Population trends and connectivity of snowy plovers on the Southern Great Plains of Texas, New Mexico and Oklahoma

Abstract

According to surveys conducted in 2007-2009, breeding snowy plovers (Charadrius nivosus) at saline lakes in Texas experienced a ~75% population decline in the preceding decade. Negative population trends of interior snowy plovers on the Southern Great Plains (SGP) are generally attributed to high predation rates, declining groundwater, stochastic weather events and potentially to heavy metal contamination. The specific objectives of this research were to evaluate current population trends and detection probability of snowy plovers of three separate populations on the SGP and to monitor within-breeding season and migratory movements across the SGP and to wintering grounds on the Gulf coast.

To determine long-term trends of SGP of Texas snowy plovers, weekly summer surveys of saline lakes in Texas were performed in 2017/2018 to compare with survey data from the last two decades. Also, 20-year survey data from Bitter Lake National Wildlife Refuge (BLNWR) in New Mexico and data from annual surveys from 2013-2017 at Salt Plains National Wildlife Refuge (SPNWR) in Oklahoma were used to develop plover trend data for these two NWRs. Finally, to more precisely estimate detection probabilities and density estimates at Salt Plains NWR, weekly distance sampling surveys were performed in 2017/2018. To monitor movements of snowy plovers via the Motus Wildlife Tracking Network, an array of automated telemetry towers were installed at 6 study sites in the SGP. These towers were used to detect nanotag transmitters attached to adult breeding snowy plovers.

Snowy plovers have declined in the last 2 decades, 44% at 2 lakes in Texas (P < 0.001) and 63% at BLNWR (P < 0.001), whereas snowy plovers at SPNWR appear stable (P > 0.05), based on both refuge-level annual surveys and distance sampling protocol and analyses. Snowy plover detection probabilities were nearly perfect (~100%) at Salt Plains NWR, which supports earlier estimates of high detection rates of regional snowy plovers.

Within breeding season movements of snowy plovers during 2017 and 2018 suggest that Salt Plains NWR is not connected to Texas nor New Mexico populations. Furthermore, only 2 individuals moved from New Mexico to Texas, revealing these populations are weakly linked and that some degree of isolation exists. Relatively frequent movements of snowy plovers to Lake B in Texas may be indicative of higher-quality breeding and foraging habitat for regional snowy plovers due to the occurrence of consistent freshwater artesian springs. Overall, such potentially low population connectivity may warrant further investigation into the genetic underpinning of small, isolated and potentially threatened subpopulations. Also, the protection of habitat at Lake B may prove crucial in regional snowy plover conservation.

Snowy plovers are most likely nocturnal migrants, and fall migration departures from the SGP are positively correlated to longer photoperiods and low surface wind speeds. Also, although Salt Plains NWR snowy plovers were commonly detected on the Gulf coast of Texas to Florida, no winter-ground resighting or detection confirmed locales of snowy plovers captured and marked in Texas and New Mexico, although some resightings of Texas snowy plovers on the Texas coast have been reported in the past. Results from this research will prove crucial to long-term conservation and planning efforts relative to understanding regional persistence and dis-connectivity among breeding populations of snowy plovers in the Southern Great Plains. Further efforts should focus upon linking genetic data with movement data to more thoroughly evaluate regional connectivity and persistence probabilities.

This thesis won 1st Place in the Texas Tech University Outstanding Thesis and Dissertation Award, Biological Life Sciences, 2021.