The term seabird is used for many families of birds in several orders that spend the majority of their lives at sea. Seabirds make up some, if not all, of the families in the following orders: Procellariiformes, Sphenisciformes, Pelecaniformes, and Charadriiformes. Many seabirds remain at sea for several consecutive years at a time, without ever seeing land. Breeding is the central purpose for seabirds to visit land. The breeding period (courtship, copulation, and chick-rearing) is usually extremely protracted in many seabirds and may last over a year in some of the larger albatrosses; this is in stark contrast with passerine birds. Seabirds nest in single or mixed-species colonies of varying densities, mainly on offshore islands devoid of terrestrial predators. However, seabirds exhibit many unusual breeding behaviors during all stages of the reproductive cycle that are not extensively reported outside of the primary scientific literature.
Courtship stage The courtship stage of breeding is when pair bonds are formed and occurs before copulation and occasionally continues through the copulatory and chick-rearing stages of the breeding phenology. The sequence and variety of courting behaviors vary widely among species, but they typically begin with territorial defense, followed by mate-attraction displays, and selection of a nest site. Seabirds are long-lived, socially monogamous, birds that usually mate for life. This makes selecting a mate extremely important with lifelong implications for the reproductive success of both individuals in the pair.
Mating dances
Seabirds are one of the only avian families that include ritualized dances in their courtship. These dances are complex and can include displays and vocalizations that vary greatly between families and orders. Albatrosses are well known for their intricate mating dances. All species of albatross have some form of ritualized dance, with many species displaying very similar forms. Albatrosses' complex visual and vocal dances are considered some of the most developed mating displays in any long-lived animal. Both members of the pair use these dances as a proxy for mate quality and it is believed to be a very important aspect of mate choice in this family. For black-footed (Phoebastria nigripes) and Laysan albatrosses (P. immutabilis) there are ten described parts to their mating dance which can be given in various sequences. Several parts include "billing" where one individual gently touches the others bill and "sky pointing" where the bird rises on the tips of its toes, stretches its neck and points its bill upward. In the wandering albatross (Diomedea exulans), sky pointing is accompanied with "sky calling" where the displaying individual spreads its wings, revealing his massive 12 foot wingspan while pointing and vocalizing skyward. The mating dance may last for several minutes. It has been noted that many albatross species dance upon reuniting with their partner every year; however, for waved albatross (P. irrorata), the dance is longer and more involved in new pairs, or in pairs that failed to breed the previous season. Boobies are another group of seabirds known for their mating displays. Brown (Sula leucogaster), red-footed (S. sula) and blue-footed boobies (S. nebouxii) have at least nine described parts to their mating display. Sky pointing in boobies is similar to albatrosses; in the brown booby, sky pointing is described as a display where the male throws his head backwards, stretches his neck out, and usually gives a whistling vocalization. Parading is a well-known display in boobies as well; in this display, one individual in the pair – usually the male – walks upright, with his tail erect, swaying in an exaggerated manner from side to side while taking small steps. In blue-footed and red-footed boobies, parading also includes lifting and flaunting their brightly colored feet at their prospective partner.
Frigatebirds are known for their unusual displays and breeding system. Unlike other seabirds, frigatebirds have a lek-breeding system where displaying males aggregate in groups of up to 30 individuals with prospecting females flying overhead. However, unlike classic leks, the pair then builds a nest on the male's display site. The male then participates fully in nest defense, incubation, and chick-rearing. The main display that male frigatebirds use to attract females is a "gular presentation" where the male inflates his bright red throat pouch, points his head upwards and opens his wings. It has been shown experimentally that there is no correlation between energy expended by males during courtship display and mate selection by females.
Courtship feeding Once the pair bond is formed, courtship feeding occurs in some species. Courtship feeding is when one member of the pair presents the other with food in a ritualized way. Often the male feeds the female, but in certain species where the sex roles are reversed, the female may feed the male. Several reasons proposed as to why courtship feeding occurs is: 1) to help strengthen the pair bond 2) to reduce aggression between males and females and 3) to provide additional nutrition to the females during the egg-laying stage. Courtship feeding is seen in many gull and tern species. In common terns (Sterna hirundo), courtship feeding begins right at the start of pair formation with male terns carrying a fish around the breeding colony, displaying it to prospective mates. The direct benefits hypothesis (where the female obtains some immediate benefit for copulating with the male, food in this case) may explain why courtship feeding has evolved; however, this theory has recently been disputed with the suggestion that the rate of courtship feeding is a way for females to determine the quality of their mate through the handicap principle.
Same-sex pairing
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