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At least 73 records · Page 4Linked to original sources
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↗
USGS1975

The role of indigenous wild, semidomestic, and exotic birds in the epizootiology of velogenic viscerotropic Newcastle disease in southern California, 1972-1973

During an epornitic of velogenic viscerotropic Newcastle disease (VVND) in southern California, free-flying wild birds, captive and free-ranging semidomestic birds, and exotic birds were collected from the quarantine area to determine their role in the epizootiology of the disease. The VVND virus was isolated from 0.04% of 9,446 free-flying wild birds, 0.76% of 4,367 semidomestic birds, and 1.01% of 3,780 exotic birds examined. Three house sparrows and 1 crow directly associated with infected poultry flocks were the only free-flying wild birds from which VVND virus was isolated. Among semidomestic species, ducks, quail, chukars, pheasants, peafowl, pigeons, and doves were found to be infected. Psittacines, pittas, and toucans accounted for 92% of the VVND virus isolations from exotic birds. In addition, domestic Newcastle disease virus (NDV) was isolated from 0.29% of the free-flying wild birds, from 1.65% of the semidomestic birds, and from 0.19% of the exotic birds collected. Hemagglutination-inhibition against domestic NDV was demonstrated in 0.24% of 3,796 wild bird serums, 8.28% of 2,004 semidomestic bird serums, and 3.90% of 231 exotic bird serums tested.Although few free-flying wild birds were infected with VVND virus in this epornitic, the isolation of domestic NDV strains from free-flying wild ducks and mourning doves suggests the potential for transportation of NDV over long distances by migratory birds.

Journal of the American Veterinary Medical Associa↗
USGS2022

Highly pathogenic avian influenza is an emerging disease threat to wild birds in North America

Prior to the emergence of the A/goose/Guangdong/1/1996 (Gs/GD) H5N1 influenza A virus, the long-held and well-supported paradigm was that highly pathogenic avian influenza (HPAI) outbreaks were restricted to poultry, the result of cross-species transmission of precursor viruses from wild aquatic birds that subsequently gained pathogenicity in domestic birds. Therefore, management agencies typically adopted a prevention, control, and eradication strategy that included strict biosecurity for domestic bird production, isolation of infected and exposed flocks, and prompt depopulation. In most cases, this strategy has proved sufficient for eradicating HPAI. Since 2002, this paradigm has been challenged with many detections of viral descendants of the Gs/GD lineage among wild birds, most of which have been associated with sporadic mortality events. Since the emergence and evolution of the genetically distinct clade 2.3.4.4 Gs/GD lineage HPAI viruses in approximately 2010, there have been further increases in the occurrence of HPAI in wild birds and geographic spread through migratory bird movement. A prominent example is the introduction of clade 2.3.4.4 Gs/GD HPAI viruses from East Asia to North America via migratory birds in autumn 2014 that ultimately led to the largest outbreak of HPAI in the history of the United States. Given the apparent maintenance of Gs/GD lineage HPAI viruses in a global avian reservoir; bidirectional virus exchange between wild and domestic birds facilitating the continued adaptation of Gs/GD HPAI viruses in wild bird hosts; the current frequency of HPAI outbreaks in wild birds globally, and particularly in Eurasia where Gs/GD HPAI viruses may now be enzootic; and ongoing dispersal of AI viruses from East Asia to North America via migratory birds, HPAI now represents an emerging disease threat to North American wildlife. This recent paradigm shift implies that management of HPAI in domestic birds alone may no longer be sufficient to eradicate HPAI viruses from a given country or region. Rather, agencies managing wild birds and their habitats may consider the development or adoption of mitigation strategies to minimize introductions to poultry, to reduce negative impacts on wild bird populations, and to diminish adverse effects to stakeholders using wildlife resources. The main objective of this review is, therefore, to provide information that will assist wildlife managers in developing mitigation strategies or approaches for dealing with outbreaks of Gs/GD HPAI in wild birds in the form of preparedness, surveillance, research, communications, and targeted management actions. Resultant outbreak response plans and actions may represent meaningful steps of wildlife managers toward the use of collaborative and multi-jurisdictional One Health approaches when it comes to the detection, investigation, and mitigation of emerging viruses at the human-domestic animal-wildlife interface.

Journal of Wildlife Management↗
USGS2024

Bird habitat value and management priorities of the California Winter Rice Habitat Incentive Program

Flooding rice ( Oryza sativa ) agricultural fields during winter to facilitate rice straw decomposition has mitigated the loss of some of the natural wetlands in California’s Central Valley. We conducted bird surveys in 253 rice checks (2,158 ha) within 177 rice fields in the Sacramento Valley during the fall and winter of 2021-2022 and 2022-2023 to evaluate factors influencing bird use of winter-flooded, post-harvest rice fields enrolled in the California Winter Rice Habitat Incentive Program. We counted 143,932 birds from 57 species, including dabbling ducks (86.4%), geese (8.0%), shorebirds (0.9%), wading birds (0.7%), and other birds (4.0%). Extrapolating from the lowest densities observed in rice fields during the 70-day mandatory flooding period, we estimated that properties enrolled in this public-private partnership provided habitat for at least 271,312 birds day-1 (16,248 ha; 2021-2022) and 147,315 birds day-1 (8,448 ha; 2022-2023), totaling >10 million bird-use-days each winter. Water depth had the greatest influence on bird abundance and diversity. Relatively shallow water depths (≤13 cm) had greater abundance of shorebirds, wading birds, and geese, and higher diversity, whereas intermediate depths (~23 cm) resulted in the greatest dabbling duck abundance. Duck, goose, and wading bird abundances were greatest and species richness and family diversity were highest 8 days after the onset of flooding in rice fields (typically late October), followed by a decline in bird use until 65-87 days post flooding, after which bird use increased slightly. Bird abundance and species diversity were lowest in rice fields with the greatest hunting intensity (≥3 days week-1). We identified several habitat variables that could be managed and prioritized by landowner incentive programs to increase bird use of winter-flooded rice, including water depth, variation in emergent vegetation height, mudflat habitat availability, rice check shape, hunting intensity, and post-harvest treatment of residual rice straw.

California↗
USGS2001

Bird-landscape relations in the Chihuahuan Desert: Coping with uncertainties about predictive models

During the springs of 1995–1997, we studied birds and landscapes in the Chihuahuan Desert along part of the Texas–Mexico border. Our objectives were to assess bird–landscape relations and their interannual consistency and to identify ways to cope with associated uncertainties that undermine confidence in using such relations in conservation decision processes. Bird distributions were often significantly associated with landscape features, and many bird–landscape models were valid and useful for predictive purposes. Differences in early spring rainfall appeared to influence bird abundance, but there was no evidence that annual differences in bird abundance affected model consistency. Model consistency for richness (42%) was higher than mean model consistency for 26 focal species (mean 30%, range 0–67%), suggesting that relations involving individual species are, on average, more subject to factors that cause variation than are richness–landscape relations. Consistency of bird–landscape relations may be influenced by such factors as plant succession, exotic species invasion, bird species' tolerances for environmental variation, habitat occupancy patterns, and variation in food density or weather. The low model consistency that we observed for most species indicates the high variation in bird–landscape relations that managers and other decision makers may encounter. The uncertainty of interannual variation in bird–landscape relations can be reduced by using projections of bird distributions from different annual models to determine the likely range of temporal and spatial variation in a species' distribution. Stochastic simulation models can be used to incorporate the uncertainty of random environmental variation into predictions of bird distributions based on bird–landscape relations and to provide probabilistic projections with which managers can weigh the costs and benefits of various decisions. Uncertainty about the true structure of bird–landscape relations (structural uncertainty) can be reduced by ensuring that models meet important statistical assumptions, designing studies with sufficient statistical power, validating the predictive ability of models, and improving model accuracy through continued field sampling and model fitting. Uncertainty associated with sampling variation (partial observability) can be reduced by ensuring that sample sizes are large enough to provide precise estimates of both bird and landscape parameters. By decreasing the uncertainty due to partial observability, managers will improve their ability to reduce structural uncertainty.

Chihuahua, Coahuila, Nuevo León, Tamaulipas, Texas↗
USGS2022

Host plant associations of Lepidoptera and implications for forest bird management at Hakalau Forest National Wildlife Refuge

Forests dominated or co-dominated by ‘ōhi‘a ( Metrosideros polymorpha ) are critical to most Hawaiian forest birds, but fungal diseases causing Rapid ‘Ōhi‘a Death (ROD) threaten ‘ōhi‘a-based food webs that support native bird communities on Hawai‘i Island. Caterpillars are the most frequently consumed arthropod prey of native birds and their young and are especially frequent in the diets of one threatened (T) and three endangered (E) species (“listed” species) at Hakalau Forest National Wildlife Refuge (Hakalau): ‘akiapōlā‘au ( Hemignathus wilsoni , E), ‘alawī (Hawai‘i creeper; Loxops mana , E), Hawai‘i ‘ākepa ( L. coccineus , E), and ‘i‘iwi ( Drepanis coccinea , T). Hakalau harbors the largest and most stable populations of listed forest birds in Hawai‘i, presumably due to the availability of food resources and the extent of suitable, managed habitat above the range of mosquito-borne avian malaria. Because a previous study indicated that only a few caterpillar species were important in the diets of listed birds at Hakalau, we investigated the distribution of caterpillars on common host plants available to foraging birds. Eleven native plant species hosted two or more taxa identified to genus or species, with at least seven from ‘ōhi‘a, six from koa ( Acacia koa ), and five from ‘ākala ( Rubus hawaiensis ). We identified 16 taxa to genus or species from 9 families, assigning 11 to species. Leaves, which were the focus of our sampling effort, were the substrate used by 20 caterpillar taxa, and dead wood or bark was used by 7 taxa. In a previous study, we classified 19 morphotypes of caterpillar mandibles in the diets of native and alien birds at Hakalau, and in the present study we dissected mandibles from caterpillars that likely matched 10 of those morphotypes. These 10 morphotypes potentially represented >95% of caterpillar prey found in the earlier diet study and were collected from 11 host plant species, with ‘ōhi‘a hosting 8 morphotypes, 4 of which were exclusive to ‘ōhi‘a. The most widely hosted morphotype was found on all 11 plant species that we sampled, including ‘ōhi‘a, but the other 9 morphotypes were found on 1–7 hosts. As shown by the previous diet study, each of the listed bird species consumed caterpillar prey consisting mostly of combinations of two morphotypes drawn from a pool of only five, indicating a high degree of specialization. In the present study, we collected three of the five key morphotypes only on ‘ōhi‘a, highlighting the importance of this tree to listed bird species. Because ‘ōhi‘a forests in Hakalau remain vulnerable to ROD, measures to mitigate the impacts of reduced ‘ōhi‘a cover are important to consider from the perspective of forest bird food webs and diet. Ongoing reforestation of former pasturelands with koa and common understory species should provide alternative caterpillar prey for forest birds. Our results and information from the literature indicate that koa supports, to varying degrees, nearly all forest birds at Hakalau, while ‘ākala, ‘ōhelo ( Vaccinium calycinum ), kōlea ( Myrsine lessertiana ), ‘ōlapa ( Cheirodendron trigynum ), pūkiawe ( Leptecophylla tameiameiae ), and māmaki ( Pipturus albidus ) could benefit bird populations by increasing prey availability and structural complexity in koa-dominated stands. Foraging studies and additional research to identify species and host plant associations of important forest bird prey, including caterpillars and other arthropods, can help managers evaluate the complex interactions between native forest birds and their food webs and habitats.

Hawaii↗