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At least 631 records · Page 35Linked to original sources
USGS1995

Northern Pintail ( Anas acuta )

The Northern Pintail is a medium-sized dabbling duck of slender, elegant lines and conservative plumage coloration. It is circumpolar in distribution and abundant in North America, with core nesting habitat in Alaska and the Prairie Pothole Region of southern Canada and the northern Great Plains. Breeders favor shallow wetlands interspersed throughout prairie grasslands or arctic tundra. An early fall migrant, the species arrives on wintering areas beginning in August, after wing molt, often forming large roosting and feeding flocks on open, shallow wetlands and flooded agricultural fields. The birds consume grains, marsh plant seeds, and aquatic invertebrates throughout the fall and winter. Northern Pintails are among the earliest nesting ducks in North America, beginning shortly after ice-out in many northern areas. Individuals form new pair bonds each winter but are highly promiscuous during the nesting season, with mated and unmated males often involved in vigorous, acrobatic Pursuit Flights. Annual nest success and productivity vary with water conditions, predation, and weather. Females build nests on the ground, often long distances from water. Only the female incubates; her mate leaves shortly after incubation begins. Ducklings hatch together in one day, follow the female to water after a day in the nest, and fledge by July or August. Adults and ducklings consume mainly aquatic invertebrates during the breeding season. Predators and farming operations destroy many thousands of Northern Pintail nests annually; farming has also greatly reduced the amount of quality nesting cover available. Winter habitats are threatened by water shortages, agricultural development, contamination, and urbanization. Periods of extended drought in prairie nesting regions have caused dramatic population declines, usually followed by periods of recovery. Over the long term, however, the continental population of Northern Pintails has declined significantly from 6 million birds in the early 1970s to less than 3 million in the late 1980s and early 1990s. However, new conservation measures, such as habitat restoration and enhancement of agricultural lands, as well as prudent harvest restrictions, suggest that Northern Pintails should have a secure future in North America.

Book chapter↗
USGS2025

Potential interactions between birds and floating photovoltaic solar energy: Spatially informed species vulnerabilities, techno-ecological risks, and sustainability trade-offs

Floating photovoltaics (floating solar panels; FPV) can reduce the negative impacts of solar energy development in terrestrial environments, but their effects on freshwater ecosystems remain poorly understood. We examined potential FPV interactions with avian biodiversity, using previously modeled technical potential of FPV in the northeastern United States. We developed a vulnerability index based on avian species’: (i) morphological traits, (ii) level of conservation concern, and (iii) habitat requirements. Using eBird participatory science data, we assessed the risk of FPV to 291 species of birds occurring at FPV-suitable waterbodies based on their vulnerability index and estimated relative abundance at each location. The greatest risk of FPVs to birds was associated with waterbodies near the Atlantic coast and Great Lakes, and most (80%) of these high-risk waterbodies were smaller waterbodies. Because the avian risk at FPV-suitable waterbodies was not correlated with estimated energy generation, reducing risk to birds might not require energy trade-offs. Moreover, avoiding FPV installations at waterbodies predicted to pose high risk to birds is likely to return social and recreational benefits while minimizing risk of biofouling. Our analysis provides a framework for proactively evaluating risk, reducing potential adverse impacts of FPV to birds, and identifying cobenefits of sustainable FPV siting across waterscapes.

Connecticut, Delaware, Maine, Maryland, Massachuse↗
USGS2010

Regional estimates of ecological services derived from U.S. Department of Agriculture conservation programs in the Mississippi Alluvial Valley

The Mississippi Alluvial Valley (MAV) is the Nation?s largest floodplain and this once predominantly forested ecosystem provided significant habitat for a diverse flora and fauna, sequestered carbon in trees and soil, and stored floodwater, sediments, and nutrients within the floodplain. This landscape has been substantially altered by the conversion of nearly 75% of the riparian forests, predominantly to agricultural cropland, with significant loss and degradation of important ecosystem services. Large-scale efforts have been employed to restore the forest and wetland resources and the U.S. Department of Agriculture (USDA) Wetlands Reserve Program (WRP) and Conservation Reserve Program (CRP) represent some of the most extensive restoration programs in the MAV. The objective of the WRP is to restore and protect the functions and values of wetlands in agricultural landscapes with an emphasis on habitat for migratory birds and wetland-dependent wildlife, protection and improvement of water quality, flood attenuation, ground water recharge, protection of native flora and fauna, and educational and scientific scholarship. The degree to which these conservation practices can restore ecosystem functions and services is not well known. This project was initiated to quantify existing ecological services derived from USDA conservation practices in the MAV as part of the USDA Conservation Effects Assessment Project, Wetlands Component (CEAP-Wetlands). The U.S. Geological Survey (USGS), in collaboration with the USDA Natural Resources Conservation Service, the USDA Farm Service Agency, the U.S. Fish and Wildlife Service, and Ducks Unlimited, collected data on soils, vegetation, nitrogen cycling, migratory birds, and amphibians from 88 different sites between 2006 and 2008. Results from restored WRP sites were compared to baseline data from active agricultural cropland (AG) to evaluate changes in ecosystem services.

Arkansas, Kentucky, Louisiana, Mississippi, Missou↗
USGS2015

Towards sustainable management of huntable migratory waterbirds in Europe

The EU Birds Directive and the African-Eurasian Waterbird Agreement provide an adequate legal framework for sustainable management of migratory waterbird populations. The main shortcoming of both instruments is that it leaves harvest decisions of a shared resource to individual Member States and Contracting Parties without providing a shared information base and mechanism to assess the impact of harvest and coordinate actions in relation to mutually agreed objectives. A recent update of the conservation status of waterbirds in the EU shows that almost half of the populations of species listed on Annex II of the Birds Directive have a declining short-term trend and over half of them are listed in Columns A and B of AEWA. This implies that their hunting could either only continue under the framework of an adaptive harvest management plan or their hunting should be regulated with the view of restoring them in favourable conservation status. We argue that a structured approach to decision-making (such as adaptive management) is needed, supported with adequate organisational structures at flyway scale. We review the experience with such an approach in North America and assess the applicability of a similar approach in the European context. We show there is no technical reason why adaptive harvest management could be not applied in the EU or even AEWA context. We demonstrate that an informed approach to setting allowable harvests does not require detailed demographic information. Essential to the process, however, are estimates of either the observed growth rate from a monitoring program or the growth rate expected under ideal conditions. In addition, periodic estimates of population size are needed, as well as either empirical information or reasonable assumptions about the form of density dependence. We show that such information exists for many populations, but improvements are needed to improve geographic coverage, reliability and timely data availability. We highlight the importance of the International Waterbird Census and specialised goose and seaduck monitoring in estimating population sizes and observed growth rate of the populations. We encourage further investments into the development of these schemes. We also recognise the importance of migration studies to improve our understanding of delineations of populations. We also highlight that, with a few exceptions, the available data does not allow the European Commission, competent authorities of the Members States or other AEWA Contracting Parties to assess levels of harvest and their sustainability and, therefore, regulate hunting accordingly. Therefore, we recommend that annual reporting on 2 harvest levels of waterbird populations would be gradually introduced in the EU and the AEWA region. We propose that future AEWA and EU action plans and management plans for Annex II species should apply the principles of adaptive harvest management framework and make provisions for setting up adequate monitoring and information management systems and organisational structures to manage the decision-making process. We suggest that internationally coordinated management structures are established to facilitate dialogue, learning and communication between stakeholders with different interests and cultural backgrounds.

Report↗
USGS2006

Does body size affect a bird's sensitivity to patch size and landscape structure?

Larger birds are generally more strongly affected by habitat loss and fragmentation than are smaller ones because they require more resources and thus larger habitat patches. Consequently, conservation actions often favor the creation or protection of larger over smaller patches. However, in grassland systems the boundaries between a patch and the surrounding landscape, and thus the perceived size of a patch, can be indistinct. We investigated whether eight grassland bird species with different body sizes perceived variation in patch size and landscape structure in a consistent manner. Data were collected from surveys conducted in 44 patches of northern tallgrass prairie during 1998–2001. The response to patch size was very similar among species regardless of body size (density was little affected by patch size), except in the Greater Prairie-Chicken ( Tympanuchus cupido ), which showed a threshold effect and was not found in patches smaller than 140 ha. In landscapes containing 0%–30% woody vegetation, smaller species responded more negatively to increases in the percentage of woody vegetation than larger species, but above an apparent threshold of 30%, larger species were not detected. Further analyses revealed that the observed variation in responses to patch size and landscape structure among species was not solely due to body size per se, but to other differences among species. These results indicate that a stringent application of concepts requiring larger habitat patches for larger species appears to limit the number of grassland habitats that can be protected and may not always be the most effective conservation strategy.

Condor↗
USGS2000

Estimates of population change in selected species of tropical birds using mark-recapture data

The population biology of tropical birds is known for a only small sample of species; especially in the Neotropics. Robust estimates of parameters such as survival rate and finite rate of population change (A) are crucial for conservation purposes and useful for studies of avian life histories. We used methods developed by Pradel (1996, Biometrics 52:703-709) to estimate A for 10 species of tropical forest lowland birds using data from a long-term (> 20 yr) banding study in Panama. These species constitute a ecologically and phylogenetically diverse sample. We present these estimates and explore if they are consistent with what we know from selected studies of banded birds and from 5 yr of estimating nesting success (i.e., an important component of A). A major goal of these analyses is to assess if the mark-recapture methods generate reliable and reasonably precise estimates of population change than traditional methods that require more sampling effort.

Book chapter↗
USGS2023

Pollinator conservation and climate science at the U.S. Geological Survey

Introduction Ecosystems—whether agricultural, urban, or natural—depend on pollinators, great and small. Pollinators in the form of bees, birds, butterflies, bats, and even moths provide vital, but often invisible services, from contributing to biodiverse terrestrial wildlife and plant communities to supporting healthy watersheds. Pollinator declines worldwide have been noted as land-use and climate changes occur on the landscape. This is alarming because up to 75 percent of crop species that are important for human food production depend on pollinators for production. Biodiversity of pollinators in the United States includes more than 4,000 species of insects, birds, and mammals. Pollinator species in the United States are in crisis based on broad-scale changes in land-use and climate. The Committee on the Status of Pollinators in North America summarized active and passive management alternatives to benefit pollinators and reduce their decline. Because assessment of pollinators in the United States has historically lagged behind other regions of the world, the Committee challenged the U.S. Geological Survey (USGS) and U.S. Fish and Wildlife Service (USFWS) to develop conservation plans, for pollinators, including quantification of the effects of climate change. As an example of the immediate need to focus efforts on pollinator conservation, Inouye and others cited the USFWS’s 2017 listing of the rusty-patched bumble bee ( Bombus affinis ) as Endangered under the U.S. Endangered Species Act (ESA) of 1973. Strategies are developed to accomplish pollinator conservation goals and the USGS is contributing scientific expertise toward those goals.

Fact Sheet↗
USGS2001

Evaluation of the major histocompatibility complex (Mhc) in cranes: applications to conservation efforts

Although there have been heated discussions concerning the relative importance of using Mhc diversity as a basis for selecting breeders in conservation projects, most parties agree that the genetic variability residual in an endangered species should be maintained through genetic management, if at all possible. Substantial evidence exists (particularly in birds) documenting the influences of specific Mhc haplotypes on disease outcome and also that those individuals which are heterozygous for Mhc alleles appear to have an advantage for survival over those that are homozygous. Thus, conservation of genetic variability of the Mhc is likely important for the preservation of fitness, especially in small breeding populations. More than half of the world's crane species are listed as endangered. Members of all 15 known species are represented among breeding animals for captive propagation at the International Crane Foundation (Wisconsin) and the USGS Patuxent Wildlife Research Center (Maryland). Collaborative multi-organization efforts and the availability of extensive pedigree records have allowed the study of Mhc variability in several species of cranes. We have found, for example, that Mhc diversity in the captive Florida sandhill crane (Grus canadensis pratensis) population appears high, whereas in the captive whooping crane (Grus americana), which has undergone a severe 'genetic bottleneck,? both the number of alleles and the levels of heterozygosity appear to be substantially reduced.

Book chapter↗
USGS2010

Trading off short-term and long-term risk: minimizing the threat of Laysan duck extinction from catastrophes and sea-level rise

Conservation of oceanic island species presents many ecological and logistical challenges. The Northwestern Hawaiian Islands (NWHI) include 300,000 km 2 of ocean waters and 10 groups of sub-tropical islands and atolls of high conservation value. Designated as Papahanaumokuakea Marine National Monument, the islands provide habitat for four endangered species of terrestrial birds. Despite their protected status, many of these species are faced with the ongoing threat of extinction due to stochastic catastrophes such as disease, invasive mammal introductions, tsunamis, and hurricanes. To reduce the risk that a single catastrophe would lead to extinction, managers propose to restore multiple "insurance" populations on islands currently unoccupied by these species to increase their range and overall numbers.

Hawai'i↗
USGS2021

Fishing gear performance nearshore is substantiated by spatial analyses

We estimated whether the fish assemblages nearshore represented by electrofishing and gillnetting indexed location of reservoirs in a river basin. We expected that location in the basin would reflect a multiplicity of factors that determine fish habitat and fish assemblage composition, and therefore also anticipated a correlation between fish species composition and spatial variables if the gear type reflected legitimate differences in fish assemblages. We collected 1.6 million fish of 129 species in 22 reservoirs of the Tennessee River basin, USA. Standardized electrofishing represented different aspects of the fish assemblages than standardized gillnetting. Nevertheless, the assemblages documented by each gear type were correlated with the spatial location of the reservoirs in the river basin. Thus, even as these gear types reflected different aspects of existing fish assemblages, they each tracked spatial differences, suggesting that they reflected standing fish assemblages. Our study supports the use of standardized boat electrofishing and gillnetting as proper means for monitoring fish assemblages at large spatial scales. Our results further suggest that a well-designed and standardized sampling protocol can in fact provide an informative bird’s eye view of fish assemblages at regional, national, or continental scales suitable for informing conservation programs.

Alabama, Georgia, Kentucky, Mississippi, North Car↗
USGS2019

Seasonal variation in environmental and behavioural drivers of annual-cycle habitat selection in a nearshore seabird

Aim Conservation of highly mobile species often requires identifying locations or time periods of elevated vulnerability. Since both extrinsic habitat conditions and intrinsic behavioural and energetic requirements contribute to habitat use at the landscape scale, identifying spatial or temporal foci for conservation intervention requires understanding how habitat needs and distributions vary across the annual cycle. Nearshore marine birds inhabit highly dynamic systems and have widely varying habitat needs among breeding, moult and non-breeding seasons, making them a useful case study for testing the relative contributions of individual resource requirements and environmental conditions in driving annual variation in distribution patterns. Location Northern Gulf of Mexico (USA). Methods We tracked Brown Pelicans using bird-borne GPS transmitters and used a combination of Hidden Markov Models and multivariate selectivity analysis to compare the characteristics of preferred resident habitats used throughout the annual cycle. Results Habitat selection was driven by dynamic oceanographic variables during all stages of the annual cycle. Key habitat characteristics varied between seasons, with particularly strong selection on high productivity, low temperature and low salinity during the breeding and post-breeding moult periods. The post-breeding moult also corresponded to a time of limited availability of preferred habitats, resulting in extensive overlap between breeding populations from different administrative planning areas. Main conclusions By incorporating seasonal variation in individual behaviour and resource requirements into our habitat models, we were able to identify the post-breeding moult as a period of high selectivity and restricted availability of preferred habitats for Brown Pelicans. Locations meeting preferred habitat criteria during the post-breeding period, particularly estuarine habitats with high productivity and low salinity, would therefore be high-value targets for management and restoration. Our analysis demonstrates the importance of accounting for both intrinsic and extrinsic temporal variation in evaluating habitat selection.

Alabama, Florida, Louisiana, Mississippi, Texas↗
USGS2024

Boom and bust: The effects of masting on seed predator range dynamics and trophic cascades

Aim Spatiotemporal variation in resource availability is a strong driver of animal distributions. In the northern hardwood and boreal forests of the northeastern United States, tree mast events provide resource pulses that drive the population dynamics of small mammals, including the American red squirrel ( Tamiasciurus hudsonicus ), a primary songbird nest predator. This study sought to determine whether mast availability ameliorates their abiotic limits, enabling red squirrel elevational distributions to temporarily expand and negatively impact high-elevation songbirds. Location Northeastern United States. Methods We used two independent datasets to evaluate our hypotheses. First, we fit a dynamic occupancy model using data from camera trap surveys to evaluate red squirrel distributional responses to pulses in the tree mast. We also assessed population responses using systematic auditory surveys analysed with an open-population binomial mixture model. Further, we used modelled red squirrel abundance in nest-survival models to evaluate whether their abundance is correlated with the daily nest survival of three songbird species. Results The tree mast provided a critical resource pulse that resulted in a two-fold increase in the annual elevational distribution of red squirrels. The elevational distribution of red squirrels ranged from a minimum of ~450 m (range: 663–1145 m asl) following two consecutive years without a masting event to a maximum of over 1000 m (range: 443–1545 m asl) after a large mast event. The daily nest survival of three songbird species tended to decline with an increase in the abundance of red squirrels. Main Conclusions Tree mast is a central biological phenomenon in many temperate and boreal forests. This study reveals how this resource pulse results in range changes in a small mammal that is both a seed and bird predator, as well as prey for many carnivores. Thus, understanding this phenomenon can inform the conservation and management of northern forests, including breeding songbirds.

Connecticut, Maine, Massachusetts, New Hampshire, ↗
USGS2014

Status of forest birds on Rota, Mariana Islands

The western Pacific island of Rota is the third largest human inhabited island in the Mariana archipelago, and is designated an Endemic Bird Area. Between 1982 and 2012, 12 point-transect distance sampling surveys were conducted to assess population status. Surveys did not consistently sample the entire island; thus, we used a ratio estimator to estimate bird abundances in strata not sampled during every survey. Occupancy models of the 2012 survey revealed general patterns of habitat use and detectability among 11 species that could be reliably modeled. The endangered Mariana crow ( Corvus kubaryi ) was dispersed around the periphery of the island in steep forested habitats. In contrast, the endangered Rota white-eye ( Zosterops rotensis ) was restricted to the high-elevation mesa. Precision of detection probabilities and occupancy estimates and effects of habitat types, sampling conditions, and specific observers varied considerably among species, indicating that more narrowly defined classifications and additional observer training may improve the accuracy of predictive modeling. Population estimates of five out of ten native bird species, including collared kingfisher ( Todiramphus chloris orii ), Mariana crow, Mariana fruit-dove ( Ptilinopus roseicapilla ), Micronesian myzomela ( Myzomela rubrata ), and white-throated ground-dove ( Gallicolumba xanthonura ) declined over the 30-year time series. The crow declined sharply to fewer than 200 individuals (upper 95% confidence interval). Trends increased for Micronesian starling ( Aplonis opaca ), rufous fantail ( Rhipidura rufifrons mariae ), and white tern ( Gygis alba ). Rota white-eye numbers declined from 1982 to the late 1990s, but returned to 1980s levels by 2012. The trend for the yellow bittern ( Ixobrychus sinensis ) was inconclusive. The alien Eurasian tree sparrow ( Passer montanus ) apparently increased in number despite an unreliable trend assessment. Declines were noted in the other two alien birds, black drongo ( Dicrurus macrocercus ) and island collared-dove ( Streptopelia bitorquata ). Total bird densities on Rota were similar to those on Saipan and Tinian, which were lower than densities on Aguiguan. Overall, bird trends on Rota declined, whereas trends observed for the same period on Saipan and Tinian were mixed, and trends on Aguiguan were stable to increasing. We identified several sampling design and protocol procedures that may improve the precision of occupancy, status, and trend assessments. Continued monitoring and demographic sampling are needed to understand why most bird species on Rota are declining, to identify the causative agents, and to assess effectiveness of conservation actions for rare species, especially the Mariana crow.

Marianas Islands↗
USGS2015

Special considerations for specimen collections that may be involved in law enforcement cases

Causes of mortality in wildlife include natural conditions—such as the viral, bacterial, and fungal diseases discussed in other chapters of this manual—and human intervention. Direct human intervention in wildlife deaths may be associated with individual human actions, such as gunshot or poisonings, or with institutions, such as wind farms or mining operations. Mortality that can be directly attributed to humans may be considered a crime based on the animal(s) affected and (or) the agent used. Wildlife laws were established to protect our nation’s wildlife resources and assist in conserving healthy populations of native wildlife. A variety of laws pertain to wildlife, such as the Migratory Bird Treaty Act, which makes it illegal, except as permitted, to capture, kill, or possess a portion or all of any migratory bird, a member of the group that includes the vast majority of wild birds present in the United States. Similar to pathogens that can spread unchecked through a wild population, a person or an institution that illegally kills wildlife may continue this practice indefinitely or until the illegal activities are detected and addressed. Convicting the perpetrator of a crime, however, requires that certain practices and procedures be followed so that a solid legal case can be constructed. As with any crime, investigation of the event is led by law enforcement personnel who are well-versed in the applicable laws, oversee the collection of evidence, and pursue persons or entities of interest. These individuals are uniquely qualified and trained to maintain the integrity of evidence, evaluate suspects to effectively prosecute the case, and effect the penalties of the law. The investigation of direct crimes against humans may involve teams of 5–10 law enforcement agents and specialists—each with a certain focus such as blood spatter, fingerprints, or ballistics—in processing a crime scene. In contrast, investigations of crimes against wildlife generally involve markedly fewer wildlife law enforcement agents, and in many instances of unlawful wildlife death, only one law enforcement agent is available to process an entire crime scene and work on a case. Thus, the assistance of individuals familiar with the geographical area, the endemic animal populations, and the local ecology can be very important for building an effective case. The aims of this chapter are to 1) help biologists or field personnel recognize the signs that indicate a crime may have been committed, and 2) to give readers a basic understanding of how a wildlife crime scene is processed. This chapter is not intended to give readers the tools to investigate a crime scene alone, but will hopefully make them a valuable asset to law enforcement agents who respond to the scene. An effectively processed case, resulting in prosecution of a suspect, supports the law as a deterrent to future acts that could endanger the conservation of wildlife.

Techniques and Methods↗
USGS2008

Avian movements and wetland connectivity in landscape conservation

The current conservation crisis calls for research and management to be carried out on a long-term, multi-species basis at large spatial scales. Unfortunately, scientists, managers, and agencies often are stymied in their effort to conduct these large-scale studies because of a lack of appropriate technology, methodology, and funding. This issue is of particular concern in wetland conservation, for which the standard landscape approach may include consideration of a large tract of land but fail to incorporate the suite of wetland sites frequently used by highly mobile organisms such as waterbirds (e.g., shorebirds, wading birds, waterfowl). Typically, these species have population dynamics that require use of multiple wetlands, but this aspect of their life history has often been ignored in planning for their conservation. We outline theoretical, empirical, modeling, and planning problems associated with this issue and suggest solutions to some current obstacles. These solutions represent a tradeoff between typical in-depth single-species studies and more generic multi-species studies. They include studying within- and among-season movements of waterbirds on a spatial scale appropriate to both widely dispersing and more stationary species; multi-species censuses at multiple sites; further development and use of technology such as satellite transmitters and population-specific molecular markers; development of spatially explicit population models that consider within-season movements of waterbirds; and recognition from funding agencies that landscape-level issues cannot adequately be addressed without support for these types of studies.

Conservation Biology↗
USGS2019

Conservation status of the world’s swan populations, Cygnus sp. and Coscoroba sp.: a review of current trends and gaps in knowledge

Recent estimates of the world’s swan Cygnus sp. populations indicate that there are currently between 1.5–1.6 million birds in 8 species, including the Coscoroba Swan Coscoroba coscoroba as an honorary swan. Monitoring programmes in Europe and North America indicate that most populations increased following the introduction of national and international legislation to protect the species during the early- to mid-20th century. A switch from feeding primarily on aquatic vegetation to foraging on farmland (especially high-energy arable crops) in winter during the second half of the 20th century, is also considered a contributing factor. Trumpeter Swans Cygnus buccinator famously increased from just 69 individuals known to exist in 1935 (although small numbers were missed) to c. 76,000 at the present time, and most of the northern hemisphere swan populations have continued to show increasing/stable trends over the last 20 years. The exception to this pattern is a decline since 1995 in the Northwest European Bewick’s Swan population, following an increase in its population size during the 1970s–1980s, which is now being addressed through implementation of an International Single Species Action Plan. A proposal to change enforcement regulations of the Migratory Bird Treaty Act in the United States is also of concern, as potentially undermining protection for Trumpeter Swans in North America, illustrating the importance of politics and legislation as well as on-the-ground measures for species conservation. Elsewhere, less is known about the trends and conservation status for swans in central and eastern Asia, though count and research programmes introduced in China, added to those underway in Japan and Korea, have recently greatly enhanced our knowledge of swan populations on the East Asian flyway. Trends for the Black Swan Cygnus atratus in Australia and for the Black-necked Swan Cygnus melancoryphus in South America are also poorly known, because of the large numbers involved for the former and a lack of coordinated counts across difficult terrain for the latter. These southern hemisphere species are considered vulnerable to water resource developments ( i.e . where diversion of water is shrinking wetlands), and to droughts associated with El Nino events and climate change. More extensive monitoring is therefore required to determine whether swan populations and species are stable, fluctuating or in decline.

Wildfowl↗
USGS2010

Grassland birds wintering at U.S. Navy facilities in southern Texas

Grassland birds have undergone widespread decline throughout North America during the past several decades. Causes of this decline include habitat loss and fragmentation because of conversion of grasslands to cropland, afforestation in the East, brush and shrub invasion in the Southwest and western United States, and planting of exotic grass species to enhance forage production. A large number of exotic plant species, including grasses, have been introduced in North America, but most research on the effects of these invasions on birds has been limited to breeding birds, primarily those in northern latitudes. Research on the effects of exotic grasses on birds in winter has been extremely limited. This is the first study in southern Texas to examine and compare winter bird responses to native and exotic grasslands. This study was conducted during a period of six years (2003–2009) on United States Navy facilities in southern Texas including Naval Air Station–Corpus Christi, Naval Air Station–Kingsville, Naval Auxiliary Landing Field Waldron, Naval Auxiliary Landing Field Orange Grove, and Escondido Ranch, all of which contained examples of native grasslands, exotic grasslands, or both. Data from native and exotic grasslands were collected and compared for bird abundance and diversity; ground cover, vegetation density, and floristic diversity; bird and vegetation relationships; diversity of insects and arachnids; and seed abundance and diversity. Effects of management treatments in exotic grasslands were evaluated by comparing numbers and diversity of birds and small mammals in mowed, burned, and control areas. To determine bird abundance and bird species richness, birds were surveyed monthly (December–February) during the winters of 2003–2008 in transects (100 meter × 20 meter) located in native and exotic grasslands distributed at all five U.S. Navy facilities. To compare vegetation in native and exotic grasslands, vegetation characteristics were measured during 2003–2008 in the same transects used for bird surveys and included five measures of ground cover, plus estimates of plant species richness, vegetation density (visual obstruction) at two different heights, and shrub numbers. These data, plus seasonal rainfall, were then used to evaluate components of variation in native and exotic grasslands. Relations between total bird numbers and bird species richness with environmental variation in native and exotic grasslands were compared. To compare diversity of arthropods in native and exotic grasslands, insects and arachnids were collected using three different methodologies (standardized sweep-net, random sweep-net, and pitfall traps) during four seasons, (2005–2006), at Naval Air Station–Corpus Christi, Naval Auxiliary Landing Field Waldron, and Naval Air Station–Kingsville. To compare seed abundance and diversity between native and exotic grasslands, seeds were collected for two winters (2004–2006) at Naval Air Station–Corpus Christi and Naval Air Station–Kingsville. To evaluate effects of management on grassland vertebrates, abundance and diversity of birds and small mammals were estimated and compared in exotic grasses subjected to mowing, burning, or no active management (control) for one full year (2008–2009). Observations were made of 1,044 birds of 30 species in grassland transects during five winters. The Savannah Sparrow ( Passerculus sandwichensis ) was the most common bird, which, with 644 detections, accounted for 63 percent of all individuals identified to species. Meadowlarks ( Sturnella spp. ) and Le Conte’s Sparrows ( Ammodramus leconteii ) were the second (10 percent) and third (7 percent) most abundant bird species, respectively. Six of the seven most abundant species detected in grasslands were grassland species, and their numbers accounted for 87 percent of all birds, but 20 of the 30 species (67 percent) that used grasslands were not grassland species. Seven species observed in grassland transects during the study were Species of Conservation Concern: Le Conte’s Sparrow, Sedge Wren ( Cistothorus platensis ), Grasshopper Sparrow ( Ammodramus savannarum ), Long-billed Curlew ( Numenius americanus ), Sprague’s Pipit ( Anthus spragueii ), Cassin’s Sparrow ( Aimophila cassinii ), and Loggerhead Shrike ( Lanius ludovicianus ). Native grasslands consistently supported greater bird species richness than exotic grasslands. In one winter, exotic grasslands supported more birds than native grasslands. Native grasslands were determined to have more forb cover, more bare ground, and greater plant species richness than exotic grasslands, whereas exotic grasslands were characterized by more grass cover and relatively greater vegetation density during dry years. Not only did these individual measures differ between native and exotic grasslands, but components of variation also differed. In native grasslands, grass density and cover contributed more to variation, whereas in exotic grasslands, non-grass vegetation was a greater component of variation. Total bird numbers and bird species richness in native grasslands were related to the principal component that contained a measure of litter cover. Total bird numbers and bird species richness in exotic grasslands indicated no significant relationships with any of the principal components of variation. The two most common insect orders in native grasslands were Hymenoptera and Coleoptera, which accounted for 42 percent of all insects. The two most common insect orders in exotic grasslands were Hemiptera and Homoptera, which accounted for about 80 percent of all insects. Insect family richness was greater in exotic grasslands than in native grasslands in two of four seasons. Proportions of arachnid families were similar in native and exotic grasslands, but arachnid family richness was greater in exotic grasslands than in native grasslands. Abundance of seeds was greater in exotic than in native grasslands. However, seed diversity was greater in native grasslands than in exotic grasslands. Among the three types of management (mowed, burned, and control) applied to exotic grasses, birds were most abundant in the mowed area. Sedge Wrens, however, were never encountered in mowed sites. Meadowlarks were similarly abundant in all treatments, but Le Conte’s Sparrows were detected only in the control (unmanaged) area. Hispid cotton rats ( Sigmodon hispidus ) accounted for 93 percent of all rodent captures, with the number of captures peaking December through February. Hispid cotton rat numbers and total rodent numbers were greatest in control and pre-burn areas, and lowest in the mowed area. Mammal diversity, however, was greatest in the mowed habitat. Native and exotic grasslands differed essentially in all categories (bird numbers and diversity, vegetation characteristics, components of variation, diversity of insects and arachnids, and seed abundance and diversity) used to measure and compare them. This indicates that fundamental ecosystem processes have been altered after native grasslands have undergone invasion and ultimate domination by exotic grass species. Future research in Texas grassland ecosystems is essential because: 1) Texas sustains more area in grasslands than any other state or province in the Central Flyway; 2) Texas serves as the winter destination or migration pathway for hundreds of species of birds, including winter residents and Neotropical migrants; 3) ecology, distribution, and numbers of grassland birds wintering in southern latitudes of the United States remains poorly understood; and 4) climate change threatens to further accelerate advances of invading grass species.

Open-File Report↗