Victoria J. Dreitz

ANNUAL SURVIVAL OF SNAIL KITES IN FLORIDA: RADIO TELEMETRY VERSUS CAPTURE-RESIGHTING DATA

We estimated annual survival of Snail Kites (Rostrhamus sociabilis) in Florida using the Kaplan-Meier estimator with data from 271 radio-tagged birds over a three-year period and capture-recapture (resighting) models with data from 1,319 banded birds over a six-year period. We tested the hypothesis that survival differed among three age classes using both data sources. We tested additional hypotheses about spatial and temporal variation using a combination of data from radio telemetry and single- and multistrata capture-recapture models. Results from these data sets were similar in their indications of the sources of variation in survival, but they differed in some parameter estimates. Both data sources indicated that survival was higher for adults than for juveniles, but they did not support delineation of a subadult age class. Our data also indicated that survival differed among years and regions for juveniles but not for adults. Estimates of juvenile survival using radio telemetry data were higher than estimates using capture-recapture models for two of three years (1992 and 1993). Ancillary evidence based on censored birds indicated that some mortality of radio-tagged juveniles went undetected during those years, resulting in biased estimates. Thus, we have greater confidence in our estimates of juvenile survival using capture-recapture models. Precision of estimates reflected the number of parameters estimated and was surprisingly similar between radio telemetry and single-stratum capture-recapture models, given the substantial differences in sample sizes. Not having to estimate resighting probability likely offsets, to some degree, the smaller sample sizes from our radio telemetry data. Precision of capture-recapture models was lower using multistrata models where region-specific parameters were estimated than using single-stratum models, where spatial variation in parameters was not taken into account.

Gravel-bed river floodplains are the ecological nexus of glaciated mountain landscapes

Gravel-bed rivers are disproportionately important to regional biodiversity, species interactions, connectivity, and conservation. Gravel-bed river floodplains in mountain landscapes disproportionately concentrate diverse habitats, nutrient cycling, productivity of biota, and species interactions. Although stream ecologists know that river channel and floodplain habitats used by aquatic organisms are maintained by hydrologic regimes that mobilize gravel-bed sediments, terrestrial ecologists have largely been unaware of the importance of floodplain structures and processes to the life requirements of a wide variety of species. We provide insight into gravel-bed rivers as the ecological nexus of glaciated mountain landscapes. We show why gravel-bed river floodplains are the primary arena where interactions take place among aquatic, avian, and terrestrial species from microbes to grizzly bears and provide essential connectivity as corridors for movement for both aquatic and terrestrial species. Paradoxically, gravel-bed river floodplains are also disproportionately unprotected where human developments are concentrated. Structural modifications to floodplains such as roads, railways, and housing and hydrologic-altering hydroelectric or water storage dams have severe impacts to floodplain habitat diversity and productivity, restrict local and regional connectivity, and reduce the resilience of both aquatic and terrestrial species, including adaptation to climate change. To be effective, conservation efforts in glaciated mountain landscapes intended to benefit the widest variety of organisms need a paradigm shift that has gravel-bed rivers and their floodplains as the central focus and that prioritizes the maintenance or restoration of the intact structure and processes of these critically important systems throughout their length and breadth.

Drought and cooler temperatures are associated with higher nest survival in Mountain Plovers

Native grasslands have been altered to a greater extent than any other biome in North America. The habitats and resources needed to support breeding performance of grassland birds endemic to prairie ecosystems are currently threatened by land management practices and impending climate change. Climate models for the Great Plains prairie region predict a future of hotter and drier summers with strong multiyear droughts and more frequent and severe precipitation events. We examined how fluctuations in weather conditions in eastern Colorado influenced nest survival of an avian species that has experienced recent population declines, the Mountain Plover (Charadrius montanus). Nest survival averaged 27.2% over a 7-yr period (n = 936 nests) and declined as the breeding season progressed. Nest survival was favored by dry conditions and cooler temperatures. Projected changes in regional precipitation patterns will likely influence nest survival, with positive influences of predicted declines in summer rainfall yet negative effects of more intense rain events. The interplay of climate change and land use practices within prairie ecosystems may result in Mountain Plovers shifting their distribution, changing local abundance, and adjusting fecundity to adapt to their changing environment. RESUME. Les prairies naturelles ont ete plus grandement modifiees que tout autre biome en Amerique du Nord. L’habitat et les ressources necessaires pour favoriser la performance reproductrice des oiseaux de prairie endemiques de ces ecosystemes sont actuellement menaces par les pratiques de gestion des terres et les changements climatiques imminents. Les modeles climatiques pour les prairies des Grandes Plaines prevoient des etes plus chauds et plus secs, des secheresses severes durant plusieurs annees et des evenements de precipitation plus frequents et intenses que ce qu’on observe presentement. Nous avons examine les effets des fluctuations des conditions meteorologiques dans l’est du Colorado sur la survie des nids chez une espece aviaire ayant subi un recent declin des populations, le Pluvier montagnard (Charadrius montanus). Le taux de survie des nids s’elevait a 27,2 % en moyenne sur une periode de 7 ans (n = 936 nids) et diminuait a mesure que progressait la saison de reproduction. La survie des nids etait superieure quand les conditions etaient seches et les temperatures fraiches. Les changements prevus dans les tendances regionales des precipitations influenceront vraisemblablement la survie des nids : tandis que la diminution des precipitations estivales prevue entrainera un effet positif sur la survie, les evenements de precipitation plus intenses prevus auront, quant a eux, un effet negatif. L’interaction des changements climatiques et des pratiques d’utilisation des sols dans les ecosystemes de prairie amenera peut-etre le Pluvier montagnard a modifier sa repartition, son abondance locale et sa fecondite pour s’adapter a l’environnement changeant.

Occupancy of Mountain Plover and Burrowing Owl in Colorado

Abstract Concern over the decline of grassland birds has spurred efforts to increase understanding of grassland bird–habitat relationships. Previous studies have suggested that black-tailed prairie dogs (Cynomys ludovicianus) provide important habitat for shortgrass prairie avifauna, such as mountain plover (Charadrius montanus) and western burrowing owl (Athene cunicularia hypugaea), although such studies are lacking in Colorado (USA). We used methods to estimate occupancy (ψ) of mountain plover and burrowing owl on prairie dog colonies and other shortgrass prairie habitats in eastern Colorado. Mountain plover occupancy was higher on prairie dog colonies (ψ = 0.50, 95% CI = 0.36–0.64) than on grassland (ψ = 0.07, 95% CI = 0.03–0.15) and dryland agriculture (ψ = 0.13, 95% CI = 0.07–0.23). Burrowing owl occupancy was higher on active prairie dog colonies (ψ = 0.80, 95% CI = 0.66–0.89) compared with inactive colonies (ψ = 0.23, 95% CI = 0.07–0.53), which in turn was much higher than on grassland (ψ = 0.01, 95% CI = 0.00–0.07) and dryland agriculture (ψ = 0.00, 95% CI = 0.00–0.00). Mountain plover occupancy also was positively correlated with increasing amounts of prairie dog colony in the landscape. Burrowing owl occupancy was negatively correlated with increasing amounts of prairie dog colony in the surrounding landscape. Our results suggest that actions to conserve mountain plovers and burrowing owls should incorporate land management to benefit prairie dogs. Because managing for specific colony attributes is difficult, alternative management that promotes heterogeneity may ensure that suitable habitat is available for the guild of grassland inhabitants.

Movements and home ranges of mountain plovers raising broods in three Colorado landscapes

Abstract We report movements and home-range sizes of adult Mountain Plovers (Charadrius montanus) with broods on rangeland, agricultural fields, and prairie dog habitats in eastern Colorado. Estimates of home range size (95% fixed kernel) were similar across the three habitats: rangeland (146.1 ha ± 101.5), agricultural fields (131.6 ha ± 74.4), and prairie dog towns (243.3 ha ± 366.3). Our minimum convex polygon estimates of home-range size were comparable to those on rangeland reported by Knopf and Rupert (1996). In addition, movements—defined as the distance between consecutive locations of adults with broods—were equivalent across habitats. However, our findings on prairie dog habitat suggest that home-range size for brood rearing may be related to whether the prairie dog habitat is in a complex of towns or in an isolated town.

Abundance and Density of Mountain Plover (Charadrius montanus) and Burrowing Owl (Athene cunicularia) in Eastern Colorado

ABSTRACT. Because of continental-scale declines of grassland birds over the past century, conservation agendas are focused on increasing understanding of grassland bird ecology and habitat associations. Shortgrass prairie is a unique grassland ecosystem maintained, in part, by Black-tailed Prairie Dogs (Cynomys ludovicianus). The Mountain Plover (Charadrius montanus) and western Burrowing Owl (Athene cunicularia hypugaea) are species of conservation concern known to be associated with prairie dog colonies. We estimated abundance of Mountain Plovers and Burrowing Owls in three habitats within the Colorado shortgrass prairie ecosystem—prairie dog colonies, grassland not occupied by prairie dogs, and dryland agriculture. Further, we investigated habitat associations of Mountain Plovers and Burrowing Owls at multiple landscape scales. We estimated 8,577 Mountain Plovers (95% CI: 7,511–35,130) and 3,554 Burrowing Owls (95% CI: 3,298–8,445) in eastern Colorado. Mountain Plover density on prairie dog colony plots ( = 2.26 birds per 100 ha, 95% CI: 2.15–5.13) was significantly higher than densities on either grassland ( = 0.23,95% CI: 0.17–1.76) or dryland-agriculture plots ( = 0.45,95% CI: 0.44–0.53). Burrowing Owl density on prairie dog colony plots ( = 3.04 birds per 100 ha, 95% CI: 2.82–6.92) was significantly higher than densities on either grassland ( = 0.044, 95% CI: 0.041–0.12) or dryland-agriculture plots (no Burrowing Owls detected). Our results suggest that increased prairie dog colonies would positively influence the abundance of Mountain Plover and Burrowing Owl.

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

MONITORING LOW DENSITY AVIAN POPULATIONS: AN EXAMPLE USING MOUNTAIN PLOVERS

Abstract Declines in avian populations highlight a need for rigorous, broad-scale monitoring programs to document trends in avian populations that occur in low densities across expansive landscapes. Accounting for the spatial variation and variation in detection probability inherent to monitoring programs is thought to be effort-intensive and time-consuming. We determined the feasibility of the analytical method developed by Royle and Nichols (2003), which uses presence-absence (detection-nondetection) field data, to estimate abundance of Mountain Plovers (Charadrius montanus) per sampling unit in agricultural fields, grassland, and prairie dog habitat in eastern Colorado. Field methods were easy to implement and results suggest that the analytical method provides valuable insight into population patterning among habitats. Mountain Plover abundance was highest in prairie dog habitat, slightly lower in agricultural fields, and substantially lower in grassland. These results provided valuable insight to focus future research into Mountain Plover ecology and conservation.

EFFECTS OF NATAL DEPARTURE AND WATER LEVEL ON SURVIVAL OF JUVENILE SNAIL KITES (ROSTRHAMUS SOCIABILIS) IN FLORIDA

Abstract Survival rate from fledging to breeding, or juvenile survival, is an important source of variation in lifetime reproductive success in birds. Therefore, determining the relation-ship between juvenile survival and environmental factors is essential to understanding fitness consequences of reproduction in many populations. With increases in density of individuals and depletion of food resources, quality of most habitats deteriorates during the breeding season. Individuals respond by dispersing in search of food resources. Therefore, to understand the influence of environmental factors on juvenile survival, it is also necessary to know how natal dispersal influences survival of juveniles. We examined effects of various environmental factors and natal dispersal behavior on juvenile survival of endangered Snail Kites (Rostrhamus sociabilis) in central and southern Florida, using a generalized estimating equations (GEEs) approach and model selection criteria. Our results suggested yearly effects and an influence of age and monthly minimum hydrologic levels on juvenile Snail Kite survival. Yearly variation in juvenile survival has been reported by other studies, and other reproductive components of Snail Kites also exhibit such variation. Age differences in juvenile survival have also been seen in other species during the juvenile period. Our results demonstrate a positive relationship between water levels and juvenile survival. We suggest that this is not a direct linear relationship, such that higher water means higher juvenile survival. The juvenile period is concurrent with onset of the wet season in the ecosystem we studied, and rainfall increases as juveniles age. For management purposes, we believe that inferences suggesting increasing water levels during the fledging period will increase juvenile survival may have short-term benefits but lead to long-term declines in prey abundance and possibly wetland vegetation structure.

Extending Conifer Removal and Landscape Protection Strategies from Sage-grouse to Songbirds, a Range-Wide Assessment ☆

ABSTRACT Recent and unprecedented scale of greater sage-grouse (Centrocercus urophasianus) conservation in the American West enables assessment of community-level benefits afforded to other sagebrush-obligate species. We use North American Breeding Bird Survey (BBS) count data and machine-learning to assess predictors influencing spatial distribution and abundance of three sagebrush-obligate songbirds (Brewers sparrow [Spizella breweri], sagebrush sparrow [Artemisiospiza nevadensis], and sage thrasher [Oreoscoptes montanus]). We quantified co-occurrence of songbird abundance with sage-grouse lek distributions using point pattern analyses and evaluated the concurrence of songbird abundance within sage-grouse habitat restoration and landscape protection. Sagebrush land-cover predictors were positively associated with the abundance of each songbird species in models that explained 16–37% of variation in BBS route level counts. Individual songbird models identified an apparent 40% threshold in sagebrush land-cover, over which songbird abundances nearly doubled. Songbird abundances were positively associated with sage-grouse distributions (P b 0.01); range-wide, landscapes supporting N 50% of males on leks also harbored 13–19% higher densities of songbirds compared with range-wide mean densities. Eighty-five percent of the conifer removal conducted through the Sage Grouse Initiative coincided with high to moderate Brewers sparrow abundance. Wyomings landscape protection (i.e., “core area”) strategy for sage-grouse encompasses half the high to moderate abundance sagebrush sparrow and sage thrasher populations. In the Great Basin half the high to moderate abundance sagebrush sparrow and sage thrasher populations coincide with sage-grouse Fire and Invasive Assessment Tool priorities, where conservation actions are being focused in an attempt to reduce the threat of wildfire and invasive plants. Our work illustrates spatially targeted actions being implemented ostensibly for sage-grouse largely overlap high abundance centers for three sagebrush obligate passerines and are likely providing significant conservation benefits for less well-known sagebrush songbirds and other sagebrush-associated wildlife.