Environmental constraints on haul-out and foraging dynamics in Galapagos marine iguanas

Galápagos marine iguanas (Amblyrhynchus cristatus) forage in marine habitats but spend most of their time hauled out on land. As they move between desert-like terrestrial haul-out sites and temperate-like marine foraging habitats, these ectotherms experience sudden and dramatic temperature differences accommodated primarily through behavioral instead of physiological adaptations. One of the most important adaptive behaviors is the scheduling of foraging and haulout, the timing of which is modulated by thermal constraints and depends on environmental conditions. We connected haul-out data to differential equation models based on a suite of environmental factors to estimate environmental constraint functions for the timing of foraging and haulout during the non-reproductive season, 30 April–16 May 2011, on a sandy beach and a rocky outcrop at Cabo Douglas, Isla Fernandina. The timing of foraging and haulout was constrained by solar elevation, tide height, heat index, and relative humidity at the sandy site (R 2 = 0.77 to R 2 = 0.80) and solar elevation, tide height, THW index, and hour of day at the rocky site (R 2 = 0.57). We also constructed management models capable of long-range predictions of haulout based on solar elevation, tide height, and hour of day. These models accounted for 72% and 51% of the variability at the sandy and rocky sites, respectively.