a negative time trend on λ; this model had substantial weight (wi = 0.31), and the slope coefficient on the linear trend on a log scale was −0.10 (95% CI was −0.15, −0.05). Yearly estimates of λ were >1 in all years except 1999, indicating that the population initially increased and then stabilized in the last year of the study. We found weak evidence for year-specific estimates of λ; the best model with year-specific estimates had a low weight (wi = 0.02), although the pattern of yearly estimates of λ closely matched those estimated with a linear time trend. Insouthern Phillips County, the population trend of mountain plovers closely matched the trend in the area occupied by black-tailed prairie dogs. Black-tailed prairie dogs declined sharply in the mid-1990s in response to an outbreak of sylvatic plague, but their numbers have steadily increased since 1996 in concert with increases in plovers. The results of this study (1) increase our understanding of the dynamics of this population and how they relate to the area occupied by prairie dogs, and (2) will be useful for planning plover conservation in a prairie dog ecosystem.

THE INFLUENCE OF BODY CONDITION ON LOCAL APPARENT SURVIVAL OF SPRING MIGRANT SANDERLINGS IN COASTAL NORTH CAROLINA

Abstract Many shorebirds are long-distance migrants, and they depend upon widely spaced stopover sites for refueling during their annual migrations. Two competing hypotheses attempt to explain stopover duration: one predicts departure based on time minimization (time-selection hypothesis) and the other predicts departure on the basis of maximum energy gain (energy-selection hypothesis). During spring 1993, we tested these hypotheses during a mark-resight study of migrant Sanderlings (Calidris alba) at Portsmouth Island, North Carolina. We individually color-banded 204 Sanderlings and used capture-recapture methods to estimate local apparent survival during 10 five-day intervals from late April to mid-June. We found that survival rates were best modeled as a decreasing quadratic time trend; a linear time trend and period-specific survival rates received little support. We found no evidence that either body mass or a simple body condition index better explained survival rates. Our estimates of the 5-day local survival rates of Sanderlings at Portsmouth Island remained relatively high (ϕi > 0.80) through late May, after which they dropped rapidly as birds left the area. The period-specific conditional resighting probability was 0.39 (SE = 0.03). Our results do not provide strong support for either the time- or energy-selection hypotheses and hint that studies of migratory behavior need to be conducted even more intensively and across much larger regions in order to better understand the underlying factors. Influencia de la Condición Física sobre las Tasas de Residencia de Calidris alba durante la Migración de Primavera en la Costa de Carolina del Norte Resumen. Muchos playeros migran largas distancias y dependen de áreas ampliamente esparcidas para hacer escalas durante sus migraciones anuales. En estas áreas, los playeros reabastecen rápidamente sus reservas energéticas antes de partir hacia la próxima parada. Existen dos hipótesis principales para explicar la duración de cada escala: una predice que la duración de cada escala es en función de poder minimizar el tiempo (hipótesis de selección temporal) y la otra que el tiempo de escala es determinado sobre la base de maximizar la ganancia de energía (hipótesis de selección energética). Durante la primavera de 1993 pusimos a prueba estas hipótesis durante un estudio sobre captura-recaptura del playero Calidris alba en la Isla de Portsmouth, Carolina del Norte. Marcamos individualmente 204 playeros y usamos el método de captura-recaptura para estimar las tasas de residencia durante 10 intervalos de 5 días entre finales de abril y mediados de junio. Los modelos que mejor explicaron las tasas de residencia revelaron una tendencia cuadrática decreciente. Los datos no apoyaron modelos de tendencia lineal ni tasas de residencia período-específicas. No encontramos evidencia de que el peso corporal ni un índice simple de condición física contribuyesen a explicar mejor las tasas de residencia. Nuestras estimaciones de las tasas de residencia a 5-días para C. alba en la Isla de Portsmouth permanecieron relativamente altas (ϕi > 0.80) durante la segunda mitad de mayo, y disminuyeron rápidamente hasta que los playeros partieron del área. La probabilidad condicional de recuperación visual período-específica fue de 0.39 (EE = 0.03). Nuestros resultados no demostraron evidencia concluyente a favor de ninguna de las dos hipótesis (selección temporal, selección energética). Sugerimos que esta información resalta la necesidad de llevar a cabo estudios detallados a través de regiones geográficamente más amplias para poder entender qué factores explican mejor el comportamiento migratorio.

An Assessment of Factors Affecting Population Growth of the Mountain Plover

Effective conservation measures should target the most sensitive life history attributes of a species, assuming they are responsive to potential management actions. The Mountain Plover (Charadrius montanus) is a species of conservation concern with a patchy breeding distribution in western North America. Plovers prefer areas with short vegetation, bare ground, and disturbance for nesting. Current management tools, including grazing and burning, have been used to attract plovers and enhance nesting success. We used a stage-specific matrix model to study the influence of vital rates, e.g., juvenile and adult annual survival, on population growth rate in the Mountain Plover at two breeding sites in Colorado, South Park and Eastern Colorado, and one breeding site in Montana, USA. Our analysis was motivated by a need to 1) better understand the relationship between demographic rates and population growth rate, 2) assess current management tools for the plover by exploring their effect on population growth rate, and 3) identify areas of the plover’s population biology where additional demographic work is needed. Stochastic population growth rate was most influenced by adult survival, especially in Montana and South Park, Colorado (elasticities > 0.60), and was least influenced by first-year reproduction (all elasticities 0,60), et peu par la reproduction a la premiere annee (toutes les elasticites < 0,20). Les relations modelisees entre lambda et chaque taux demographique etaient faibles en general (r2 < 0,30), sauf en ce qui concerne le nombre d’œufs eclos par nid dans l’est du Colorado (r2 = 0,63), la survie des poussins a South Park (r2 = 0,40) et au Montana (r2 = 0,38), et la survie des adultes au Montana (r2 = 0,36). Nous avons examine l’augmentation prevue de lambda qui resulterait de l’augmentation de chaque taux demographique de sa valeur moyenne a sa valeur maximale observee dans nos simulations. La hausse de la survie des poussins et des adultes a mene a l’augmentation la plus grande de lambda, tandis que la hausse du nombre d’œufs eclos par nid a produit l’augmentation la plus faible de lambda. Nos resultats semblent indiquer que les futures mesures de conservation devraient viser l’augmentation de la survie des adultes ou des poussins plutot que l’augmentation du succes de nidification. Plus precisement, les taux de survie des adultes durant les periodes stationnaires, c.-a-d. l’ete et l’hiver, sont relativement eleves, de sorte que les mesures visant l’augmentation de la survie des adultes devraient peut-etre etre appliquees durant les periodes de migration. L’augmentation de la survie des poussins devrait etre une priorite d’action sur les aires de reproduction, parce que ce stade du cycle biologique est relativement court (< 3 mois) et qu’il offre des occasions de realiser des actions ciblees de gestion a court terme sur les aires de reproduction

Evaluation of an Aerial Survey to Estimate Abundance of Wintering Ducks in Mississippi

Abstract Researchers have successfully designed aerial surveys that provided precise estimates of wintering populations of ducks over large physiographic regions, yet few conservation agencies have adopted these probability-based sampling designs for their surveys. We designed and evaluated an aerial survey to estimate abundance of wintering mallards (Anas platyrhynchos), dabbling ducks (tribe Anatini) other than mallards, diving ducks (tribes Aythini, Mergini, and Oxyurini), and total ducks in western Mississippi, USA. We used design-based sampling of fixed width transects to estimate population indices (Î), and we used model-based methods to correct population indices for visibility bias and estimate population abundance (N̂) for 14 surveys during winters 2002–2004. Correcting for bias increased estimates of mallards, other dabbling ducks, and diving ducks by an average of 40–48% among all surveys and contributed 48–61% of the estimated variance of N̂. However, mean-squared errors were consistently less for N̂ than Î. Estimates of N̂ met our goals for precision (CV ≤ 15%) in 7 of 14 surveys for mallards, 5 surveys for other dabbling ducks, no surveys for diving ducks, and 10 surveys for total ducks. Generally, we estimated more mallards and other dabbling ducks in mid- and late winter (Jan–Feb) than early winter (Nov–Dec) and determined that population indices from the late 1980s were nearly 3 times greater than those from our study. We developed a method to display relative densities of ducks spatially as an additional application of survey data. Our study advanced methods of estimating abundance of wintering waterfowl, and we recommend this design for continued monitoring of wintering ducks in western Mississippi and similar physiographic regions.