Because secretive marsh birds are difficult to detect, population status and habitat use for these birds are not well known. We conducted repeated surveys for secretive marsh birds across 264 sites in the Upper Mississippi River and Great Lakes Joint Venture region to estimate abundance, occupancy, and detection probabilities during the 2008 and 2009 breeding seasons. We identified species groups based on observed species co-occurrences. Two species, least bittern Ixobrychus exilis and American bittern Botaurus lentiginosus, co-occurred with other species less often than expected by chance, and two species groups, rails (Virginia rail Rallus limicola and sora Porzana carolina) and open-water birds (pied-billed grebe Podilymbus podiceps, common moorhen Gallinula chloropus, and American coot Fulica americana; coots were only surveyed in 2009), co-occurred more often than expected by chance. These groupings were consistent between years. We then estimated the relation of these species and groups to landscape and local site characteristics by using zero-inflated abundance models that accounted for incomplete detection. At the landscape level (5-km radius), the amount of emergent herbaceous wetland was positively associated with least bittern occupancy, whereas the amount of woody wetland was negatively associated with least bittern, rail, and open-water bird occupancy. At the local level, habitat variables that were associated with abundance were not consistent among groups or between years, with the exception that both least bitterns and open-water birds had a strong positive association between abundance and water–vegetation interspersion. Land managers interested in marsh bird management or conservation may want to consider focusing efforts on landscapes with high amounts of emergent herbaceous wetland and low amounts of woody wetland, and managing for high amounts of water–vegetation interspersion within the wetland.
Throughout many arid lands of Africa, Australia and the United States, wildlife agencies provide water year-round for increasing game populations and enhancing biodiversity, despite concerns that water provisioning may favor species more dependent on water, increase predation, and reduce biodiversity. In part, understanding the effects of water provisioning requires identifying why and when animals visit water. Employing this information, by matching water provisioning with use by target species, could assist wildlife management objectives while mitigating unintended consequences of year-round watering regimes. Therefore, we examined if weather variables (maximum temperature, relative humidity [RH], vapor pressure deficit [VPD], long and short-term precipitation) and predator-prey relationships (i.e., prey presence) predicted water visitation by 9 mammals. We modeled visitation as recorded by trail cameras at Sevilleta National Wildlife Refuge, New Mexico, USA (June 2009 to September 2014) using generalized linear modeling. For 3 native ungulates, elk (Cervus Canadensis), mule deer (Odocoileus hemionus), and pronghorn (Antilocapra americana), less long-term precipitation and higher maximum temperatures increased visitation, including RH for mule deer. Less long-term precipitation and higher VPD increased oryx (Oryx gazella) and desert cottontail rabbits (Sylvilagus audubonii) visitation. Long-term precipitation, with RH or VPD, predicted visitation for black-tailed jackrabbits (Lepus californicus). Standardized model coefficients demonstrated that the amount of long-term precipitation influenced herbivore visitation most. Weather (especially maximum temperature) and prey (cottontails and jackrabbits) predicted bobcat (Lynx rufus) visitation. Mule deer visitation had the largest influence on coyote (Canis latrans) visitation. Puma (Puma concolor) visitation was solely predicted by prey visitation (elk, mule deer, oryx). Most ungulate visitation peaked during May and June. Coyote, elk and puma visitation was relatively consistent throughout the year. Within the diel-period, activity patterns for predators corresponded with prey. Year-round water management may favor species with consistent use throughout the year, and facilitate predation. Providing water only during periods of high use by target species may moderate unwanted biological costs.
The invasive red imported fire ant (Solenopsis invicta) has negatively affected a host of taxonomic groups throughout its acquired North American range. Many studies have hypothesized indirect trophic impacts, but few documented those impacts. We evaluated invertebrate abundance as a factor limiting juvenile survival of the endangered Attwater's prairie‐chicken (Tympanuchus cupido attwateri), and whether fire ants reduce invertebrate numbers and biomass. From 2009–2013, we monitored survival of Attwater's prairie‐chicken broods (n = 63) with radio telemetry during the first 2 weeks post‐hatch and collected daily invertebrate samples at brood sites. Broods located in areas with the highest median invertebrate count (338 invertebrates/25 sweeps) had a survival probability of 0.83 at 2 weeks post‐hatch compared to 0.07 for broods located in areas with the lowest median invertebrate count (18 invertebrates/25 sweeps). During 2011–2012, we evaluated the reduction of fire ants on invertebrate numbers and biomass by aerially treating areas with Extinguish Plus™ in an impact‐reference study design. Treated fields had 27% more individual invertebrates and 26% higher invertebrate biomass than reference fields. Our results clearly document that invertebrate abundance affects Attwater's prairie‐chicken brood survival and that fire ants may indirectly contribute to low brood survival by suppressing invertebrate abundance. We posit that within the fire ant's acquired North American range, fire ants are likely contributing to declines of other insectivorous species. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
Abstract. Robust models of wildlife population size, spatial distribution, and habitat relationships are needed to more effectively monitor endangered species and prioritize habitat conservation efforts. Remotely sensed data such as airborne laser altimetry (LiDAR) and digital color infrared (CIR) aerial photography combined with well-designed field studies can help fill these information voids. We used point count-based distance sampling survey data and LiDAR-fused CIR aerial photography to model density of the Golden-cheeked Warbler (Setophaga chrysoparia), an endangered songbird, on the 10 000-ha Balcones Canyonlands National Wildlife Refuge (BCNWR). We developed a novel set of candidate models to explain Golden-cheeked Warbler detection probability and density using habitat covariates characterizing vegetation structure, composition, and complexity as well as habitat fragmentation, topography, and human infrastructure. We had the most model support for covariates calculated using focal means representing a 3.2 ha territory size (100 m radius) vs. 1.8 and 7.0 ha territory sizes. Detection probability decreased with canopy cover and increased with topographic roughness. Golden-cheeked Warbler density increased with canopy cover, was highest at a 7:3 ratio of Ashe juniper (Juniperus ashei) to broadleaf tree canopy cover, and decreased with global solar radiation. Predicted warbler densities using 3 min point counts were similar to six estimates from independently collected warbler territory mapping on BCNWR with a mean difference of 6% and a Root Mean Squared Error of 1.88 males/40 ha. The total population size for BCNWR was estimated at 884 Golden-cheeked Warbler males (95% CI 662, 1206) and predicted densities across the refuge ranged from 0.0 to 0.50 male warblers per ha. On the basis of observed habitat relationships, we defined high quality habitat as having at least 60% canopy cover with Ashe juniper comprising 50-90% of the canopy. We estimated 48% of the area at BCNWR managed for Golden-cheeked Warblers was in high quality habitat conditions and identified patches within the lower habitat quality areas (14% of warbler management areas) that had the greatest potential to become high quality habitat with management. Our approach combined robust wildlife surveys with highly scalable remotely sensed data to examine habitat relationships, estimate population size, and identify existing areas of high quality habitat. This method can be applied to other species of conservation interest and can be used with multiple years of remotely sensed data to assess changes in habitat at local to regional scales.
Knowledge of the length of time spent at migratory stopover sites, or stopover duration, can help biologists estimate the total number of birds passing through a site, which in turn can be used to estimate population size. We estimated the stopover duration for 106 radiomarked pectoral sandpipers (Calidris melanotos) in the Lower Mississippi River Alluvial Valley (MAV) during fall migrations in 2001 and 2002. We estimated time-at-site-after-capture by tracking radiomarked birds daily to determine their time of departure from stopover sites. We used lengthbiased sampling and program DISTANCE to estimate stopover duration from time-at-site-after-capture. Our estimate of stopover duration for pectoral sandpipers in the MAV over all sites and both years was 10.0 days (95% CI = 8.2-11.7). Aerial telemetry relocations from 2002 indicated that many pectoral sandpipers used multiple stopover sites during their migration through the MAV, which suggested that the total time spent by pectoral sandpipers in the MAV during fall migration, or turnover rate, was longer than the stopover duration. Future research should focus on estimating the number of stopover sites used by pectoral sandpipers and determine whether other shorebird species use multiple sites as well. If shorebirds migrating through the MAV stay in the region for a period longer than the 10 days suggested by the Lower Mississippi Valley Joint Venture (LMVJV) Migratory Bird Science Team in their modeling of shorebird energetic requirements, then more habitat may be required by shorebirds during fall migration than the 2,000 ha the group calculated for the MAV. JOURNAL OF WILDLIFE MANAGEMENT 69(2):671-680; 2005
Dispersal events can affect the distribution, abundance, population structure, and gene flow of animal populations, but little is known about long‐distance movements due to the difficulty of tracking individuals across space. We documented the natal and breeding dispersal of shrubland birds among 13 study sites in a 1000 km2 area in southeastern Ohio. In addition, we radio‐marked and tracked 37 adult males of one shrubland specialist, the Yellow‐breasted Chat (Icteria virens). We banded 1925 juveniles and 2112 adults of nine shrubland species from 2002 to 2005. Of these, 33 (1.7%) juveniles were encountered in subsequent years (2003–2006) as adults (natal dispersal) and 442 (20.9%) birds initially banded as breeding adults were re‐encountered in subsequent years (breeding dispersal). Apparent survival of juvenile shrubland birds on their natal patches was 0.024 (95% CI 0.016–0.036). After accounting for the probability of detection, we found that 21% of birds banded as juveniles and recaptured as adults returned to their natal patches, whereas 78% of adult birds showed fidelity to the patch where they were originally captured. Moreover, natal dispersers tended to move farther than breeding dispersers (corrected natal median = 1.7 km ± 0.37; corrected breeding median = 0.23 km ± 0.10). We used our estimates of natal dispersal and annual apparent survival to estimate true survival at 0.11 (95% CI 0.07–0.18) for juveniles in their first year. However, this estimate was only applicable for birds dispersing within 7 km of their natal patches. Interpatch movements of radio‐marked Yellow‐breasted Chats were not uncommon, with 13 of 37 males located in more than one habitat patch. Overall, we observed low natal philopatry, but high adult site fidelity for shrubland birds in our study area. Considering the frequency of short‐distance movements observed (median = 531 m, range = 88–1045 m), clustering of patches within 1 km might facilitate use of shrubland habitat.
Resumen. las poblaciones de Euphagus carolinus han disminuido en un 90% desde la década del sesenta, posiblemente por la conversión de humedales arbolados a áreas agrícolas en el sureste de los estados unidos. debido a que el uso de hábitat por parte de E. carolinus durante la época no reproductiva no ha sido cuantificado, estimamos sus tasas de ocupación invernal en el valle aluvial bajo del Mississippi en relación con el tipo de hábitat (cuatro tipos de bosques de bajura y campos agrícolas adyacentes), la densidad de árboles, la cobertura del dosel y la cobertura de agua. en enero y febrero, censamos 89 sitios en ocho ocasiones en 2006, y 117 y 109 sitios en 10 ocasiones en 2007 y 2008, respectivamente. la ocupación de aves individuales, estimada a partir de su presencia o ausencia en un sitio, fue generalmente alta y mayor en 2006 (0.71) que en 2007 (0.43) y 2008 (0.37). la ocupación de las bandadas, estimada a partir de la presencia de 20 o más individuos, fue máxima en 2006 (0.46), mínima en 2007 (0.17) e intermedia en 2008 (0.30), posiblemente debido a las fluctuaciones en los niveles de agua entre años. la especie no se especializó tanto en el uso de hábitat como se esperaba; las características del hábitat no predijeron consistentemente la ocupación de individuos o bandadas. la ocupación de individuos aumentó con la cobertura del dosel en 2007 y la ocupación de bandadas disminuyó con la densidad de árboles en 2006. en 2008, la ocupación de individuos aumentó con la densidad de árboles y fue mayor en bosques húmedos de bajura (0.51) que en otros ambientes (0.31-0.35). Se necesita más investigación para determinar si la ausencia de especificidad de hábitat está ampliamente difundida y si posiblemente es el resultado de requerimientos alimenticios diversos durante la época no reproductiva. haBitat occupancy By RuSty BlackBiRdS winteRing in the loweR MiSSiSSippi alluVial Valley ocupación del hábitat de invierno por Euphagus carolinus en el Valle aluvial Bajo del MississippiAbstract. the Rusty Blackbird (Euphagus carolinus) has declined by 90% since the 1960s, possibly from conversions of forested wetlands in the southeastern u.S. to agriculture. Because its habitat use during the nonbreeding season had not been quantified, we estimated occupancy rates of Rusty Blackbirds wintering in the lower Mississippi alluvial Valley in relation to habitat type (four types of bottomland forest and adjacent agricultural fields), tree density, canopy cover, and water cover. in January and february, we surveyed 89 sites eight times during 2006, 117 and 109 sites 10 times during 2007 and 2008, respectively. occupancy of individual birds, estimated from their presence or absence at a site, was generally high and greater in 2006 (0.71) than during either 2007 (0.43) or 2008 (0.37). occupancy of flocks, estimated from presence or absence of ≥20 individuals, was highest in 2006 (0.46), lowest in 2007 (0.17), and intermediate in 2008 (0.30), possibly because of water levels fluctuating from year to year. Rusty Blackbirds were not ...
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