Blue-footed Boobies are seabirds whose name comes from the Spanish "bobo", which means "stupid" and was probably inspired by the bird's clumsiness on land and apparently unwarranted bravery.
When breeding, Blue-footed Boobies roost on their ground nests; when day breaks, they leave the nests and fly, sometimes in cooperative groups, to sea in search for fish (Bennet and Owens 2001). They are excellent divers, and utilize two types of dives: V-shaped dives, in which the birds dive to a maximum depth and immediately return to the surface; and U-shaped dives, in which horizontal or zigzagging displacement occurs at the maximum dive depth (Garthe 2000). The most frequently used type of dive used is the V-shaped dive, but the U-shaped is used in deeper dives. Dive depth depends on the bird's: larger females can dive deeper than males. Their flying speed is about 39 km/h. Foraging trips can last a maximum of 13 hours, with an average of 86% of their foraging time spent in flight (Zavalaga et al. 2007).
Agonistic behavior occurs between siblings. There is a hatching asynchrony between eggs, so that one of the siblings is larger than the second In conditions such as a food shortages, when the larger chick may have an advantage in weight of 20%-25%, aggressive behavior towards the smaller sibling is triggered. This behavior consists of low-frequency pecking which causes the parents to feed the larger chick more frequently than the smaller one. Parents do not intervene in inter-sibling aggression. This behavior can result in the death of the smaller chick (Drummond et al. 1986).
Boobies thermoregulate attempt to lose heat at midday by postural adjustments, urohydrosis (defecating on the feet), and gular flutter, i.e., a rapid vibration of the hyoid muscles and bones in the throat to speed evaporative heat loss via the mouth (Townsend et al. 2002).
Blue-footed Boobies defend territories throughout the breeding season. The male and female jointly select a breeding site within a territory originally defended by the male (Stamps et al. 2002).
The mating system of the Blue-footed Booby is social monogamy. Pairs court frequently, with 38% of those copulations occurring in the fertile period. Males and females increase attendance at the nest site as laying approaches. They have frequent extra-pair copulations: 53% of paired females engage in them (Bennet and Owens 2001). Females, the larger sex, apparently control sexual access and copulate with extra males to achieve extra-pair fertilization. Males copulate with extra females, mostly outside their own mate's presumed fertile period, and they copulate increasingly with their social mate as laying approaches, probably assuring some paternity by mate guarding, involving attendance and courtship (Osorio-Beristain and Drummond 1998).
This species has a very complex courtship as part of which males and females exhibit their feet to their partner. Males land in the territory with spread feet held up and in front of their under parts producing a conspicuous contrast between the color of the foot-web and the white under parts (Torres and Velando 2003). This sexual advertising display is frequently preceded or followed by a parade consisting of an exaggerated foot-raising and flaunting of the webs upwards and outwards. Feet color is structurally and pigment based and it depends on the individual's capability to get food. It has been demonstrated that the chick's condition is related to the color of its father's feet so this trait is an honest signal of the male's condition (Velando et al. 2006) and his parental ability which makes it very important for females in mate choice (Velando et al. 2006). But feet color also works in reverse; it has been proven that females with duller color get less intra- and extra-pair courtship suggesting that males also use this trait to choose their mate (Torres and Velando 2005).
Social and interspecific behavior
The only study about interactions with other species was done on the Galapagos Islands. This study examined interactions between Blue-footed boobies and Nazca Boobies (Sula granti). At this site, Blue-footed boobies nest only in coastal areas when Nazca Boobies are absent, but when Nazca Boobies are present, Blue-footed Boobies use inland areas to establish their nests. This situation is apparently caused by attacks of non-breeding adult Nazca Boobies on Blue-footed Booby nestlings, injuring nestlings and ultimately preventing them from fledging (Townsend et al. 2002).
On the Galápagos Islands, the only predator of Blue-footed Boobies is the Galapagos Hawk (Buteo galapagoensis), the only diurnal bird of prey of the islands. This predator attacks nestling boobies when they attain 40% of their maximum weight and their parents begin to leave them unattended during parts of the day. The hawk mainly attacks the smaller and younger (second hatched) of the two nestlings. Nestlings are typically attended by at least one parent at night, offering protection from the only nocturnal predator, the Short-eared Owl (Asio flammeus). There have been no reports of nestlings killed by this owl (Anderson and Hodum 1993).