Flightless Cormorants (Phalacrocorax harrisi), the only flightless members of their 27-member genus, are listed as vulnerable on the International Union for Conservation of Nature (IUCN) Red List. The world population of <1,000 breeding pairs is restricted to scattered small colonies along the coastlines of Isla Fernandina and Isla Isabela, Galápagos, Ecuador. No previous study has systematically examined daily activity patterns by these birds in relation to environmental variables. We made half-hourly behavior scan counts at a colony of Flightless Cormorants at Cabo Douglas, Isla Fernandina during the daylight hours of 7 consecutive days in May 2011. We used generalized linear models and multi-model inference to examine the response of colony occupancy and behaviors to hour of day, height of tide, temperature, humidity, wind speed, barometric pressure, solar elevation, and solar flux. We show that the behavior of Flightless Cormorants during our period of study was shaped primarily by time of day, wind speed, and solar flux; unlike many marine birds, they responded little to tide.