Section 6 - Environment Protection and Biodiversity Conservation (Wildlife Conservation Plan for Seabirds) Instrument 2022 - Wildlife Conservation Plan for Seabirds | Zoe
Environment Protection and Biodiversity Conservation (Wildlife Conservation Plan for Seabirds) Instrument 2022
6Wildlife Conservation Plan for Seabirds
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Seabirds' life histories are largely different from those of land birds. In general, they are K-selected, that is, population numbers fluctuate at or near the carrying capacity of the environment in which they inhabit. K-selected species generally have a longer lifespan (up to 60 years), delay breeding for longer (for up to 10 years) and invest more effort into fewer young (Robertson 1993; Schreiber and Burger 2002). Most seabird species will only have one clutch a year, unless they lose the first, and many species (like the procellariids and sulids), only one egg a year (Schreiber and Burger 2002; Brooke 2004).
Care of young is protracted, extending for as long as six months, among the longest for birds. For example, frigatebirds have long periods of parental care with each chick fledging after four to six months and continued parental investment for up to 14 months (Metz and Schreiber 2002). Due to the extended period of care, breeding occurs every two years rather than annually for some species. This life-history strategy has likely evolved both in response to the challenges of living at sea (collecting widely scattered prey items), the frequency of breeding failures due to unfavourable marine conditions, and the relative lack of predation compared to that of land-living birds (Schreiber and Burger 2002).
Because of the greater investment in raising the young and because foraging for food may occur far from the nest site, both parents participate in caring for the young, and pairs are typically at least seasonally monogamous. Many species, such as gulls, shearwaters and penguins, retain the same mate for several seasons, and many petrel species can mate for life (Brooke 2004). Albatrosses and procellariids, which can mate for life, take many years to form a pair bond before they breed (Pickering and Berrow 2001; Brooke 2004).
Breeding
Seabird breeding colonies are highly variable. Individual nesting sites can be widely spaced, as in an albatross colony, or densely packed as with a tern colony. In most seabird colonies, several different species will nest on the same site, often exhibiting some niche separation. Seabirds can nest in trees or shrubs (if any are available), on the ground (with or without nests), on cliffs, in burrows under the ground and in rocky crevices. Competition can be strong both within species and between species, with aggressive species such as Sooty Terns pushing less-dominant species out of the most desirable nesting spaces (Schreiber et al. 2002). The Great-winged Petrel (Pterodroma macroptera) nests during the winter to avoid competition with the more aggressive species like the Flesh-footed Shearwater (Ardenna carneipes) in south-west Western Australia. When the seasons overlap, Flesh-footed Shearwaters will share burrows with young Great-winged Petrels in order to use their burrows for summer nesting (Serventy et al. 1971).
Many seabirds show remarkable site fidelity, returning to the same burrow, nest or site for many years, and they will defend that site from rivals with great vigour (Schreiber and Burger 2002). This behaviour increases breeding success, provides a place for returning mates to reunite, and reduces the costs of prospecting for a new site (Bried et al. 2003). Young adults breeding for the first time usually return to their natal colony, and often nest close to where they hatched. This tendency, known as philopatry, is so strong that a study of Laysan Albatrosses (Phoebastria immutabilis) found that the average distance between hatching site and the site where a bird established its own territory was 22 m (Fisher 1976). For some species, once these sites are lost, there are limited options for these species to “find” alternative locations and habitat. Given the gaps in seabird ecology, loss of these sites may pose a risk to certain seabird populations.
Wildlife Conservation Plan for Seabirds 7
Colonies are usually situated on islands, cliffs or headlands, which land mammals have difficulty accessing (Moors and Atkinson 1984). This is thought to provide protection to seabirds, which are often very clumsy on land. Colonies of breeding seabirds will also take advantage of artificial structures, breakwaters and offshore platforms. Breeding in colonies often arises in types of birds that do not defend feeding territories; this may be a reason why it arises more frequently in seabirds (Schreiber and Burger 2002). There are other possible advantages: colonies may act as information centres, where seabirds returning to the sea to forage can find out where prey is by studying returning individuals of the same species. There are disadvantages to colonial life, particularly the spread of disease and ectoparasites. Colonies also attract the attention of predators, principally other birds, and many species attend their colonies nocturnally to avoid predation (Keitt et al. 2004).
Migration
Like many birds, seabirds often migrate after the breeding season. Of these, the migration taken by the Arctic Tern (Sterna paradisaea) is the farthest of any
bird, crossing the equator in order to spend the Austral summer in Antarctica
(Egevang et al. 2010; Fijim et al. 2013). Other species also undertake trans-equatorial trips, both from the north to the south, and from south to north. The Sooty Shearwater (Ardenna grisea) undertakes an annual migration cycle that rivals that of the Arctic Tern; birds that nest in New Zealand and Chile spend the northern summer feeding in the North Pacific Ocean off Japan, Alaska and California, an annual round trip of 64,000 km (Shaffer et al. 2006).
Other species migrate shorter distances away from the breeding sites, their distribution at sea determined by the availability of food. If oceanic conditions are unsuitable, seabirds will immigrate to more productive areas, sometimes permanently if the bird is young (Oro et al. 2004). After fledging, juvenile birds often disperse further than adults, and to different areas, so are commonly sighted far from a species' normal range. Some species, such as some of the storm petrels, diving petrels and cormorants, rarely disperse at all, staying near their breeding colonies year-round.
Biologically important areas for seabirds in Australia
Australian Marine Parks (Commonwealth reserves proclaimed under the EPBC Act in 2007 and 2013) are located in Commonwealth waters that start at the outer edge of state and territory waters, generally three nautical miles (approximately 5.5 kilometres) from the shore, and extend to the outer boundary of Australia’s Exclusive Economic Zone (EEZ), 200 nautical miles (approximately 370 kilometres) from the shore. These marine parks have been established for the protection and conservation of biodiversity and other natural, cultural and heritage values of the parks. They contain biologically important areas for a range of protected seabird species, and management of these parks can contribute to the protection of these species, or the ecological processes that support them.