10 Whale sharks

The world’s largest fish was once considered to be a solitary giant, but recently its reputation as a loner has been turned on its head. Large aggregations of whale sharks, which can grow to be 12 metres long, have been discovered off Mexico’s east coast, most notably just east of the Yucatán Peninsula, where 420 sharks were seen during a single aerial survey in 2009. Scientists found that the so-called ‘Afuera’ aggregation was feeding on dense patches of fish eggs.


The Afuera whale shark aggregation was reported in Deep Sea News

9 Wildebeest

The famous wildebeest migration in Africa’s Serengeti is actually a vast, endless clockwise rotation of, yes, wildebeest, but also zebras, gazelles, eland and impalas comprising an estimated 1.5 million animals. You won’t see them all at once, of course, but where should you go to get the greatest numbers? Well, arguably it would be the point where they have to cross the Mara River – tour operators say 10,000 wildebeest crossing in one day is not unusual, while 100,000 has been recorded.

8 Common dolphins

Aggregations of dolphins can be among the largest of any marine mammals in the world. Pods or groups of 1,000-2,000 short-beaked common dolphins have been reported off the coast of Pembrokeshire, in Wales, on several occasions, while groups of bottlenose dolphins of 3,000-5,000 animals have been seen off Costa Rica. But an event off San Diego, California, in 2013 trumps both of these – a school of common dolphins said to be 11km long and 8km wide and consisting of an estimated 100,000 animals.

Watch this video of the dolphin 'super pod' off California

7 Snow geese

Snow geese are one of the most successful species of bird on the planet: not only are there some 15 million of them, but their population has increased by an estimated five-fold or more in the past 30 years. They migrate between their breeding grounds of the northern Arctic tundra and the overwintering grounds in the southern and eastern USA. Squaw Creek National Wildlife Reserve recorded 126,000 geese during a bird count in mid-December 2015, though numbers can reach up to 400,000.

The US Fish & Wildlife Service has more information about Squaw Creek NWR

6 Amur falcons

Amur falcons do the longest migration of any raptor, travelling some 22,000km from Somalia, Kenya and South Africa to East Asia and back again every year. They also do it in huge numbers, with estimates as high as 1 million birds undertaking the trip. During their journey, they all end up at Doyang reservoir in Nagaland in the extreme north-east of India. In 2012, the Indian authorities discovered the birds were being killed for consumption and sale at a rate of 120,000-140,000 birds a year, but prompt conservation action was swiftly able to put an end to the slaughter.

Conservation India was closely involved in stopping the illegal killing of the Amur falcons

5 Starlings

In the UK, these small songbirds are renowned for forming huge flocks, known as murmurations, in the hour or so before sunset during late autumn and winter. In Denmark, spring and autumn starling murmurations are said to be even more spectacular, forming flocks of up to 1.25 million birds in some places on Jutland’s west coast – Ribe and Tonder Marshes have some of the biggest numbers.

The Danish Ministry of Environment’s Nature Agency has information (in Danish, but you get the gist) on murmurations in Jutland. Discover the best places to see starling murmurations in the UK.

4 Atlantic puffins

During the summer, Iceland is home to an estimated half of the entire Atlantic puffin population - somewhere between 3 and 4 million pairs go there to breed and raise their young, of which an estimated 1.5 million or 3 million puffins can be found in the Westman Islands (Vestmannaeyjar) of the south coast. Látrabjarg Cliffs in the Westfjords (Vestfirðir) – on Iceland’s westernmost tip – are also renowned for their huge seabird colonies, including puffins, razorbills and guillemots.

Find out more about the Westman Islands

3 Straw-coloured fruit bats

Africa’s greatest migration doesn’t involve wildebeest or, indeed, a creature with four legs, though it is mammalian. Every November and December, between 5 and 8 million straw-coloured fruits bats take up residence in Kasanka National Park, Zambia, to feed on seasonal supplies of fruit. Not only that, but it’s said they settle for their feast in just 1ha of the park’s mushitu swamp forest. Just how many of these you can see is anybody’s guess, but one tree is said to hold 10 tonnes of roosting bats.

Kasanka Trust has more information on the bats

2 Mexican free-tailed bats

Despite the prodigious numbers of straw-coloured fruit bats in Africa, there’s a single cave in Texas, southern USA, that has even higher numbers – Bracken Cave, which between March and October every year is home to some 20 million Mexican free-tailed bats, the largest known bat colony in the world and probably the largest concentration of mammals on Earth. They emerge each evening to feed on insects and are remarkable in other ways, too: they can fly at speeds of more than 90kmh and at altitudes of more than 3km.

Bat Conservation International has helped to preserve Bracken Cave and the bats’ surrounding habitat

1 Monarch butterflies

Every year, monarch butterflies travel some 4,000km from their summer breeding grounds of the northern USA and Canada to their overwintering sites in the fir tree forests of the central Mexican state of Michoacán. They are remarkable not just for this lengthy migration, but the sheer numbers in which they do it – in the winter of 2014-15, an estimated 56.6 million butterflies descended on the Reserva de la Biosfera Mariposa Monarca. That is, however, quite a decline from the 909 million that were thought to have been there in 1996-97. Habitat loss, climate change and the use of pesticides are the main factors in the monarchs’ decline.

The Monarch Joint Venture project is working to protect monarch butterflies throughout their range


Main image: Wildebeest gather before crossing the Mara River in the northern Serengeti. © Prasit Chansarekorn/iStock


James FairWildlife journalist