Every year, in early April, a large tere party leaves the Cook Islands for Alaska. They are in their most spiffy clothes to attend the great Alaskan courtship party. They are in the Tōrea tere.
Our understanding of the group’s itinerary changed dramatically in 2012 when it was revealed they detour to a long feast in Japan on the way to Alaska. In this article we show how many years of research has gradually unraveled the migratory life of the Pacific Golden Plover.
Cook Islands Tōrea
During our summer the Pacific Golden-Plovers (Pluvialis fulva) are the drab brown birds on open grassy areas and along the shoreline. They alternate between standing motionless and jogging a few metres, and periodically they peck at an insect or other food on the ground. Each is usually the solitary occupant of a large feeding territory, although they sometimes form small groups. When they take flight they often give a repeated “tuuu-ree” alarm call.
Traditional names for the plover imitate its alarm call: Tōrea (Rarotonga, Mangaia, Aitutaki, Manihiki, Rakahanga, Societies and Tuamotu), Toretōrea (Ātiu, Ma‘uke and Miti‘āro), Tuli (Penrhyn, Pukapuka, Nassau and Samoa), To‘ea (Marquesas), and Tusiik, Turiik or Tullik (Eskimos Alaska).
The only local study of the Tōrea was undertaken by Natural Heritage from 1994 to 1997. Each week in the late afternoon we counted the birds and recorded their plumage. The graph shows the results.
The study showed there were 200-300 plovers on Rarotonga, with about 140 living on the airport grounds, mainly in defended feeding territories on grassed areas. During the day the other plovers on the island were scattered along the shore and on grassed areas, such as large lawns and playing fields.
The birds on the airport were relatively secure from cats and dogs and they slept in their territories at night. Birds in less secure grassed areas flew to safer roosting areas for the night, such as the motu in Muri or the ends of the airport runway.
During our winter, from May to July, there were less than five plovers on the airport. Around the end of July the first birds arrived back from Alaska in breeding plumage and the number of birds increased steadily throughout August, September and October.
Around the end of September the number in breeding plumage decreased and by mid-November all birds had moulted into their drab non-breeding plumage. During February most birds moulted again, changing their drab brown feathers for their spiffy black and white front and golden speckled back and wings.
During the first two weeks of April flocks of birds were seen flying around the airport area and in stages the number decreased as they departed the island for Alaska. No actual departures were seen.
When the plovers arrive in Alaska, Spring has arrived; the snows are melting, plants are producing berries and fruits, and insects are emerging.
On the dry tundra hills above the bush-line, most male plovers return to the same nest they used the previous year, or nest nearby. In their aristocratic manner they perform dramatic aerial displays to attract a new mate, because females do not usually return to previous nest sites.
If all goes well, the new couple rebuild the nest with moss and lichen, she lays four eggs, and they share the role of incubating them until they hatch after 25 days. Most hatchlings emerge during the two weeks of July.
Within a few hours of the last egg hatching the youngsters are running around looking for food with parental guidance.
Moving about also gives them a better chance of avoiding predators such as foxes and predatory birds. In three or four weeks the young can fly and the adults desert them to fly south to better feeding areas on the coast to fatten before migrating southward to various islands in the Pacific.
In early September the juveniles detect falling temperatures and diminishing food in the high country and they fly south to the richer feeding areas along the coast. Around the third week of September they depart southward on their first transoceanic flight with the nearest islands, the Hawai‘i archipelago 4,000km away.
They don’t all stop in Hawai‘i with a sigh of relief. Research has shown that many juvenile first year birds arrive on islands in the South Pacific, 4,000km south of Hawai‘i.
Studies on Niue in the early 1970s found that first year birds did not change their plumage or migrate to Alaska with the adults in April. Most undertook their first northward migration a year later when they were 18 months old, with some postponing a further year. We would expect the juveniles on Rarotonga to follow this pattern.
The Hawai‘i Kōlea
The details of the migratory life of the plover have been revealed slowly over the last 30 years by the persistent research of Oscar (Wally) Johnson and his team. They initially focused on the plovers on Oahu in Hawai‘i and in Alaska, and more recently extended their work to Micronesia and American Samoa.
In April 1996 the Johnson team put radio transmitters on 20 Kōlea on Oahu. Using radio receivers they relocated three breeding in southwest Alaska, the first direct evidence that Hawai‘i plovers nested in Alaska.
This and other research showed that on Oahu both males and females reoccupied the same feeding territories as the previous year; and in Alaska the males reoccupied the same nest as the previous year or rebuild nearby, while females usually wandered around and found a new mate.
The Samoa Tuli
In 2007 the Johnson team put radio transmitters on 30 Tuli on Tutuila in American Samoa and 10 Kōlea on Oahu.
Samoan birds mainly migrated during the second week of April while Hawai‘i birds left two weeks later in the fourth week of April. Both groups averaged about 180g at departure consisting of a fat-free weight of 105g and 75g of fat fuel. Despite the much longer migration for Samoa birds their survival rate after one return migration to Alaska was 83 per cent (25 birds), which was similar to Oahu birds at 86 per cent
The excellent one-year survival rate of Samoan birds means the earlier 20 years of survival research on Oahu probably applies to Samoan birds. On Oahu, of 78 adults of unknown age with territories, 53 per cent (41 birds) survived three years, 26 per cent (20) survived six years and 13 per cent (10) survived nine years. The longest surviving bird lived 17years! Non-territorial birds had a much lower survival rate.
The 2007 Samoa research concluded that the birds probably migrated northward on a bidirectional Central Pacific flyway with a stopover, probably in the Hawaiian islands, so they would arrive in Alaska in early May when the snows are mainly melted - as do Hawai‘i plovers.
As a second possibility the researchers wondered if Samoa birds might stopover in Japan, using a unidirectional clockwise flyway as had been demonstrated in 1973 for Central Pacific Ruddy Turnstones, a similar sized shorebird to the plover.
Kōlea migration unravelled
The next big knowledge breakthrough was published in 2011 analysing data from geolocators deployed on 24 Kōlea on Oahu in April 2009 and 2010. Geolocators do not give real-time locations via satellite but when retrieved they can show the geographical position of each bird at 12 hour intervals.
Most Kōlea left Oahu in the fourth week of April (18/3-4/5). They arrived in southwest Alaska around the beginning of May (22/3-10/5) to find the snows mainly gone and rapidly increasing supplies of insects and small fruits. The northward non-stop flights zigzagged with actual flight paths of 4,000 to 6,400km taking 1.8 to 4.3 days, averaging 3.2 days. (See the bidirectional Hawai‘i-Alaska flyway on the map.)
After raising their young the adults left the breeding grounds July 3 to August 24 and flew to southern coastal areas to feed for one to 40 days before flying to Hawai‘i. They arrived on Oahu during the second and third weeks of August after an average non-stop flight of four days. The zigzag flight paths varied from 4,000km to 7,300km.
Two birds passed east of Hawai‘i and continued south for 550km and 850km before backtracking to Oahu, adding 30hrs and 42hrs to their journeys. These were very energy costly errors and it would be interesting to know what caused them.
The average ground-speeds for the 12-hour sectors varied enormously from a very slow 15km/hr to a whopping 185km/hr, presumably the former into a headwind and the latter with a tailwind. One bird on a northward flight had an average 12-hour ground speed of 26, 21, 46, 185, 85, 17 and 35 km/hr. It flew a zigzag course of 5,000km at an overall average ground-speed of 59km/hr to arrive in Alaska in 84hrs (3.5days).
Most research on the ground-speeds of individual birds has shown they have an overall average 60-65km/hr for non-stop flights of two to eight days.
Finally, in 2011, after more than a 100 years of theorising and dozens of years of indicative evidence we had accurate information on the migratory life of the Kōlea of Oahu.
South Pacific and Micronesia
The Johnson team deployed geolocators on 18 males in Nome, Alaska in June 2009 and 2010 with eight recovered after a year; and on 19 plovers in American Samoa in March 2010 with 10 recovered seven months later.
The results published in 2012 transformed our understanding of South Pacific plover migration from the commonly assumed bidirectional north-south Central Pacific flyway into a unidirectional clockwise flyway, as previously proven for Ruddy Turnstones.
The clockwise transoceanic migration of the Samoan birds started during the second week of April with a six-day non-stop flight to Japan were they feasted for about three weeks on the invertebrates in the rice fields. They departed Japan May 13-17 and arrived at the breeding grounds in western Alaska and eastern Siberia May 16-20, after an average flight time of 3.5 days. (See map for more details.)
After breeding, they made a short southward flight to fatten themselves on the southern coast of Alaska for about three weeks. They then flew non-stop southward on a Central Pacific flyway to Samoa over zigzag paths of 8,000km to 12,300km taking 5,0 to 7.5 days with an average of 6.5.
The Nome tagged birds also used the southward Central Pacific flyway before dispersing to a variety of islands in Micronesia, the Line Islands (Kiritimati, Christmas) and Fiji (Viti Levu and Kadavu). Non-breeding plovers are widespread in the South Pacific being distributed from the Marquesas and Pitcairn in the east to the east coast of Australia and the main islands of New Zealand in the west.
Rarotonga plovers leave for Alaska around the same time as the Samoa birds and we can assume they use the same flyway to Japan before going to Alaska, where they probably nest with Samoa birds well north of the breeding area for Hawai‘i birds. In March this year the Johnson team put satellite trackers on plovers in Mo‘orea which shed more light on the behaviour of Cook Islands birds.
Alaska has about 20,000 breeding Pacific Golden Plovers, while there are more than 200,000 in northern and eastern Siberia. Although a few Pacific island plovers nest in estern Siberia, most Siberian birds take their non-breeding holidays in tropical Asia and Australia and Melanesia, westward to India and islands in the Indian Ocean. They migrate over land and have several favourite feeding areas along the way.
In 2015 scientists showed that plovers going to tropical Asia were physically distinguishable from those going to the Pacific Islands. They proposed splitting the species into two subspecies: Pluvialis fulva fulva, the Pacific Golden Plover; and, Pluvialis fulva johnsoni, after Wally and Patricia Johnson, the Asian or Siberian Golden Plover.
The discovery of Hawai‘i
Legends and scientific information about the discovery and settlement of Hawai‘i indicate it involved navigators from Tahiti and the Marquesas around 1200 AD.
However, Hawai‘i oral traditions give no reasonable account of how such navigators in French Polynesia were so convinced there was land to the north that they persisted on voyages of 3-4 weeks to find it.
Since the 1920s it has become increasingly popular to think that the mass northward migration of golden plovers, which cannot land on the ocean, would have proven there was land to the north of French Polynesia.
At present it is not known if Marquesan To‘ea depart northward to go via Hawai‘i to Alaska or if they depart northwest to Japan. If it is shown that they go northwest to Japan could they still have been the inspiration to ancient navigators to search northward for land and eventually find Hawai‘i?