| Pacific loon | |
|---|---|
 | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Gaviiformes |
| Family: | Gaviidae |
| Genus: | Gavia |
| Species: | G. pacifica |
| Binomial name | |
| Gavia pacifica (Lawrence, 1858) | |
 | |
| Range of the Pacific loon Breeding Non-breeding | |
ThePacific loon orPacific diver (Gavia pacifica), is a medium-sized member of theloon, or diver, family.
The Pacific loon, previously considered conspecific with the similarblack-throated loon, was classified as a separate species in 1985.[2][3] The genus nameGavia comes from theLatin for "sea mew", as used by ancient Roman naturalistPliny the Elder.[4] Thespecific epithetpacifica is Latin for thePacific Ocean, the term meaning "peaceful".[5]
The phylogeny of this species is debated, with the black-throated loon and the Pacific loon traditionally being consideredsister species, whereas a study usingmitochondrial andnuclear intron DNA supported placing the black-throated loon sister to aclade consisting of the Pacific loon and the two sister species that are thecommon loon and theyellow-billed loon. In the former phylogeny, the split between the Pacific loon and the black-throated loon is proposed to have happened about 6.5 million years ago.[6]
Breeding adults are like a smaller sleeker version of common loon. They measure 58–74 cm (23–29 in) in length, 110–128 cm (43–50 in) in wingspan and weigh 1–2.5 kg (2.2–5.5 lb).[7] They have a grey head, black throat, white underparts and chequered black-and-white mantle. The black throat has purple reflections. Non-breedingplumage is drabber with the chin and foreneck white.[8] Its bill is grey or whitish and dagger-shaped.
In all plumages, lack of a white flank patch distinguishes this species from the otherwise very similarblack-throated loon. The Pacific loon can be differentiated from thered-throated loon in winter by the latter's paler look, the fact that the red-throated loon has less of a contrast between both the crown and hindneck and the throat, and the bill that looks to be upturned.[8]
Like othergaviiformes, the Pacific loon's legs are located towards the back of its body making it difficult for it to walk on land. The leg placement helps the loons efficiently forage for food underwater. The physiological structure of the Pacific loon makes taking off from land practically impossible, and the loon requires 30–50 yards on the water to successfully attain flight.[9] This distance requirement fortakeoff limits the number of lakes the Pacific loon can realistically breed and forage on.
The Pacific loon most actively calls in the spring and summer and has a wide range of calls. When feeding, the Pacific loon may produce an "ark"-like vocalization, a sharp, short call. Additionally, the Pacific loon has a call similar to that of its relative thecommon loon, it is a loud, eerie, oo-loo-lee wail or yodel that can travel for miles and is typically heard during the loon's breeding season. The loons can also make short and harsh "kok-kok-kok-kok" calls along with a range of other smaller cackles, growls, barks, and clucking noises.[8][9]
The Pacific loon breeds ontundra lakes, and winters in the open ocean or other large bodies of water. It breeds primarily in northern Canada and eastern Siberia, and winters along the Pacific coast of North America.[10]
Unlike other loons/divers, this bird maymigrate in flocks. It winters atsea, mainly on thePacific coast, or on large lakes over a much wider range, includingChina,Japan,North Korea,South Korea, United States andMexico. It has occurred as a vagrant toGreenland,Hong Kong,Great Britain,Spain,Finland and Switzerland (Dec 2015).[11]
The Pacific loon constructs its nest on the ground near deep lakes. This nest is made out of piled-up vegetation.[12]
This loon lays aclutch of one to two light buff or green eggs with brown spots of various sizes. These eggs typically measure 76 by 47 millimetres (3.0 by 1.9 in). Although the eggs are laid a few days a part, they can usually be seen to hatch at intervals not more than a day. Incubation lasts 23 to 25 days.[12]
Socially monogamous Pacific loons have been found to have high territory retention rates (0.92) indicating that the loons are able to successfully defend their nesting lake from other loon pairs or individuals who may be trying to move in. Furthermore, males have a greater success at territory retention than females, but no evidence suggests that this difference is attributed to size but is rather due to fighting ability or familiarity with territory.[13]
Pacific loons prospecting for a new lake frequently visited lakes that were already occupied, this along with high retention rates of lakes indicates that the loon population in NorthernAlaska may be saturated. The Pacific loon has also been known to be veryaggressive, engaging ininterspecific killing of both hatch year and after hatch year individuals who intentionally or accidentally approach the loon's nesting area.[14]
A pair of Pacific loons will defend young as a parental unit in which one parent protects the nest orfledglings while the other parent aggressively attacks the perceived threat. If the threat is another animal on the water, the attacking loon will extend its head and neck in an aggressive manner and dive under the threat in an attempt to stab it with its beak as it resurfaces.[15][14] Pacific loons are so aggressive, they have even been observed displaying threatening body language towards passingairplanes in Alaska.[15]
Thisspecies, like all divers/loons, is a specialistfish-eater, catching its prey underwater. It also forages in groups, usually swimming under schools of fish and forcing them up towards the surface.[12] It does, although, generally feed closer to the shore than other loons.[8]
The Pacific loon population is currently increasing and is spread over a wide range of approximately 15,700,000 square kilometers.[16] Current efforts of conservation are focused around loon population monitoring and maintaining accurate counts of populations and breeding behaviors. A recent in depth study of the Pacific loon population in the Western AlaskanArctic found that the population of the birds there is actually ~1.5-2.0 times larger than previousaerial surveillance had indicated. The study indicated potential encroachment upon theNational Petroleum Reserve in Alaska (NPRA), one of the Pacific loons primarybreeding grounds, by natural gas and oil companies as a potential threat to Pacific loons.[17]
One harmfulenvironmental pollutant to the Pacific loon population is heavy metals like mercury, which can be observed in their habitat as a result of legacymining in the areas the loons migrate through and hunt in. It has been shown that elevated levels of mercury in the environment poses a significant health risk to avianpiscivores like the Pacific loon.[18] Mercury is up-taken by small fish which is a primary source of food in a loon's diet. When a loon eats the fish it will incorporate the mercury from the fish into its body, which can cause adverse health effects.
Additionally, it has been shown that nest visits from researchers and capture events can have a significant impact on thesurvival rates within Pacific loon nests. When investigators capture Pacific loons while they are breeding orincubating eggs regardless of how close they are to the nest at the time of capture, the survival rates of the eggs decrease.[13] This is most likely due to the fact that Pacific loons nest in a traditionally remote part of Western Alaska and are not typically accustomed to human interaction of any form. The lowered survival rate of the loon's offspring when a parent is captured or the nest is visited indicates that the population could face severe consequences from encroaching human contact.
Reports also exist of Pacific loons ingesting polluted plastic, a problem that is becoming an increasingly high concern among avians in Canada and across the globe. Luckily, the divingforaging behavior of loons keeps them at a relatively low risk of death from overconsumption of plastic, as most of the polluted debris exists floating on the surface of the water rather than in the depths.[19]
The following articles deal with separation of Pacific diver/Pacific loon from black-throated diver/Arctic loon:
