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USGS2010

Assessing allowable take of migratory birds

Legal removal of migratory birds from the wild occurs for several reasons, including subsistence, sport harvest, damage control, and the pet trade. We argue that harvest theory provides the basis for assessing the impact of authorized take, advance a simplified rendering of harvest theory known as potential biological removal as a useful starting point for assessing take, and demonstrate this approach with a case study of depredation control of black vultures (Coragyps atratus) in Virginia, USA. Based on data from the North American Breeding Bird Survey and other sources, we estimated that the black vulture population in Virginia was 91,190 (95% credible interval = 44,520?212,100) in 2006. Using a simple population model and available estimates of life-history parameters, we estimated the intrinsic rate of growth (rmax) to be in the range 7?14%, with 10.6% a plausible point estimate. For a take program to seek an equilibrium population size on the conservative side of the yield curve, the rate of take needs to be less than that which achieves a maximum sustained yield (0.5 x rmax). Based on the point estimate for rmax and using the lower 60% credible interval for population size to account for uncertainty, these conditions would be met if the take of black vultures in Virginia in 2006 was < 3,533 birds. Based on regular monitoring data, allowable harvest should be adjusted annually to reflect changes in population size. To initiate discussion about how this assessment framework could be related to the laws and regulations that govern authorization of such take, we suggest that the Migratory Bird Treaty Act requires only that take of native migratory birds be sustainable in the long-term, that is, sustained harvest rate should be < rmax. Further, the ratio of desired harvest rate to 0.5 x rmax may be a useful metric for ascertaining the applicability of specific requirements of the National Environmental Protection Act.

Journal of Wildlife Management↗

USGS2012

Weather effects on avian breeding performance and implications of climate change

The influence of recent climate change on the world’s biota has manifested broadly, resulting in latitudinal range shifts, advancing dates of arrival of migrants and onset of breeding, and altered community relationships. Climate change elevates conservation concerns worldwide because it will likely exacerbate a broad range of identified threats to animal populations. In the past few decades, grassland birds have declined faster than other North American avifauna, largely due to habitat threats such as the intensification of agriculture. We examine the effects of local climatic variations on the breeding performance of a bird endemic to the shortgrass prairie, the Lark Bunting ( Calamospiza melanocorys ) and discuss the implications of our findings relative to future climate predictions. Clutch size, nest survival, and productivity all positively covaried with seasonal precipitation, yet relatively intense daily precipitation events temporarily depressed daily survival of nests. Nest survival was positively related to average temperatures during the breeding season. Declining summer precipitation may reduce the likelihood that Lark Buntings can maintain stable breeding populations in eastern Colorado although average temperature increases of up to 38C (within the range of this study) may ameliorate declines in survival expected with drier conditions. Historic climate variability in the Great Plains selects for a degree of vagility and opportunism rather than strong site fidelity and specific adaptation to local environments. These traits may lead to northerly shifts in distribution if climatic and habitat conditions become less favorable in the drying southern regions of the Great Plains. Distributional shifts in Lark Buntings could be constrained by future changes in land use, agricultural practices, or vegetative communities that result in further loss of shortgrass prairie habitats.

Colorado↗

USGS1991

Reproductive outcomes in colonial fish-eating birds: A biomarker for developmental toxicants in Great Lakes food chains: I. Historical and ecotoxicological perspectives

Colonial fish-eating birds have been used as convenient model populations in which to study the impact of chronic exposure to complex mixtures of persistent lipophilic environmental contaminants within the Great Lakes ecosystem. To date, published reports of contaminant-induced adverse reproductive outcomes exist for six species. We briefly review the studies of the herring gull ( Larus argentatu s), Forster's tern ( Sterna forsteri ), and the double-crested cormorant ( Phalacrocorax auritus ) to illustrate the use of reproductive outcomes in fish-eating birds as a biomarkerfor developmental toxicants in Great Lakes food chains. We discuss the management implications of using various species for such purposes. We recommend that cormorants be used more extensively in biomonitoring programs to measure exposure and effects of polyhalogenated aromatic hydrocarbons and other contaminants in aquatic food chains in the Great Lakes.

Great Lakes↗

USGS2008

Releases of whooping cranes to the Florida nonmigratory flock: a structured decision-making approach: report to the International Whooping Crane Recovery Team, September 22, 2008

We used a structured decision-making approach to inform the decision of whether the Florida Fish and Wildlife Conservation Commission should request of the International Whooping Crane Recovery Team that additional whooping crane chicks be released into the Florida Non-Migratory Population (FNMP). Structured decision-making is an application of decision science that strives to produce transparent, replicable, and defensible decisions that recognize the appropriate roles of management policy and science in decision-making. We present a multi-objective decision framework, where management objectives include successful establishment of a whooping crane population in Florida, minimization of costs, positive public relations, information gain, and providing a supply of captive-reared birds to alternative crane release projects, such as the Eastern Migratory Population. We developed models to predict the outcome relative to each of these objectives under 29 different scenarios of the release methodology used from 1993 to 2004, including options of no further releases and variable numbers of releases per year over the next 5-30 years. In particular, we developed a detailed set of population projection models, which make substantially different predictions about the probability of successful establishment of the FNMP. We used expert elicitation to develop prior model weights (measures of confidence in population model predictions); the results of the population model weighting and modelaveraging exercise indicated that the probability of successful establishment of the FNMP ranged from 9% if no additional releases are made, to as high as 41% with additional releases. We also used expert elicitation to develop weights (relative values) on the set of identified objectives, and we then used a formal optimization technique for identifying the optimal decision, which considers the tradeoffs between objectives. The optimal decision was identified as release of 3 cohorts (24 birds) per year over the next 10 years. However, any decision that involved release of 1-3 cohorts (8-24 birds) per year over the next 5 to 20 years, as well as decisions that involve skipping releases in every other year, performed better in our analysis than the alternative of no further releases. These results were driven by the relatively high objective weights that experts placed on the population objective (i.e., successful establishment of the FNMP) and the information gain objective (where releases are expected to accelerate learning on what was identified as a primary uncertainty: the demographic performance of wild-hatched birds). Additional considerations that were not formally integrated into the analysis are also discussed.

Florida↗

USGS2019

Impacts to wildlife of wind energy siting and operation in the United States

Electricity from wind energy is a major contributor to the strategy to reduce greenhouse gas emissions from fossil fuel use and thus reduce the negative impacts of climate change. Wind energy, like all power sources, can have adverse impacts on wildlife. After nearly 25 years of focused research, these impacts are much better understood, although uncertainty remains. In this report, we summarize positive impacts of replacing fossil fuels with wind energy, while describing what we have learned and what remains uncertain about negative ecological impacts of the construction and operation of land-based and offshore wind energy on wildlife and wildlife habitat in the U.S. Finally, we propose research on ways to minimize these impacts. TO SUMMARIZE: 1 Environmental and other benefits of wind energy include near-zero greenhouse gas emissions, reductions of other common air pollutants, and little or no water use associated with producing electricity from wind energy. Various scenarios for meeting U.S. carbon emission reduction goals indicate that a four- to five-fold expansion of land-based wind energy from the current 97 gigawatts (GW) by the year 2050 is needed to minimize temperature increases and reduce the risk of climate change to people and wildlife. 2 Collision fatalities of birds and bats are the most visible and measurable impacts of wind energy production. Current estimates suggest most bird species, especially songbirds, are at low risk of population-level impacts. Raptors as a group appear more vulnerable to collisions. Population-level impacts on migratory tree bats are a concern, and better information on population sizes is needed to evaluate potential impacts to these species. Although recorded fatalities of cave-dwelling bat species are typically low at most wind energy facilities, additional mortality from collisions is a concern given major declines in these species due to white-nose syndrome (WNS). Assessments of regional and cumulative fatality impacts for birds and bats have been hampered by the lack of data from areas with a high proportion of the nation’s installed wind energy capacity. Efforts to expand data accessibility from all regions are underway, and this greater access to data along with improvements in statistical estimators should lead to improved impact assessments. 3 Habitat impacts of wind energy development are difficult to assess. An individual wind energy facility may encompass thousands of acres, but only a small percentage of the landscape within the project area is directly transformed. If a project is sited in previously undisturbed habitat, there is concern for indirect impacts, such as displacement of sensitive species. Studies to date indicate displacement of some species, but the long-term population impacts are unknown. 4 Offshore wind energy development in the U.S. is just beginning. Studies at offshore wind facilities in Europe indicate some bird and marine mammal species are displaced from project areas, but substantial uncertainty exists regarding the individual or population-level impacts of this displacement. Bird and bat collisions with offshore turbines are thought to be less common than at terrestrial facilities, but currently the tools to measure fatalities at offshore wind energy facilities are not available. The wind energy industry, state and federal agencies, conservation groups, academia, and scientific organizations have collaborated for nearly 25 years to conduct the research needed to improve our understanding of risk to wildlife and to avoid and minimize that risk. Efforts to reduce the uncertainty about wildlife risk must keep up withthe pace and scale of the need to reduce carbon emissions. This will require focusing our research priorities and increasing the rate at which we incorporate research results into the development and validation of best practices for siting and operating wind energy facilities.

Issues in Ecology↗

USGS2015

New summer areas and mixing of two greater sandhill crane populations in the Intermountain West

Population delineation throughout the annual life cycle for migratory birds is needed to formulate regional and national management and conservation strategies. Despite being well studied continentally, connectivity of sandhill crane Grus canadensis populations throughout the western portion of their North American range remains poorly described. Our objectives were to 1) use global positioning system satellite transmitter terminals to identify summer distributions for the Lower Colorado River Valley Population of greater sandhill cranes Grus canadensis tabida and 2) determine whether intermingling occurs among any of the western greater sandhill crane populations: Rocky Mountain Population, Lower Colorado River Valley Population, and Central Valley Population. Capture and marking occurred during winter and summer on private lands in California and Idaho as well as on two National Wildlife Refuges: Cibola and Sonny Bono Salton Sea National Wildlife Refuges. A majority of marked greater sandhill cranes summered in what is established Lower Colorado River Valley Population breeding areas in northeastern Nevada and southwestern Idaho. A handful of greater sandhill cranes summered outside of traditional breeding areas in west-central Idaho around Cascade Reservoir near Donnelly and Cascade, Idaho. For example, a greater sandhill crane colt captured near Donnelly in July 2014 survived to winter migration and moved south to areas associated with the Rocky Mountain Population. The integration of the greater sandhill crane colt captured near Donnelly provides the first evidence of potential intermingling between the Lower Colorado River Population and Rocky Mountain Population. We suggest continued marking and banding efforts of all three western populations of greater sandhill cranes will accurately delineate population boundaries and connectivity and inform management decisions for the three populations.

Arizona, California, Idaho↗

USGS1995

Abundance, distribution and population status of Marbled Murrelets in Alaska

Ship-based surveys conducted throughout Alaska during the 1970's and 1980's, and more recent small boat surveys conducted in the northern Gulf of Alaska, suggest that about 280,000 murrelets reside in Alaska during summer. Most Marbled Murrelets are concentrated offshore of large tracts of coastal coniferous forests in southeast Alaska, Prince William Sound, and the Kodiak Archipelago. About 1-3 percent of murrelets breed wholly outside of forested areas in Alaska, and these presumably all nest on the ground. At sea, murrelets tend to occupy sheltered waters of bays, fiords, and island straits, and often aggregate near large river outflows or tide rips. Small boat surveys of Prince William Sound and Christmas Bird Count trends suggest that Marbled Murrelet populations in Alaska declined by about 50 percent between 1972 and 1992. Population declines may have resulted from cumulative effects of oil pollution, gill netting, logging of old-growth breeding habitat, and natural changes in the marine environment. The Exxon Valdez oil spill killed an estimated 8,400 murrelets in 1989, or about 3 percent of the Alaska population. The toll from chronic pollution is unknown. About 3300 murrelets (89 percent adult) die annually in fishing nets in Alaska - a sustained adult mortality rate of 1.5 percent per annum. The extent or effect on murrelets of logging in Alaska are unknown. While only 7 percent of the old-growth has been harvested in the Tongass National Forest, about 40 percent of the highly productive old-growth in the forest has already been logged. A decline in forage fish populations in the Gulf of Alaska during the last 20 years may account for reduced breeding success and population size of several seabird species, including murrelets. Murrelet populations should be sensitive to small increases in adult mortality from the above factors because production by murrects is low and must therefore be balanced by a low annual adult mortality rate.

Alaska↗

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↗

USGS2004

Cormorant predation and the population dynamics of walleye and yellow perch in Oneida Lake

Double-crested Cormorants ( Phalacrocorax auritus ) increased dramatically in North America during the 1990s, providing the opportunity to study the effects of an increase of a top predator on an existing predator-prey system. In Oneida Lake, New York, USA, Double-crested Cormorants were first observed nesting in 1984 and had increased to over 360 nesting pairs by 2000. Concomitant with this increase in piscivorous birds was a decrease in the adult walleye ( Stizostedion vitreum ) and yellow perch ( Perca flavescens ) populations. Analysis of a 40-yr data series shows higher mortality of subadults (age 1-2 yr perch and age 1-3 yr walleye) for both species in the 1990s compared to the previous three decades. Cormorant diet was investigated from 1995 to 2000 using a combination of cast pellets, regurgitants, and stomach analysis. Walleye and yellow perch were a major portion of the cormorant diet during these years (40-82% by number). The number of subadult walleye and yellow perch consumed by cormorants suggests that the increase in subadult mortality can be explained by predation from cormorants. Mean mortality rates of adult percids attributed to cormorant predation were 1.1% per year for walleye and 7.7% per year for yellow perch. Our analysis suggests that predation by cormorants on subadult percids is a major factor contributing to the decline in both the walleye and the yellow perch populations in Oneida Lake. Other ecosystem changes (zebra mussels, lower nutrient loading, decrease in alternate prey) are not likely explanations because the potential mechanisms involved are not consistent with auxiliary data from the lake and would not affect subadult mortality. The likely impact of bird predation on percid populations in Oneida Lake occurs because cormorants feed on larger fish that are beyond the size range where compensatory mechanisms are important.

New York↗

USGS2014

Effects of satellite transmitters on captive and wild mallards

Satellite telemetry has become a leading method for studying large-scale movements and survival in birds, yet few have addressed potential effects of the larger and heavier tracking equipment on study subjects. We simultaneously evaluated effects of satellite telemetry equipment on captive and wild mallards ( Anas platyrhynchos ) to assess impacts on behavior, body mass, and movement. We randomly assigned 55 captive ducks to one of 3 treatment groups, including a standard body harness group, a modified harness group, and a control group. Ducks in the control group were not fitted with equipment, whereas individuals in the other 2 groups were fitted with dummy transmitters attached with a Teflon ribbon harness or with a similar harness constructed of nylon cord. At the conclusion of the 14-week captive study, mean body mass of birds in the control group was 40–105 g (95% CI) greater than birds with standard harnesses, and 28–99 g (95% CI) greater than birds with modified harnesses. Further, results of focal behavior observations indicated ducks with transmitters were less likely to be in water than control birds. We also tested whether movements of wild birds marked with a similar Teflon harness satellite transmitter aligned with population movements reported by on-the-ground observers who indexed local abundances of mid-continent mallards throughout the non-breeding period. Results indicated birds marked with satellite transmitters moved concurrently with the larger unmarked population. Our results have broad implications for field research and suggest that investigators should consider potential for physiological and behavioral effects brought about by tracking equipment. Nonetheless, results from wild ducks indicate satellite telemetry has the potential to provide useful movement data.

Wildlife Society Bulletin↗

USGS1992

The relationship between annual survival rate and migration distance in mallards: An examination of the time-allocation hypothesis for the evolution of migration

Predictions of the time-allocation hypothesis were tested with several a posteriori analyses of banding data for the mallard (Anas platyrhynchos). The time-allocation hypothesis states that the critical difference between resident and migrant birds is their allocation of time to reproduction on the breeding grounds and survival on the nonbreeding grounds. Residents have higher reproduction and migrants have higher survival. Survival and recovery rates were estimated by standard band-recovery methods for banding reference areas in the central United States and central Canada. A production-rate index was computed for each reference area with data from the U.S. Fish and Wildlife Service May Breeding Population Survey and July Production Survey. An analysis of covariance was used to test for the effects of migration distance and time period (decade) on survival, recovery, and production rates. Differences in migration chronology were tested by comparing direct-recovery distributions for different populations during the fall migration. Differences in winter locations were tested by comparing distributions of direct recoveries reported during December and January. A strong positive relationship was found between survival rate, and migration distance for 3 of the 4 age and sex classes. A weak negative relationship was found between recovery rate and migration distance. No relationship was found between production rate and migration distance. During the fall migration, birds from the northern breeding populations were located north of birds from the southern breeding populations. No pattern could be found in the relative locations of breeding and wintering areas. Although our finding that survival rate increased with migration distance was consistent with the time-allocation hypothesis, our results on migration chronology and location of wintering areas were not consistent with the mechanism underlying the time-allocation hypothesis. Neither this analysis nor other recent studies of life-history characteristics of migratory and resident birds supported the timeallocation hypothesis.

Canadian Journal of Zoology↗

USGS2016

Eastern Whip-poor-wills (Antrostomus vociferus) are positively associated with low elevation forest In the central Appalachians

Populations of the Eastern Whip-poor-will ( Antrostomus vociferus ) are thought to be declining because of a range of potential factors including habitat loss, pesticide use, and predation. However, this species is nocturnal and, as a consequence, it is poorly studied, and its population status is not well assessed by traditional diurnal bird surveys. We used nocturnal road surveys to study habitat associations and distribution of Eastern Whip-poor-wills to better understand and contextualize their population status and to provide a framework for subsequent research and management. We used occupancy models to associate presence of Eastern Whip-poor-wills with habitat characteristics. Global models with habitat associations at a radius of 1600 m (1.0-ha area) were the best supported by the data, suggesting that this was the scale at which the species responded to the habitat parameters we measured. At this scale, Eastern Whip-poor-wills most frequently occupied areas lower in elevation and characterized by forested, herbaceous, and wetland cover types. In contrast, high elevation conifer forest communities had substantially fewer Eastern Whip-poor-wills. Detection rates were positively correlated with moon visibility and negatively correlated with noise. We used the results of our surveys to generate a regional model to predict distributions of Eastern Whip-poor-wills and that can be used as a framework for future management. Our results suggest that succession of agricultural fields and other clearings into forested habitats with dense understory may be a contributing factor to ongoing declines of Eastern Whip-poor-wills.

West Virginia↗

USGS2025

Methodology

Following the approach developed by Gregory and van Strien (2010), State of the Birds reports focus on composite summaries of population change for collections of species that share common primary habitat or taxonomic affinity. In this report, we provide composite indexes for habitat-obligate species as defined in earlier reports (Grassland, Aridland, Eastern Forest and Western Forest), for several taxonomic-based groups (Shorebirds, Waterbirds, Geese and Swans, Sea Ducks, and Dabbling/Diving Duck species), and for species on our Tipping Point list with adequate data. Lists of species included in each habitat-obligate group are presented as supplemental material at StateoftheBirds.org.

Report↗

USGS1970

Waterfowl in relation to land use and water levels on the Spring Run Area

Low water levels during critical phases of the breeding cycle appear to have caused population declines of waterfowl and other marsh birds on the Spring Run Game Management Area. Pair-counts indicated a decline from 70 pairs of waterfowl in 1965 to 2 pairs in 1968. Nest success of upland nesting blue-winged teal (Anas discors) averaged 33% and mallards (Anas platyrhyncos) averaged 23%. Blue-winged teal selected nest sites closer to water than did mallards (314 feet versus 424 feet). Teal nested in ungrazed bluegrass (Poa pratensis) in preference to alfalfa (Medicago sativa) hayland. Bromegrass (Bromus inermis) was readily used by teal and mallards when it became available for nesting. Nest success of species nesting overwater was considerably higher: Redheads (Aythya americana) were 55% successful and 93% of 75 coot (Fulica americana) nests hatched. A study of dummy-nests showed nest success significantly higher on ungrazed than on grazed bluegrass. Grazing did not significantly lower total mouse populations but did change species composition because deer mice (Peromyscus maniculatus) increased as other species declined with grazing.

Iowa State Journal of Science↗

USGS1991

Federal research on the conservation of migratory nongame birds in the United States

In the United States, the term 'nongame birds' applies to all bird species that are neither hunted nor legalIy endangered or threatened. Although ultimate responsibility for protection of migratory nongame birds lies with the federal government, research and management efforts by the key federal landholding agencies have historically emphasized species of economic importance, game birds and endangered species. In response to various legislative actions between the late 1960s and early 1980s, however, there has been a gradual escalation of research directed towards conservation of migratory nongame birds in these agencies. These studies have focused on two broad objectives (a) development of population sampling and census methods, and (b) identifying habitat requirements of species and species groups and the impacts of habitat changes on populations. The bulk of this research has been conducted by the U.S. Fish and Wildlife Service and the U.S. Forest Service. In this paper, the missions and research structures of these agencies are described briefly, and selected research highlights are discussed at length. Specific examples are development of the Breeding Bird Survey and teasing apart the relative contributions of forest fragmentation on breeding and wintering grounds to declines in populations of Neotropical migrants. Nongame bird research activities in other agencies are also summarized. The cumulative research conducted to date is evaluated in the context of developing a national management strategy to meet future migratory nongame bird conservation needs. Important shortcomings in present federal programmes continue to be insufficient folIow-through from research results to direct management action and lack of coordination among agencies with a vested interest in nongame bird conservation. Pending legislation and recent maturation of a comprehensive migratory nongame bird policy in the Fish and Wildlife Service are indications that significant improvements in these areas can be expected.

Book chapter↗

USGS2020

The effects of management practices on grassland birds—Prairie Falcon ( Falco mexicanus )

Keys to Prairie Falcon ( Falco mexicanus ) management include maintaining cliffs with suitable recesses for use as nest sites (that is, the substrate that supports the nest or the specific location of the nest on the landscape), protecting nest sites from human disturbance by designating buffer zones, and maintaining open landscapes and habitats that support populations of ground squirrels ( Urocitellus species) and small birds.

Professional Paper↗

USGS2004

Estimating the use of morphometric measurements from museum specimens for sex determination in Mountain Plovers (Charadrius montanus)

The Mountain Plover ( Charadrius montanus ) is a shorebird species endemic to the dry, terrestrial ecosystems of the Great Plains and southwestern United States. Breeding Bird Survey data suggest that Mountain Plover populations have declined by >60% in the last 30 years. A better understanding of the population dynamics of the Mountain Plover is important in determining future management goals for this species. However, this effort is hampered by the inability to determine the sex of Mountain Plovers accurately under field conditions. In an effort to develop a simple method for sexing plovers in the hand, we measured external morphometric characteristics from 190 museum specimens of adult Mountain Plovers in alternate (breeding) plumage. Logistic regression and discriminant function analyses were performed on 10 external morphometric measurements (lengths of unflattened wing chord, 10th primary, central rectrix, outer rectrix, total head length, exposed culmen, culmen, bill depth, bill width, and tarsus). The results of these analyses indicated that Mountain Plover sexes were similar for all measures except culmen length. However, further analysis determined that culmen length accurately predicted sex in less than two-thirds of the specimens, suggesting that this measure is a poor predictor of sex in Mountain Plovers. Structurally, Mountain Plovers appear to be nearly identical between the sexes, and other methods of sexing birds (e.g., plumage characteristics, behavioral observations, or molecular markers) should be further assessed for devising a simple method for sexing Mountain Plovers under field conditions.

Western North American Naturalist↗

USGS1981

Waterfowl and their wintering grounds in Mexico, 1937-64

The U.S. Fish and Wildlife Service has been interested in migratory birds, especially waterfowl, in Mexico for many years, An early period of cooperation in waterfowl administration was culminated in 1937 with the final ratification of the Convention Between the United States and the United Mexican States for the Protection of Migratory Birds and Game Mammals, usually referred to as the Migratory Bird Treat. Management of waterfowl on this continent is primarily carried out by hunting regulations. Current information on the status of each species must be obtained each year to serve as a basis for any needed modifications in the regulations. In the United States and Canada, wildlife biologists of the U.S. Fish and Wildlife Service and the Canadian Wildlife Service annually make the surveys to obtain this basic information. But the Government of Mexico has made no comparable surveys. Mexicans are not interested in hunting waterfowl to the extent that citizens of the United States and Canada are. As a consequence, Mexico's Department of Game emphasizes activities other than waterfowl management. Waterfowl, especially ducks, winter in or migrate through Mexico in large numbers, so it is obvious that and continental surveys of the winter population should include Mexico. Some general investigations of waterfowl distribution there were made in 1926 and earlier by E. A. Goldman. He was familiar with much of Mexico because he and E. W. Nelson studied mammals and biota there for many years. In the 1930's, because of the greater emphasis on waterfowl conservation and management, more detailed surveys were made of the continental breeding and wintering populations. One of these activities was designated as the midwinter, or January, inventory. In the early 1940's the senior author, who had been the Central Flyaway Biologist since 1937, recommended that the waterfowl wintering grounds in Mexico be included in the coverage of the midwinter waterfowl inventory. This was arranged in 1947, and the first aerial coverage, which only included coastal localities, was made in January-February of that year. The information obtained confirmed the value and advisability of including the Mexican wintering grounds in the annual survey; beginning in 1951 the wintering grounds in the Mexican highlands also were included. The surveys of Mexico were continued, except in 1957, through 1965; after 1965 they were greatly reduced. Ground reconnaissance and surveys had begun in Mexico with the preliminary work of Goldman in 1926, but quantitative studies were not started until 1937. The ground surveys continued at intervals in various parts of the Republic until 1960. Ground surveys are invaluable for such purposes as securing ecological information, specimens of birds and plants, and historical data about the areas from local residents, but the only satisfactory method of obtaining accurate quantitative information on waterfowl populations and their distribution is by airplane. Consequently, the major emphasis since 1947 has been on the annual aerial surveys. Ground studies were made much less frequently and were carried out mainly to obtain correlative information on the waterfowl foods available, the ecology of habitats, and for liaison with wildlife officials and biologists in Mexico. An important reason for the surveys of the waterfowl wintering grounds in Mexico was to determine their adequacy for the population of birds using them, and their potential to accommodate additional waterfowl if the wintering grounds in the United States became inadequate and larger flights entered Mexico. Other advantages included providing accurate information to hunters and other interested persons in the United States regarding the waterfowl shooting in Mexico, and determining the current status of these birds and their habitats in that country. Some of these findings were previously summarized by us (Saunders and Saunders 1949; Saunders 1964).

Resource Publication↗