🦫 #13 answers: Animal Lives Day

Owls can't move their eyes in their sockets, so they turn their whole heads to change where they look.

Their eyes are tube-shaped, which leaves no room to swivel.

“Owls have binocular vision, but they must rotate their entire heads to change the focus of their view because, like most birds, their eyes are fixed in their sockets.”

Pit vipers have heat-sensing pits on their faces that let them find warm-blooded prey in the dark.

The pits detect infrared, a 'sixth sense' for body heat.

“These loreal pits are the external openings to a pair of extremely sensitive infrared-detecting organs, which in effect give the snakes a "sixth sense" to help them find and perhaps even judge the size of the small, warm-blooded prey on which they feed upon.”

The world's largest beaver dam, nearly a kilometre long, was discovered using satellite images.

It's about 850 metres long, in Wood Buffalo National Park in Canada, so remote that it was spotted on satellite images.

“In 2007, the world's largest beaver dam – about 850-metre (2,790 ft) in length – was discovered in the park using satellite imagery.”

Male satin bowerbirds decorate their stick bowers with colourful finds, including pens, drinking straws and clothes pegs.

They especially love blue objects, which stand out against their stick bowers.

“Males build specialised stick structures, called bowers, which they decorate with blue, yellow, and shiny objects, including berries, flowers, snail shells, and plastic items such as ballpoint pens, drinking straws and clothes pegs.”

A pufferfish only about 10 cm long builds circles two metres across, a huge construction job for its size.

He sculpts the ridges with his fins and decorates them with shells. The female inspects his work before laying eggs.

“Each circle, two meters in diameter, has a huge cost of construction for the relatively small (10 cm or 3.9 in) fish.”

The diving bell spider can stay underwater for long periods thanks to a silk structure that holds its air supply.

It's the only spider known to do this. The silk 'bell' traps air like an underwater tent.

“A. aquatica is able to remain submerged for prolonged periods of time due to the silk-based structure it constructs in order to retain an oxygen supply, named after the diving bell structure it resembles.”

The common tailorbird pierces the edges of a big leaf and sews them together with plant fibre or spider silk.

The sewn leaf makes a cradle, and the actual nest is built inside it.

“The edges of a large leaf are pierced and sewn together with plant fibre or spider silk to make a cradle in which the actual nest is built.”

Paper wasps make their nests by mixing fibres from dead wood with saliva, creating a kind of paper.

The result looks a lot like grey or brown handmade paper.

“The wasps gather fibers from dead wood and plant stems, which they mix with saliva, and use to construct nests that appear made out of gray or brown papery material that is very similar to handmade paper.”

Bald eagle nests can grow up to 4 metres deep and weigh as much as a tonne.

They're the largest tree nests ever recorded for any animal.

“It builds the largest nest of any North American bird and the largest tree nests ever recorded for any animal species, up to 4 m (13 ft) deep, 2.5 m (8.2 ft) wide, and 1 metric ton (1.1 short tons) in weight.”

One prairie dog town in Texas was reported to cover 64,000 square kilometres and hold 400 million animals.

That's a historical report from when prairie dogs were far more common.

“A black-tailed prairie dog town in Texas was reported to cover 25,000 mi2 (64,000 km2) and included 400,000,000 individuals.”