Seabird breeding behavior
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;[1][2] 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.
[3] 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.
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.
[12] In blue-footed and red-footed boobies, parading also includes lifting and flaunting their brightly colored feet at their prospective partner.
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.
[31][32][33] Also in the order Charadriiformes (family Chionidae), there has been one reported occurrence of a female-female pair in the black-faced sheathbill (Chionis minor), but eggs in the clutch proved to be inviable.
[35] The experience with a site gained through forming a female-female pair may greatly improve the chances of future successful breeding for the non-genetic parent, which explains why it might be worth the short-term cost of raising another bird’s offspring.
[35] In another member of this family, the Cory’s shearwater (Calonectris diomedea borealis), same-sex pairing was recently discovered for the first time in a burrow-nesting seabird.
[37] In 2010, when a southern royal albatross (D. epomophora) couple hatched a chick in New Zealand, it represented the first record of a successful same-sex pair in this species.
[38][37] In a landmark study by Young et al. (2008),[39] she reported over 30% of laysan albatrosses in a colony in Oahu, Hawaii were same sex pairs.
Additionally, an unsuccessful female-female pair of highly endangered of short-tailed albatrosses (P. albatrus) has been documented on Kure Atoll, Hawaii.
Moreover, all seabirds have obligate biparental care, so it would be evolutionarily costly for the male to spend months of effort raising a chick that is not his genetic offspring.
[52] Nazca boobies (Sula granti) have been well studied at breeding colonies in the Galapagos for decades and also show no evidence of EPCs or EPFs; also not a surprising result since they only have one surviving offspring per year.
[56] Similar results were seen in black-browed (Thalassarche melanophris) and grey-headed albatrosses (T. chrysostoma) nesting on South Georgia Island.
[58][59] In the Cory's shearwater population from Vila islet, Santa Maria island, Azores, strong competition for nesting cavities/burrows may explain the occurrence of EPCs and EPFs, with small males facing higher risks of cuckoldry than large ones[60] EPCs and EPFs have also been demonstrated to occur in other families of seabirds.
In contrast to the results found in genetic studies of dovekie, EPP has been shown in several species of alcid including common murre (Uria aalge) and razorbill (Alca torda), both of which raise only one chick per year.
[61][62][63] It has been shown that female razorbills can determine whether or not an EPC leads to an EPF and only accept extra-pair sperm when it gives them a fitness advantage over their current mate.
[65] Mating with related individuals is rare in naturally occurring populations of birds due to the production of lower quality offspring suffering from the genetic effects of inbreeding depression.
Siblicide, the death of an individual due to the actions of members of its own clutch, is seen in several avian orders including egrets and kingfishers, some raptors, and grackles.
If both eggs hatch, the elder chick will push its sibling out of the nest area, leaving it to die of thirst or cold.
[76] Research has shown that high hormone levels in Nazca booby chicks are responsible for inciting their murderous behavior.
Three main forms of courtship behaviour can be observed in most penguin species with the male initiating the displays to attract a female mate and to establish a nesting site.
[91] Ecstatic displays are the first of the tree behaviours observed during courtship in which the male penguin bows low and raises its beak with a trumpeting squawk with its flippers lifted in the air and may sometimes shake or sway their head.
This behaviour varies among species once again, with the most prominent difference being that of the emperor penguin whose two partners stand with head touching with bills facing down, and softly braying (honking).
This behaviour is believed to also strengthen the pair bond between the couple and is usually noted when one partner returns to the nest when foraging for food or other resources.
Upon arrival of the female mate, the cormorant performs a "wing flapping" behaviour in which the male assumes a horizontal stature, erects its tail with spread plumage, head drawn back with its neck touching its dorsal side and raises its beak with inflated gorge to the sky, and will often produce a cackling cry.
[97] Courtship behaviour takes place in groups at breeding ground sites and is initiated by the male who performs aerial displays near group nesting sites by flying in wide circles up to approximately 100 meters in the air, performing calls in sync with beats of their wings, and drooping their long tails and streamers down.
[98] This behaviour attracts many other nearby tropicbirds to perform aerial displays to form group sizes ranging from 6–12 individuals.
[97] Aerial displays when in a group are shown to most commonly occur during the morning, with numbers decreasing toward the afternoon as mates are selected or individuals give up[100][101]
