Half a dozen egg facts!

Three blue tinged grey heron eggs lie in their nest made from twigs

Want to know some UK bird egg facts? Here’s half a dozen to casually drop into conversation this Easter, just to prove you’re a real egg head. CAUTION: You may encounter further egg puns beyond this point.

Three blue tinged grey heron eggs lie in their nest made from twigs

Smallest egg…

No real surprise that the smallest egg belongs to our smallest bird – the goldcrest. The female lays between seven and ten little white eggs with brown speckles, each weighing less than 1g. But if you consider a goldcrest weighs about 6g, around the same as a 5p coin, the eggs really aren’t that tiny, with some clutches weighing more than her!

Most bird eggs are in keeping with the size of the female bird – but there are exceptions. For example, the cuckoo, who weighs around 100g lays eggs that are around 4g. The eggsplanation for this is so their eggs resemble the eggs of the nest they lay them in, with the host birds much smaller than the cuckoo.

Largest Egg…

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Don’t worry, we won’t eggs-agerate. The largest egg is also the heaviest and belongs to the mute swan. These are around 113mm in length and 74mm in width, weighing on average 340g. The whooper swan isn’t far behind, with a similar size and weighing 331g. The crane, which is our tallest bird, has smaller eggs than you may think, weighing on average 195g.

Of course, these all seem rather small to the ostrich, which has the biggest egg in the world. These can weigh up to 1.6KG.

Largest brood…

For some birds it makes sense to play the numbers game. Gamebirds, such as pheasants, mallards, and red legged partridge are all at the egg-streme end of the scale, usually laying between 10-16 eggs. Moorhens have been seen laying up to 20. The size of the bird doesn’t seem to matter, with some of our biggest birds, such as the grey heron and mute swan, often laying more than ten, as do some of our smallest, such as the goldcrest and many of the tits.

Oddest shape…

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The Guillemots’ egg is beautiful blue but it has baffled experts for hundreds of years as to why it is so pointy. Some said it was to make them spin easier when knocked, preventing them falling into the sea from their cliff nest sites. Others said it was to make them roll in an arc. But in 2018, experts from the University of Sheffield cracked it. They revealed the shape made them much more stable when they are laid on an angled surface, such as the steep rugged and rocky nest sites guillemots prefer.

Longest incubation…

The golden eagle comes out top here, with its eggs usually taking 45 days to hatch. They are closely followed by many of our big birds of prey, including the white-tailed eagle, buzzard and marsh harrier, as well as other large birds like the mute swan and crane.
For our smaller birds, swifts take a little longer than most to hatch, up to 20 days.

First to lay…

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Scottish Crossbills need no egging on. They are one of the earliest birds to lay despite living in the colder climate of the Scottish Highlands. These beautiful bulky finches can lay as early as February, with the eggs especially resistant to cold temperatures. The reason for the early laying is to time the arrival of the chicks with the best time for pinecones, their favourite food.