THINKING ABOUT EGGS

Eggs are forefront in our mind at Easter, of course, but maybe not those of wild birds. Happily, unlike during the Victorian era, birds and their active nests are now very strictly protected in law in the UK. This means, however, that fewer people have seen many wild birds’ eggs unless they have visited a museum collection or watched a natural history film about them[1].

We are fortunate in having a good series of original photos of British birds’ eggs of which a few are pictured here (see below to work out what they are) but first a few egg facts:

• Eggs provide all the necessary nutrients (proteins, fats and vitamins) required for embryo development during incubation.
• The main components of birds’ eggs are the shell, membranes, albumen (the egg white) and the yolk. The calcium carbonate shell is porous for gas exchange, protective and lends structural integrity. The pointy shape of some eggs, especially seabirds’ on cliffs, helps to prevent their rolling off the nest area. The shells’ colours, often complex and beautiful, are species-specific and may help to camouflage the eggs in some situations. Anything between one and twelve eggs may be laid, dependent on species – and size is very variable (think hummingbirds and emus!). The outer and inner membranes of the egg help to prevent loss of moisture and are protective against pathogens. The albumen is a further defence against pathogens, provides protein and cushions the yolk. The yolk is the food for the developing embryo.
• For incubation, a temperature that is consistent is vital. Typically this is between 37.5°C and 38.5°C and maintained by the sitting bird.

Do you know to what birds the six eggs pictured belong? Here they are in order from top of page but in anagram form for you to work out: hedcluks, wecrul, hormone, lirc tingnub, rabn wolslaw and dratters (not to scale)[2].

Betts Ecology keep notes about nesting birds on our sites and we ask residents to take care not to disturb birds that are making nests, brooding or feeding young.

HAPPY EASTER TO ALL!

[1] For example, Sir David Attenborough’s Wonder of Eggs which is still available at https://www.bbc.co.uk/programmes/b09yj7dx

[2] Please note the example photos in this article are from our own library and are copyright.