We’re away, home again in September

Gerald McCormack, Natural Heritage Trust
First published (14 April 2021), short version CI News (14 April 2021)

Plover in breeding plumage ready for April departure.

The Pacific Golden Plover, or Tōrea, is our most common Alaskan migrant. It is conspicuous on larger grassy areas during the summer and most are now in their dramatic breeding plumage and ready to depart.

Cook Islands Tōrea

A new arrival fighting to regain its territory.

During our summer, the dull brown Tōrea or Pacific Golden Plovers (Pluvialis fulva) are common and widely spaced on grassy areas. They are very territorial and act aggressively towards any intruding plover. Each year they typically return to the same non-breeding territory, and should an earlier arrival have moved in, a serious dispute ensues, which is usually won by the original owner.

Plovers typically stand motionless in an upright posture on one leg and intermittently jog a few paces before standing still again. They are watching for small invertebrates in the grass which they grab with their beaks and immediately swallow.

When disturbed they take flight often giving their “tuuu-ree…..tuuu-ree” alarm call, which is the basis of their local names Tōrea (Rarotonga, Mangaia, Aitutaki, Manihiki, Rakahanga and Penrhyn), Toretōrea (Ātiu, Ma‘uke and Miti‘āro) and Tuli (Pukapuka and Nassau). Elsewhere in Eastern Polynesia they are known as Tōrea or a cognate: Tōrea in the Societies and Tuamotu, To‘ea in the Marquesas with their missing “r”, and Kōlea in Hawai‘i with their “k” for “t” and “l” for “r”.

Take care with Aotearoa Māori because they transferred Tōrea to two species of oystercatcher and then, not seeing any Wandering Tattlers, they applied its tropical Polynesian name Kuriri to their Golden Plover.

In Western Polynesia the plover is Tuli on Samoa, Tuvalu and Tokelau – as it is on Pukapuka, while Tonga and Niue are unusual in using the name Kiu. The Samoan and Tongan names also include the Wandering Tattler.

The Pacific Golden Plovers breed in Alaska during the northern Summer when food is abundant and temperatures are mild (7-14°C). After breeding, during the Fall or Autumn they migrate south to the tropical islands of the Pacific. The adults leave when as soon as their young can fend for themselves, and the young migrate alone a few weeks later. Americans describe this southward migration as the Fall migration to the plover’s wintering grounds, while we recognise them as our Summer, southern Summer, visitors.

The Trust studied the Tōrea on Rarotonga Airport 1994-1997 and concluded they left in large groups during the first two weeks of April and most returned in September-October. In those days there were about 130 birds within the airport in the late afternoon, consisting of the permanent residents of the grassed areas and the early arrivals from elsewhere on the island to take refuge on the runway to avoid nocturnal predators. Recent reports indicate a serious reduction in plover numbers on the airport and reductions have also been reported from various overseas locations.

Niue Kiu

Kinsky & Yaldwyn((Kinsky & Yaldwin (1981) The bird fauna of Niue Island, with special notes on the White-tailed Tropicbird and the Golden Plover. Natl. Mus. N.Z. Misc. Ser. 2)) studied plovers or Kiu on Niue in August-September 1972 and based on their fat reserves they concluded that most plovers were capable of flying non-stop the 8,500km from southwest Alaska to Niue. Plovers are unable to rest on the ocean, although there was some evidence from elsewhere indicating that some rest a few hours on islands along the route.

The adults started arriving at the beginning of September; juveniles arrived separately after the adults and they did not undertake their first breeding migration until they were in their second year.

Oahu Kōlea

Dole, in his 1879 “Birds of the Hawaiian Islands” was the first to establish that Kōlea depart Oahu in April-May and return late July-August.

Pacific Golden Plover migration routes reported to 2021.

A hundred years later, in 1996 Oscar (Wally) Johnson and his team put tiny radio transmitters on 20 Kōlea on Oahu and they managed to find three in southwest Alaska, and 19 returned to the same territories on Oahu. While this proved that Oahu plovers definitely flew to Alaska and back it did not provide any details of their route and stopovers.((Johnson et al. (1997) Migration by Radio-tagged Pacific Golden Plovers from Hawaii to Alaska, and their Subsequent Survival. The Yuk 114(3):521-524.))

The next technology breakthrough was with tiny geolocators which when recovered from birds provided details of their past locations. During 2009 and 2010 Johnson and his team obtained data on 19 northward tracks, 20 nesting locations and 18 southward tracks.((Johnson et al. (2011) Tracking the migrations of Pacific Golden-Plovers (Pluvialis fulva) between Hawaii and Alaska: New insight on flight performance, breeding ground destinations, and nesting from birds carrying light level geolocators. Wader Study group Bull. 118(1):26-31))

The Kōlea had left Oahu in the second half of April (18^th April – 4^th May) and most flew non-stop to the mainland of southwest Alaska.  Eighteen departed the breeding grounds from early July to mid-August (3^rd July – 24^th August), with nine of the 18 stopping on the Alaskan Peninsula for one to 40 days. From the Peninsula all birds flew non-stop 4,000km in four days back to their territories on Oahu arriving 8-27 August. The birds averaged about 60km/h. See map.

Two birds were of special interest because they overshot Oahu by about 500km and backtracked to the island. This showed they were not just following a compass bearing southward but were detecting latitude as well. Plovers use a GPS!

Tutuila Tuli

In early 2007, thirty plovers on Tutuila (American Samoa) were fitted with radio transmitters and most left the island in the second week of April. Although only one was detected in Alaska, 25 returned in August-October to occupy their original territories in Samoa.

Johnson and his team concluded that “it seems likely that plovers wintering in American Samoa are linked to Alaska via a mid-Pacific Flyway”.((Johnson et al. (2008) Pacific Golden-Plovers Pluvialis fulva in American Samoa: Spring migration, fall return of marked birds, and other observations. Wader Group Bull. 115(1):20-23.)) In other words, the Samoan plovers migrate directly north to Alaska and after breeding, south to Samoa.

However, geolocators on 19 birds in March 2010 showed an incredibly different story when 9 were recaptured on Tutuila in Aug-Sept.

The logger data showed the bird flew from American Samoa to central Japan a distance of 7,500km in an average of six days, averaging 60kph. They spent an average of 22 days (2-33) mainly feeding around the rice fields. They then flew 5000km to Alaska during an average of 3.5 days at about 73kph.  After breeding in Alaska, they flew 8,500km directly southward to Samoa taking about seven (5.0-7.5) averaging 64kph. See map.

Some additional central and south Pacific information was obtained from geolocators on some male birds in Alaska. The most interesting bird for us in the Cook Islands was the bird that went to Kiritimati in the Line Islands, northeast of Penrhyn. It flew 7,500km to Japan rather than reversing its southward flight to fly 6,000km to Alaska. Apparently, instinct overrides the shortest route provided by the plover’s GPS!

French Polynesia Tōrea

It has been commonly accepted that in ancient times Marquesans found Hawai‘i by observing the migration of the Tōrea, which depart in conspicuous groups. Did those plovers lead the Marquesans to Hawai‘i by flying north over Hawai‘i to Alaska?

In 2017 and 2018 the Johnson team put satellite trackers on twenty Tōrea on Mo‘orea in the Society Islands.((Johnson et al. (2020) Tracking the migration of Pacific Golden-Plovers from nonbreeding grounds at Moorea, French Polynesia, using Pinpoint GPS-Argos tags. Wader Group 127(1):1-7.)) Unlike geolocators, which have to be retrieved from the birds, satellite trackers transmit location data to satellites in real time or at programmed intervals.

Six trackers never transmitted and one bird stayed on Mo‘orea. The 13 remaining birds departed to the northwest 10-26 April and ten arrived in Japan: seven by non-stop flights, while three took breaks on one or two islands east of Japan.

Ten birds departed Japan in mid-late May for Alaska. Unlike Samoan birds four Mo‘orea birds flew to eastern Siberia where three trackers failed and one nested. The other five, like Samoan plovers, flew to southwest Alaska where they nested. Four more contacts were lost, and the remaining two plovers were recorded leaving Alaska. The 21^st August departer flew 1,500km southeast before being lost. The other plover left Alaska on 8^th September and flew in eight days to Samoa where transmission ceased two weeks later. It is not known if the bird continued to Mo‘orea.

Despite the probable tracker transmission failures, the researchers were surprised to not subsequently find any of their colour-tagged birds on Mo‘orea. Previous research in Samoa and in Hawai‘i showed that plovers had a strong tendency to return to their former territories in the Pacific. They offered two hypotheses that might apply to plovers residing near their migration limit: (1) they took much longer to arrive because they did some island-hopping, as did the plover tracked to Samoa; or (2) they were less site-faithful and therefore difficult to relocate on Mo‘orea.

The Mo‘orea research is a good proxy for the migration of Cook Islands Tōrea and it will be interesting when they discover more about their southbound routes.

New Zealand Kuriri

In early 2019 and 2020 nine plovers were fitted with satellite trackers at the Pūkorokoro Miranda Shorebird Centre on the west side of the Firth of Thames.(( https://shorebirds.org.nz/shorebirds-at-miranda/wheres-goldie-following-pacific-golden-plover)) Would they fly 9,000km non-stop to Japan and, two, would they fly 10,500km non-stop from Alaska to New Zealand?

Five transmitters never transmitted. The four remaining birds departed on the 4^th, 8^th, 13^th and 23^rd April. Three flew to Japan and one flew to coastal China to feed. The three to Japan took 7, 8 and 9 days. Seven days for 9,000km is indicative of a non-stop flight.

In Alaska contact was lost with two birds and the other two eventually departed southward. Jojo, a 2019 male bird, spent a month on Teraina (Washington) north of Kiritimati, followed by three weeks on Tongatapu when its transmitter lost power on the 19^th November. Imagine the excitement when Jojo was spotted at Pūkorokoro on 15^th March 2020 – the first plover to be tracked to Japan, Alaska, and back to Aotearoa.

One of the 2020 birds, Ra also headed south after nesting in Alaska. She left Alaska on the 7^th October and covered the 4,000km to Hawai‘i in a mere two days! She then flew 5,000km southwest to Tikopia, the southernmost island of the Solomons, and then 500km south to near Port Vila on Efate in Vanuatu where contact was lost on the 5^th Nov. Of course, everyone is watching for Ra in Aotearoa.

Summary

Hawai‘i plovers fly to Alaska on a direct non-stop 4,000km flight of about 3 days. After breeding they fly the same direct route home to occupy their original non-breeding territories.

South Pacific plovers migrate along a clockwise route with the first stop in Japan, where they feed around the rice fields for about three weeks. The longest non-stop flights to japan were recorded for Mo‘orea plovers, covering 9,500km in about eight days.

After Japan, South Pacific plovers almost all nested in southwest Alaska, with a few in eastern Siberia. As soon as the young are capable of feeding themselves, the adult birds desert them and fly to the Peninsula and Aleutians to gorge themselves to deposit enough fat for the long flight ahead. The ten Samoa plovers all made direct non-stop flights south to Tutuila. The data for Mo‘orea and New Zealand plovers was inconclusive, mainly due to equipment inadequacies. The southward island hopping migration of the one Mo‘orea  plover and the two New Zealand birds is yet to be demonstrated as typical.

If Marquesan plovers 1,500km northeast of Mo‘orea also go direct to Japan rather than Alaska, would this throw doubt on the popular idea that ancient Marquesans found Hawai‘i by observing the migration direction of the Tōrea?

The great circle route from the Marquesas is 307° to Japan and 350° to Alaska. Hawai‘i is midway between these routes at 330°. The idea that the Tōrea showed the way to Hawai‘i still works.