Lois Webster Fund Report – Mountain Plovers 2021

Lois Webster Fund Progress Report

Understanding the effects of trophic interactions on Mountain Plover brood habitat selection and survival – July 2021 Progress Report

Casey Weissburg
Department of Biology
Colorado State University – Pueblo

Mountain Plover Nestlings by Casey Weissburg

As a Species of Concern in the State of Colorado, the Mountain Plover has suffered historic population losses of over 60% since monitoring began in the 1960’s. Yet major knowledge gaps remain in our understanding of potential trophic interactions between the Mountain Plover and its predator and prey species. In order to understand how the greater community might affect this species and better inform management practices, this project seeks to investigate how Mountain Plover brood land use and chick survival is influenced by the density distributions of mammalian and avian predators, as well as by forage availability and habitat structure.

Breeding surveys first began at 4 study areas in El Paso and Pueblo counties on April 1st, 2021. Late snow caused multiple delays in breeding and unusually wet conditions resulted in three sites being dropped from the study as plovers abandoned all breeding attempts at those locations. Monitoring of the Mountain Plover in these low elevation counties continued only at Chico Basin Ranch. Breeding surveys and nest searching began at our high elevation site, James Mark Jones SWA (hereafter, South Park), in mid-May, in coordination with Allison Pierce and Dr. Michael Wunder of the Wunder Lab at UC Denver.

Nest searching efforts at Chico Basin Ranch resulted in 14 nests. Of these nests, 4 successfully hatched, with 8 lost to predation and 2 abandoned during intense storm events. Delays in the delivery of our radio transmitters allowed for only 3 broods to be tracked from hatching until fledging or death. One brood successfully fledged one chick, with another chick confirmed lost to predation; the other two broods were fully depredated or lost to unknown causes. The first brood to hatch was lost entirely after four days; fate could not be confirmed due to the lack of a transmitter and the adult was never resighted. The final brood at Chico Basin Ranch hatched on July 10th and was tracked until it went missing on July 23rd, at only two weeks of age; with no radio signal anywhere in the study area, it is likely the chick was carried far away by a predator. With this, the breeding season at our low elevation site came to a close. Post-breeding flocks have already begun to leave the site.

Of particular interest at Chico Basin Ranch is a potentially significant interaction between the plover broods and Burrowing Owls. While data analysis will take some time, our anecdotal observations in the field suggest that broods actively seek areas of the landscape where owl encounter rates were lower. The danger of the interaction with burrowing owls was further emphasized by the fact that owls were responsible for two of the three predations of tagged plover chicks.

Nest searching efforts at South Park, where the study area and population are both larger, netted 38 nests, fewer than is typical for this site. Despite extreme precipitation events, 20 of these known nests hatched, along with at least 12 unknown nests whose broods were later encountered. Of these 32 broods, 21 were radio tagged and monitored daily as at Chico, from hatching or first encounter until fledging or loss. Of these 21 tagged broods, 6 were depredated and 5 were lost either due to the tagged chick’s death or unconfirmed causes. As of July 30th, 4 tagged broods have successfully fledged at least one chick each, with 6 tagged broods still active.

In addition to daily monitoring of brood locations, surveys for predators, insects, and habitat structure were conducted at both sites during the peak brood-rearing period of each site, with mammalian predators surveyed via camera trapping, avian predators by point counts, arthropods with pitfall traps and grasshopper sweeps, and habitat structure by simple groundcover and shrub measurements, all at landscape-wide locations in a standardized grid that encompassed all available habitat in the study areas.

While labor-intensive, the goal of this project is ultimately to map the spatial distributions of predator encounter rates, prey availability, and habitat structure, in the hopes of better understanding what factors might influence how the Mountain Plover selects habitat for successful rearing of young. These surveys continue at South Park for another two weeks. Our youngest broods at South Park are estimated to fledge between August 26th and 29th and daily monitoring for these broods will continue until chicks have fledged or been lost.

In conclusion, this season has been a long and challenging but very successful first season for our study. Our research would not have been possible without the grants provided by the Lois Webster Fund and Colorado Field Ornithologists, the trail cameras graciously loaned by CPW, the cooperation and support of the Wunder Lab and the eager undergraduates of our own CBASE program at CSU – Pueblo. We are so grateful for all of the support and effort that went into this project. We hope to collect more data next year, but in the meantime, we intend to conduct preliminary data analyses this fall and look forward to sharing some insights in our end-of-year report.

Single Mountain Plover by Casey Weissburg