The pathways of migratory birds may have helped in the discovery of new lands. There were certainly people who were familiar with patterns of bird migration. For example, the direction of the West Polynesian pigeon’s annual migration was followed by navigators between Tonga and Samoa. Ancestors of the Māori may have speculated that there was land in the south-west Pacific, as the long-tailed cuckoo and shining cuckoo fly south from the islands of Polynesia and Melanesia respectively every spring and return in autumn.
Land is signalled by the birds that fly out to sea at sunrise to fish, then return to their nests at sunset. Frigate birds fly up to 100 km from land, gannets and petrels 70 km, and terns up to 50 km.
At the beginning of each winter the humpback and other whale species travel in multiple family groups, or pods, as they migrate north from Antarctica to the Pacific. Some pass along the west coast of New Zealand into the waters of Vanuatu and New Caledonia. Some travel along both sides of the country toward Tonga and Samoa, while others pass the east coast to Rarotonga and Tahiti. In November and December, the whales return south to Antarctica.
Māori ancestors may have believed that by following whales they would be led to land, as whales typically calve in the calmer waters off atolls, islands or larger land masses. Because they are slow, whales would have been easy to follow. Their rate of travel, three to five knots, is well within the cruising speed of a double-hulled canoe. According to Māori oral traditions, whales guided canoes to New Zealand, and the ancestor Paikea is even said to have arrived on one.
The season when whales migrate south coincides with the appearance of the stars and planets most useful for navigating to New Zealand – the setting sun, Kōpū (Venus), Te Waka o Tamarereti (Scorpio) and Māhutonga (the Southern Cross).
Zenith stars that at their highest point shine directly over known islands were useful for locating land. They were used by Tongan, Tahitian and Tikopian navigators. Arcturus is the zenith star for Hawaii, and Sirius for both Ra‘iatea in Tahiti and Vanua Levu in Fiji. Navigators positioned their canoes immediately beneath their target star, knowing that this would place them within 80 km of the destination island.
Measuring the height of meridian stars (stars on the same longitude) above the horizon using fingers and hands was a useful method for finding land. Polynesian sailors may have been guided by meridian stars such as the Southern Cross. For instance, viewed from Hawaii the bottom of the upright Southern Cross is four fingers above the horizon; sailing south it increases to one full hand span at the equator, and two hand spans approaching the latitude of Tahiti.
The shape, movement and colour of clouds were important indicators of land. Convection clouds build up during the day over large islands, becoming higher, thicker, darker and slower moving than clouds over the sea. Cloud over high islands such as Tahiti and Hawaii can be seen over 150 km away. The small, characteristically eyebrow-shaped clouds that form over small atolls can be seen up to 50 kilometres away. A reef is indicated by pinkish cloud, while the cloud base over forested islands is dark or green. When a cloud is unusually bright, sunlight is being reflected off atoll lagoons onto the cloud base.
Experienced navigators used distinctive land-swell patterns, which form when sea swells strike land, to determine the location of land long before it was visible. Land-swell patterns have two distinctive forms. In one, waves take shape when the prevailing swell strikes an island and bounces back on itself. Bounce-back waves can be detected 50 km away from small islands, and up to 300 km away from land masses the size of New Zealand. In the other land-swell form, patterns are created when a swell divides and curls around an island. Navigators can detect the confused wave pattern or shadow of turbulence at some distance.
The sea itself provided useful markers for navigation. Changes in colour, the presence of certain fish species, ocean currents, the ‘scent of land' and the appearance of whirlpools were all important signs. Debris such as driftwood and leaves suggested nearby land, and floating rubbish signalled that a settlement was close.