MODELING COLONY-SITE DYNAMICS: A CASE STUDY OF GULL- BILLED TERNS (STERNA NILOTICA) IN COASTAL VIRGINIA

摘要: We developed a Markov process model for colony-site dynamics of Gull-billed Terns (Sterna nilotica). From 1993 through 1996, we monitored breeding numbers Gull- billed and their frequent colony associates, Common hirundo) Black Skimmers (Rynchops niger), at sites along 80 km the barrier island region coastal Virginia. also flooding events renesting. col- ony survival, extinction, recolonization potential over four-year pe- riod. then used data on annual site occupation by to estimate parameters tested differences between nesting substrates (barrier vs. shell- pile). Results revealed dynamic system but provided no evidence that were Markovian, i.e. probability was occupied in one year not influenced whether it had been previous year. Nor did colony-level reproductive success season seem affect occupancy. Site survival re- colonization rates similar, estimated overall being 0.59. Of 25 during period, 16 or two years only, only three all four years. Flooding renesting both habitat types The nests shellpiles argues more effective management; augmentation with shell sand increase ele- vations as little 20 cm could have reduced number sites. low colony- fidelity observed suggests an management approach would be provide large / shellpile use terns. Sites may still subsequent Received 2 September 1997, accepted 19 March 1998.