Snowy Plover population and breeding ecology in Saline lakes of the southern high plains of Texas

Snowy Plovers (Charadrius alerandrinus) have experienced declines throughout their range in the United States and are currently listed as threatened by the U.S. Fish and Wildlife Service along the Pacific Coast and as endangered, threatened, or of special concern in several states. The objectives for this research were to 1) estimate nest success and evaluate factors influencing nest success, 2) determine nest site selection patterns, 3) evaluate factors influencing incubation temperatures, 4) document offspring sex ratios and evaluate factors influencing sex ratio adjustment, 5) estimate apparent survival rates, and 6) document long-term changes in populations and evaluate factors influencing regional surveys counts of Snowy Plovers nesting on saline lakes within the SHP of Texas.;Overall, 215 nests were monitored from three saline lakes in 2008--2009, with Mayfield estimates of nest success ranging from 7--33% (mean = 22%) with leading causes of failure being predation (40%) and weather (36%). These results suggest that if nesting Snowy Plovers continue to experience increased predation rates, decreased hydrological integrity, and habitat alterations, populations will continue to decline throughout this region.;Habitat variables were collected at 180 nests in 2008--2009. Snowy Plover nests were best classified by pebble substrate, close to an object, and with more rocks, pebbles, and objects surrounding nests (i.e., 707-cm² plot) than random sites. Areas of high use within saline lakes generally were located in areas with pebble substrate and on manmade or natural islands, berms, and peninsulas. These results provide some guidance for habitat conservation and management strategies within this region.;Incubation temperatures from 104 Snowy Plover nests located on saline lakes within the SHP of Texas were examined in relation to 1) ambient substrate temperatures, 2) annual, temporal, and spatial variation, 3) nest site selection, 4) nest success, and 5) parental quality. Nest temperatures ranged from 12.7--47.2°C and varied between years and lakes. Within this region, Snowy Plovers may be able to alleviate some heat stress by performing adaptive behaviors, selecting pebble substrates, and initiating nests earlier in the season.;Sex ratios and sex allocation theory were examined for 245 chicks from 118 clutches during 1999--2000 and 2008--2009. Offspring sex ratios did not differ from parity, although were slightly male biased in the majority of years. Male offspring were more costly to produce than females, with the probability of producing a male offspring having a bimodal distribution with more males produced earlier and later in the season as compared to the middle of the season.;Return rates of adult Snowy Plovers were higher in 2000, with 77% of adults banded in 1999 observed in 2000, than 2009--2010, with only 58% of adults observed ≥ 1 year following capture. Current estimates of adult and juvenile apparent survival rates indicate that 5.8 hatchlings per adult per year are needed to maintain the current population without immigration; however, this is not physiologically possible during the short nesting season. Therefore, conservation efforts must focus upon increasing adult and juvenile survival on both breeding and wintering grounds.;From 1998--2010, 184 surveys were conducted with mean counts of adult Snowy Plovers declining by 55% over the last decade. Nest success and apparent survival are likely important factors for these declines, as mean nest success has declined by 31% from 1999--2009, and adult and juvenile apparent survival have declined by 25% and 60%, respectively. In order to properly monitor local populations and assess apparent population declines, understanding factors influencing regional survey counts can be important. In the SHP of Texas, surface water availability and time during the nesting season were the most important factors influencing the number of Snowy Plovers observed during surveys. Therefore, population estimates may vary considerably if surveys are not standardized to account for changes in these factors. (Abstract shortened by UMI.)...