Griffin, C.P., Morrow, M.E. & Silvy, N.J. 1997: Insects as a possible limiting factor for Attwater's prairie-chicken Tympanuchus cupido attwateri. - Wildl. Biol. 3: 288.
Declines in Attwater's prairie-chicken Tympanuchus cupido attwateri numbers have been linked to loss of habitat, but recently, numbers also have decreased dramatically in areas where habitat loss has not occurred. In this study, Attwater's prairie-chicken declines are linked to insect abundance by demonstrating that insect biomass availability is less than necessary to maintain chick growth. Data were collected on insect consumption by Attwater's prairie-chicken chicks at the Small Upland Research Facility at Texas A&M University during 1995 and 1996. Chicks housed in a controlled environment consumed an average of 16.2 g of grasshoppers daily. This value was applied to wild birds to examine required insect availability for chick growth over a four-week period. Insect availability data were obtained through studies within Attwater's prairie chicken habitat. Insect abundance in Attwater's habitats may have been impacted by invasion by cattle egrets Ardea ibis and fire ants. Increased numbers of insectivorous species and individuals have contributed to the loss of insects, which are the primary food source for juvenile prairie grouse. Declines up to 75% have been reported for overall arthropod numbers in fire ant infested areas, and cattle egrets are known to ingest as much as 149.8 g of insects/adult and chicks daily. Pesticide use from surrounding agricultural areas also may add to declines in insects as Attwater's habitat becomes more fragmented with increases in row crops. These chemicals, through drifting of spray into Attwater's habitat and their direct effects on insect recruitment from adjoining crop lands, may reduce insect abundance in Attwater's prairie-chicken habitat. The combined effects of cattle egrets, fire ants, and insecticides on insect abundance represent a possible reason for the recent declines in Attwater's prairie-chicken numbers.
Key words: Attwater's prairie-chicken, insects, population decline, Texas, Tympanuchus cupido attwateri
Clifton P. Griffin & Nova J. Silvy, Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, Texas 77843, USA
Michael E. Morrow, Attwater Prairie-chicken National Wildlife Refuge, P.O. Box 519, Eagle Lake, Texas 77434, USA