Text by Paula Dittrick, TMNCPC blog master, photos from GCBO web site and Eric Wolf, TMNCPC member.
The Gulf Coast Bird Observatory (GCBO) is studying the Loggerhead Shrike, which the GCBO web site says “epitomizes the dire conservation status of many grassland bird species” because its North American populations have declined nearly 80% within the last 50 years.
Consequently, the Loggerhead shrike is listed as endangered, threatened, or a species of concern across much of its range.
Cause(s) of the population decline remain uncertain, said Susan Heath, GCBO director of conservation research. It could stem from habitat loss. Shrikes prefer open country with scattered bushes while much such land has been turned into alfalfa and corn fields. Heath said pesticide use might be involved by affecting the shrikes’ food supply.
The Texas Gulf coastal prairie hosts both migrant and resident shrikes during the non-breeding season (November-February). Researchers are studying how migratory and resident populations coexist during the winter.
“Is winter habitat affecting migrant shrikes’ ability to reproduce the following spring,” Heath asked during a January presentation to the Texas Ornithological Society Virtual Winter 2021 Meeting.
Stable-hydrogen isotopes used along with genetic markers from feathers can identify migrant from resident shrikes. The ability to distinguish between migrant or resident helps researchers:
–better understand habitat partitioning.
–calculate the proportion of migrant to resident shrikes.
–determine the breeding origin of migrant shrikes wintering on the Gulf Coast.
Researchers use traps to catch shrikes for feather collection. Once a shrike is in hand, researchers also apply color bands to track the birds manually and Motus transmitters (nanotags) to track the birds with a Motus network. Tracking determines an individual bird’s winter habitat.
“Once these individuals are determined to be a migrant or a resident with the stable isotope-genetic analyses information, we can use the habitat affiliation data to provide valuable information on differences in habitat quality for migrant and resident shrikes,” GCBO said.
GCBO’s project partners are the Texas Midcoast National Wildlife Refuge Complex and the Cradle of Texas Master Naturalists. Project financing has come from the Gulf Coast Joint Venture, Texas Ornithological Society, Arthur A. Seeligson Jr. Conservation Fund, and the National Fish and Wildlife Foundation.