| Popis: |
Across North America, Sandhill Cranes (Antigone canadensis) use an array of migratory strategies, ranging from "jumping," or taking 1 or 2 flights from wintering grounds to a staging area, then on to the breeding grounds, to "hopping," or taking shorter flights among multiple (>3) staging areas between termini. We captured 16 adult and 2 juvenile Greater Sandhill Cranes (Antigone canadensis tabida) from the Lower Colorado River Valley population (LCRVP) and fitted them with platform transmitter terminals (PTTs) for GPS satellite telemetry. We used recorded locations and Brownian bridge movement models (BBMMs) to identify migration corridors and areas of migratory use (AMUs) during spring and fall migration (2014-2016). Eighty-nine percent of our sample (n = 16) of LCRVP Sandhill Cranes with PTTs flew direct paths between summer and winter termini. Starting in the Great Basin and moving into the Mojave Desert and then into the Sonoran Desert, the LCRVP aligned its migration with drainages, rivers, and reservoirs. Within those direct paths, we identified 18 unique and discrete AMUs along an ∼1000-km corridor and 3 within minor corridors taken by the other 2 cranes. We defined AMU as an area within a crane's 75% BBMM migration confidence contour where the crane had 2 or more subsequent time stamps (could be ≥3 hours) and did not travel >40 km from the first time stamp. The average migration duration was 23 days (spring, n = 3; fall, n = 2; cranes, n = 53). The fact that many individuals stopped several times after relatively short flights during both migration seasons suggests that the LCRVP generally uses a "hop" migration strategy. The use, often frequent and consecutive, of the 21 AMUs in this research reveals the potential importance of these migration areas to the LCRVP for its social, behavioral, and energetic requirements during migration. |
