Geology topics

Vijay P. Patil

Publications and source records attributed to Vijay P. Patil.

23 records · Page 2Linked to original sources

USGS2019

Visualizing populations of North American sea ducks: Maps to guide research and management planning

North American sea ducks generally breed in mid- to northern-latitude regions and nearly all rely upon marine habitats for much of their annual cycle. Most sea duck species remained poorly studied until the 1990s when declines were noted in several species and populations. Subsequent research, much of which was funded by the Sea Duck Joint Venture, began in the late 1990s with an emphasis on defining use areas throughout the annual cycle, migration patterns, and determining if there were distinct populations, within species, across North America. These studies relied largely upon satellite telemetry information to identify winter, breeding, and molting areas of sea ducks. New information from band recovery and genetic markers was added, contributing to hypotheses and initial conclusions about population delineation. Information on population units across North America is critical for identifying appropriate scales for evaluating population status and trends through annual monitoring surveys, harvest assessments, habitat protection and measuring effectiveness of management applications. Previous descriptions of population segments were for single species or smaller groups of similar species. Here, we summarize current knowledge on the general distribution and population segments of 13 species of sea ducks in North America by comparing range maps to long-term band recovery, genetic, and satellite telemetry data to inform population delineation assessments and future research. These comparisons show a high degree of consistency in population patterns for most species across the independent data types. These maps provide a foundation for developing new hypothesis-driven research to address remaining knowledge gaps and questions about population differentiation, annual cycle distribution, habitat use, and harvest assessment.

North America↗

USGS2019

Survival of Bristle-thighed Curlews equipped with externally mounted transmitters

Telemetry devices are widely used in avian research, but the degree to which the deployment of such devices affects the survival of study subjects is often not addressed. It is generally assumed that such effects are less pronounced in large-bodied species that conduct relatively short migrations and carry relatively light telemetry devices. We studied Bristle-thighed Curlews Numenius tahitiensis over the period 2012–2017 at a nonbreeding site on the island of Oahu, Hawaii. We used leg-loop harnesses to equip 11 curlews with externally mounted, solar-powered satellite transmitters that constituted ca. 3% of their body mass, and compared the annual survival of these birds to 37 curlews marked only with uniquely engraved leg flags. Despite the species’ large size and the small mass of the transmitters, we documented potential negative effects of externally mounted transmitters on the survival of Bristle-thighed Curlews. We also documented apparent effects of age and sex on the survival of curlews, underscoring the difficulty of disentangling the effects of research techniques on study subjects. Understanding and publicizing the potential effects of research itself on wildlife are crucial steps in the process of refining technical applications and improving the welfare of study animals. We urge researchers to critically assess and report the effects of similar research techniques to minimize deleterious effects in future studies.

Wader Study↗

USGS2019

Factors promoting the recolonization of Oahu, Hawaii, by Bristle-thighed Curlews

Suitable habitat for Arctic-breeding migratory shorebirds is decreasing at their traditional wintering islands and atolls in the Central Pacific Flyway (i.e., Oceania) due to habitat degradation, reclamation, and sea-level rise. To maintain the size and resiliency of their populations, migratory shorebirds will need to expand their winter ranges by either colonizing new sites or recolonizing old sites from which they were extirpated. Bristle-thighed Curlews (Numenius tahitiensis) are long-distance migratory shorebirds that breed only in Alaska and winter across a vast region of the Central Pacific, typically on remote, unpopulated islands and atolls. Historically, Bristle-thighed Curlews were considered uncommon transients on the main Hawaiian Islands, but in the mid-1990s, curlews became regular visitors to Oahu and subsequently began wintering at the James Campbell National Wildlife Refuge on Oahu Island in Hawaii. Curlew numbers at this site grew steadily from <5 birds in the mid-1990s to an estimated 126 winter residents (95%CI 108–147) in 2013–2014. Timing of the recolonization event coincided with the establishment of a fenced pond complex that was managed for endangered waterbirds by maintaining areas of shallow water and low vegetation. High rates of apparent annual survival exhibited by adults and subadults (0.86–0.95) confirmed the suitability of the Refuge to curlews. Our results suggest that curlews in Oceania can naturally recolonize wintering islands, a trait that may be key to the survival of this species of conservation concern in an era of rising sea levels.

Hawaii↗

USGS2018

Consequences of gas flux model choice on the interpretation of metabolic balance across 15 lakes

Ecosystem metabolism and the contribution of carbon dioxide from lakes to the atmosphere can be estimated from free-water gas measurements through the use of mass balance models, which rely on a gas transfer coefficient ( k ) to model gas exchange with the atmosphere. Theoretical and empirically based models of k range in complexity from wind-driven power functions to complex surface renewal models; however, model choice is rarely considered in most studies of lake metabolism. This study used high-frequency data from 15 lakes provided by the Global Lake Ecological Observatory Network (GLEON) to study how model choice of k influenced estimates of lake metabolism and gas exchange with the atmosphere. We tested 6 models of k on lakes chosen to span broad gradients in surface area and trophic states; a metabolism model was then fit to all 6 outputs of k data. We found that hourly values for k were substantially different between models and, at an annual scale, resulted in significantly different estimates of lake metabolism and gas exchange with the atmosphere.

Inland Waters↗

USGS2017

Normalized difference vegetation index as an estimator for abundance and quality of avian herbivore forage in arctic Alaska

Tools that can monitor biomass and nutritional quality of forage plants are needed to understand how arctic herbivores may respond to the rapidly changing environment at high latitudes. The Normalized Difference Vegetation Index (NDVI) has been widely used to assess changes in abundance and distribution of terrestrial vegetative communities. However, the efficacy of NDVI to measure seasonal changes in biomass and nutritional quality of forage plants in the Arctic remains largely un-evaluated at landscape and fine-scale levels. We modeled the relationships between NDVI and seasonal changes in aboveground biomass and nitrogen concentration in halophytic graminoids, a key food source for arctic-nesting geese. The model was calibrated based on data collected at one site and validated using data from another site. Effects of spatial scale on model accuracy were determined by comparing model predictions between NDVI derived from moderate resolution (250 × 250 m pixels) satellite data and high resolution (20 cm diameter area) handheld spectrometer data. NDVI derived from the handheld spectrometer was a superior estimator ( R 2 ≥ 0.67) of seasonal changes in aboveground biomass compared to satellite-derived NDVI ( R 2 ≤ 0.40). The addition of temperature and precipitation variables to the model for biomass improved fit, but provided minor gains in predictive power beyond that of the NDVI-only model. This model, however, was only a moderately accurate estimator of biomass in an ecologically-similar halophytic graminoid wetland located 100 km away, indicating the necessity for site-specific validation. In contrast to assessments of biomass, satellite-derived NDVI was a better estimator for the timing of peak percent of nitrogen than NDVI derived from the handheld spectrometer. We confirmed that the date when NDVI reached 50% of its seasonal maximum was a reasonable approximation of the period of peak spring vegetative green-up and peak percent nitrogen. This study demonstrates the importance of matching the scale of NDVI measurements to the vegetation properties of biomass and nitrogen phenology.

Alaska↗