Seabirds like the red-footed booby have to regulate body temperature. Although their habitats are fairly uniform around the oceans, the climate is different throughout the world. Here in the Galapagos it could get a bit warm around this season.
All birds lack sweat glands, and to prevent overheating they employ mechanisms like rapid panting, called "gular fluttering." Fluttering the gular skin aids them in the evaporation of internal moisture and in lowering blood pressure. So whenever you see birds doing this, is has to do with regulating temperature, nothing more.