Meeting Abstract
94.1 Wednesday, Jan. 7 Is avian migration in the American Southwest timed to the bloom of columnar cacti? ENGEL, S.*; HYDE , T.; WOLF , B. O.; Univ. of New Mexico, Albuquerque sengel@unm.edu
During spring time in the Sonoran Desert, columnar cacti like saguaro produce an abundance of nectar- and pollen-rich flowers, the seasonal timing of which is very predictable and mainly dependent on spring temperature. Flowering thus occurs in a wave, starting out in Northern Mexico and moving north into Arizona. Since the geographic range of saguaro overlaps widely with the migration routes of many bird species we hypothesize that cactus nectar may be an important food source during spring migration, and that migration may actually be timed to follow the wave of cactus bloom. We took advantage of the fact that cactus nectar has an isotopic CAM value (δ13C=12.8 ‰ VPDB) which is very distinct from other (C3) resources available at this time of the year (δ13C=24.9 ‰ VPDB). We collected samples of breath and blood from 37 bird species (Warblers, Flycatchers, Finches, Orioles, and other) captured in Southern Arizona during migration from late April to end of June. This time period encompassed the local cactus bloom, starting early May and peaking in late May. Since carbon has very different turn-over rates in breath, plasma and red blood cells, we can determine the relative importance of cactus nectar as feeding resource for a time frame from very recently (breath) to several weeks ago (red blood cells). This allows us to model the temporal utilization of this short-lived but super-abundant food resource and to infer the degree to which migration is timed to columnar cactus bloom.
