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Research about North America

Source-linked reports with geographic coverage including North America.

At least 199 records · Page 11Linked to original sources
USGS1995

Amphibians

Amphibians are ecologically important in most freshwater and terrestrial habitats in the United States: they can be numerous, function as both predators and prey, and constitute great biomass. Amphibians have certain physiological (e.g., permeable skin) and ecological (e.g., complex life cycle) traits that could justify their use as bioindicators of environmental health. For example, local declines in adult amphibians may indicate losses of nearby wetlands. The aquatic breeding habits of many terrestrial species result in direct exposure of egg, larval, and adult stages to toxic pesticides, herbicides, acidification, and other human-induced stresses in both aquatic and terrestrial habitats. Reported declines of amphibian populations globally have drawn considerable attention (Bury et al. 1980; Bishop and Petit 1992; Richards et al. 1993; Blaustein 1994; Pechmann and Wilbur 1994). Approximately 230 species of amphibians, including about 140 salamanders and 90 anurans (frogs and toads) occur in the continental United States. Because of their functional importance in most ecosystems, declines of amphibians are of considerable conservation interest. If these declines are real, the number of listed or candidate species at federal, state, and local levels could increase significantly. Unfortunately, because much of the existing information on status and trends of amphibians is anecdotal, coordinated monitoring programs are greatly needed.

Book chapter↗
USGS1994

Shorebirds in western North America: Late 1800s to late 1900s

Only anecdotal information is available to assess whether populations of the 47 shorebird species that breed or winter west of the Rocky Mountains changed in size or distribution during the past century. Unregulated hunting from 1870 to 1927 reduced populations of several species, at least temporarily, and was a factor in bringing the Eskimo Curlew ( Numenius borealis ) close to extinction. Large scale transformation of native grasslands and wetlands for agriculture and other purposes resulted in population declines and nesting range contractions of several temperate-zone breeders. In general, upland species were affected more than wetland species, breeding ranges contracted westward, and alteration of breeding habitat was the factor most responsible for range contractions and population declines. A ranking system assessing shorebird susceptibility to habitat alteration also predicted temperate breeders to be among the most vulnerable species to environmental change. The few estimates for current population sizes of western North American shorebirds range from fewer than 50 Eskimo Curlews to a few million Western Sandpipers ( Calidris mauri ), the most abundant species. Concentrations of at least 1000 shorebirds occur on migration at over 120 western North American sites and of 100,000 to 1,000,000 shorebirds at 18 sites. Whether populations are limited by conditions on breeding, wintering or migration ranges is unknown for most species. Expansion of ongoing programs coupled with economical new census efforts could be useful for monitoring the majority of western North American shorebirds during the next century.

Studies in Avian Biology↗
USGS1994

Biology of North American tortoises

Chelonians have fascinated people for centuries and have been the object of biological studies for nearly as long. Perhaps the long life span and harmless demeanor of most species contribute to their wide appeal. they also represent a link to the distant past because their characteristic shell separated this line of ectotherms from all other reptiles and all other animals in the age of dinosaurs (Pough et al. 1989). However, the origins of chelonians remain a mystery.

Fish and Wildlife Research↗
USGS1993

Overwinter distribution of northern pintail populations in North America

Northern pintails ( Anas acuta ) exist as a single circumpolar breeding population but display weak fidelity to given breeding sites. If fidelity to wintering areas is strong, management on wintering grounds may allow local winter populations to increase. Thus, I delineated reference areas for wintering areas based on recovery data for pintails banded during the winter (Dec-Feb) in the United States. Fidelity to these reference areas varied with the strongest fidelity observed for pintails banded in areas along coastal areas or near large bodies of water such as western Washington-northwestern Oregon, central California, northwestern Utah, the Texas-Louisiana Gulf Coast, and the Greater Chesapeake Bay Region. My analysis suggests that pintails occurred in distinct wintering populations and that wintering ground affiliations to certain areas appear to be more stable population units than breeding ground affiliations. Consequently, winter banding programs may be useful in monitoring survival of specific wintering populations of concern.

North America↗
USGS1993

Survival of northern pintails banded during winter in North America, 1950-88

From 1950 through 1988, the continental breeding population of northern pintails ( Anas acuta ) varied from 2.0 million to 9.9 million. Because pintails have high fidelity to certain wintering grounds along coasts and large bodies of water, management on these wintering areas may increase population size if changes in winter survival rate are related to changes in population size. I used band-recovery data to estimate survival rates for winter-banded pintails and to test for sex-specific, temporal, and geographic variation in survival rates. Survival rate estimates varied between 0.632 and 0.806 for males, and 0.421 and 0.769 for females. Males had higher ( P < 0.0001) average annual survival rates than females. Limited geographic variation occurred in estimates of average annual survival rates for males, and no variation occurred for females. Males had lower average annual survival rates in the Imperial Valley than in central California ( P = 0.007) or in the Gulf Coast ( P = 0.092). Little annual variation was found within time periods. However, longer-term variation was found in survival rate estimates for males and females. Males had higher ( P = 0.054) average annual survival rates in the Pacific Flyway during 1959-61, a period of drought, breeding-population decline, and restrictive hunting regulations, than during 1950-58, a period with a higher breeding population and liberal regulations. The increase in wintering population size in the Pacific Flyway during the 1970's was associated with a higher average annual survival rate for females in the Pacific Flyway than during the 1950's. Results from the Pacific Flyway suggested that an interaction may exist between population size and the effect of harvest regulations on survival of males. Changes in harvest regulations appeared to have a greater effect at lower population levels.

North America↗
USGS1992

The zebra mussel (Dreissena polymorpha), a new pest in North America: reproductive mechanisms as possible targets of control strategies

The zebra mussel (Dreissena polymorpha) has spread rapidly in temperate fresh waters of North America since its introduction into the Great Lakes in 1985 or 1986. It attaches to hard substrates, forming layers, occluding water intakes, encrusting and killing native mussels, filtering algae in competition with other planktivores, and possibly interfering with fish spawning. It reproduces prolifically, suggesting that an approach to its control may be by controlling its reproduction. Previous literature suggests that spawning in bivalves is regulated by both environmental and internal chemical cues. A suggested sequence is that phytoplankton chemicals initially trigger spawning; chemicals associated with gametes provide a species-specific pheromonal positive feedback for spawning; and the response to environmental chemicals is mediated internally by serotonin (5-HT). The role of 5-HT in zebra mussels is under investigation. Both males and females can be induced to spawn by either injection or external application of 5-HT. The response can also be activated by 8-hydroxy-2-(di-n-propylamino)-tetralin, an agonist at 5-HT 1A receptors. HPLC analysis has detected 5-HT as the major biogenic amine in both male and female gonads. 5-HT immunocytochemistry demonstrates nerves containing serotonergic fibers innervating gonads of both males and females, with prominent varicosities surrounding the follicles in both sexes. A role of 5-HT in mediating spawning responses in zebra mussels is thus strongly supported. These studies have shown that reproductive behavior of zebra mussels can be modified by outside chemicals, a property that may be exploited for purposes of control.

Invertebrate Reproduction and Development↗
USGS1992

The oldest known Rocky Mountain bristlecone pines ( Pinus aristata Engelm.)

We have found 12 living Rocky Mountain bristlecone pines ( Pinus aristata ) more than 1600 yr old, including four that are more than 2100 yr old, on Black Mountain, near South Park, and on Almagre Mountain, in the southern Front Range, Colorado. A core from the oldest of these trees has an inner-ring date of 442 B.C. This tree is therefore at least 2435 yr old and exceeds the age of the oldest previously reported Rocky Mountain bristlecone pine by 846 yr. The ages of these trees show that Rocky Mountain bristlecone pines, under arid environmental conditions, achieve much older ages than have been previously reported. The ages also show that previously inferred trends in bristlecone pine ages, where maximum ages in the eastern range of Rocky Mountain bristlecone pines are much less than maximum ages in the western range of Great Basin bristlecone pines ( Pinus longaeva ), are less strong than previously supposed. Ancient Rocky Mountain bristlecone pines, such as those found in this study, have the potential to expand our knowledge of late Holocene climatic conditions in western North America.

Arctic and Alpine Research↗
USGS1992

Environmental influences on major waterfowl diseases

The decline of North American waterfowl resources since the 1960s is well-known to this audience and need not be detailed to establish that population numbers for several key waterfowl species are at or near their lowest levels since records have been kept. Loss of habitat is an accepted major cause for the decline of waterfowl numbers and the wildlife conservation community is responding with initiatives to prevent further loss of existing wetland acreage, restoration for degraded wetlands and creation of new wetlands. Numerous joint ventures focusing on key waterfowl habitat requirements are being developed under the North American Waterfowl Plan. The importance of habitat loss also is reflected in many of the presentations at this conference on wetland conservation, including one special session devoted solely to that topic. A basic premise of the focus on wetlands is that restoration of waterfowl populations is habitat dependent. This is a tenable thesis if other factors suppressing waterfowl numbers are dealt with and the habitat base being enhanced sustains waterfowl rather than contributes to their death. My presentation addresses disease as a factor suppressing waterfowl numbers and the relation of habitat quantity and quality with waterfowl disease.

Transactions of the North American Wildlife and Na↗
USGS1991

Mitochondrial and nuclear genetic relationships of deer ( Odocoileus spp.) in western North America

Odocoileus hemionus (mule deer and black-tailed deer) and Odocoileus virginanus (white-tailed deer) are sympatric in western North America and are characterized by distinct morphology, behavior, and allozyme allele frequencies. However, there is discordance among nuclear and mitochondrial genetic relationships, as mule deer ( O . h . hemionus ) and white-tailed deer have similar mitochondrial DNA (mtDNA) which is very different from that of black-tailed deer ( O . h . columbianus , O . h . sitkensis ). I expanded previous studies to clarify the genetic relationships of these groups by determining mtDNA haplotype and allozyme genotypes for 667 deer from several locations in northwestern North America. Different mtDNA haplotypes in mule deer, black-tailed deer, and white-tailed deer indicate that mitochondrial gene flow is restricted. Allozyme allele frequencies indicate that there is also restriction of nuclear gene flow between O . virginianus and O . hemionus , and to a lesser extent between mule deer and black-tailed deer. There is a low level of introgressive hybridization of mtDNA from mule deer and black-tailed deer into white-tailed deer populations and considerable interbreeding of mule deer and black-tailed deer in a contact zone. The discordance of mitochondrial and nuclear genomes is apparent only if mtDNA sequence divergences, and not haplotype frequencies, are considered.

Canadian Journal of Zoology↗
USGS1991

Introgression of coyote mitochondrial DNA into sympatric North American gray wolf populations

Mitochondrial DNA (mtDNA) genotypes of gray wolves and coyotes from localities throughout North America were determined using restriction fragment length polymorphisms. Of the 13 genotypes found among the wolves, 7 are clearly of coyote origin, indicating that genetic transfer of coyote mtDNA into wolf populations has occurred through hybridization. The transfer of mtDNA appears unidirectional from coyotes into wolves because no coyotes sampled have a wolf-derived mtDNA genotype. Wolves possessing coyote-derived genotypes are confined to a contiguous geographic region in Minnesota, Ontario, and Quebec, and the frequency of coyote-type mtDNA in these wolf populations is high (>50%). The ecological history of the hybrid zone suggests that hybridization is taking place in regions where coyotes have only recently become abundant following conversion of forests to farmlands. Dispersing male wolves unable to find conspecific mates may be pairing with female coyotes in deforested areas bordering wolf territories. Our results demonstrate that closely related species of mobile terrestrial vertebrates have the potential for extensive genetic exchange when ecological conditions change suddenly.

Evolution↗
USGS1989

Population trends of North American shorebirds based on the International Shorebird Survey

Shorebirds Charadrii are prime candidates for population decline because of their dependence on wetlands that are being lost at a rapid pace. Thirty-six of the 49 species of shorebirds that breed in North America spend most of the year in Latin America. Because populations of most species breed and winter at remote sites, it may be most feasible to monitor their numbers at migration stopovers. In this study, we used statistical trend analysis methods, developed for the North America Breeding Bird Survey, to analyze data on shorebird populations during southbound migration in the United States. Survey data were collected by volunteers in the International Shorebird Survey (ISS). The analyses indicate that whimbrels Numenius phaeopus , short-billed dowitchers Limnodromus griseus , and sanderlings Calidris alba have undergone statistically significant declines. Methodological concerns over both the ISS and the trend analysis procedures are discussed in detail and biological interpretations of the results are suggested.

Biological Conservation↗