Bright blue eggs, why ?

[mrbright]

whilst meandering around my parents garden, unfortunately came across a lot of predated eggs, thrushes, blackbirds, and hatched robin eggs, all blue, can anyone explain why so many of our garden songbirds have very obvious bright blue eggs, surely this makes them easy to spot for predators. have googled but to no avail, theories anybody.

[loripo]

A Q & A page on the RSPB website says...
Birds that lay their eggs in the open or on the ground, such as the lapwing, rely on their eggs being well camouflaged. This camouflage takes the form of coloured spots or patterns, which blend into the surrounding ground cover.

Birds that lay their eggs in holes or anywhere where dark, such as a kingfisher, are likely to have eggs that are either white or pale blue and this helps the birds locate them.
The eggs of the great crested grebe can actually change colour during incubation. These eggs start off a bluish white colour and after being in contact with the water plant-based nest material, these eggs turn a brownish colour.
Despite the variations in bird egg colour, there are in fact only two pigments, which are responsible for bird egg colour. Oocyan, which derives from bile, is responsible for blue and green shades and Protoporphyrin, a blood derivative, is responsible for spots, patterns and some general colour.

[RKB]

Doesn't really account for Dunnock though, does it.

Nobody is really sure, but it must be remembered that birds and mammals don't necessarily see colour in the same way that we do. Many mammals only see a kind of greyscale, and many birds see near-ultraviolet.

A nest is more obvious than a few eggs (as it's much bigger), so egg camouflage maybe isn't very important for cup-nesters (as the eggs aren't visible for very long anyway, being sat on most of the time). The variation of Guillemot eggs shows what can happen when the pressure is off, as they are a huge variety of colours.

Also, pigment has been shown to be structurally important in tit eggs, so maybe has a similar function in other species.

Finally, egg colour may be a hang-up from the behaviour of ancestors, which perhaps nested differently. Egg colour maybe didn't change because it didn't have to as doing so conferred no benefit. And many passerines have also been in an arms race against nest parasites like the Cuckoo (where there many others in recent geological time, like in modern Africa?), so egg colour may be a trade-off between all of the above and making it easier to spot a parasite egg.

[poschiavanus]

You're not alone in asking this question. The colour of birds' eggs has fascinated scientists for a long time. Alfred Wallace (co-discoverer of Natural Selection) wrote about the issue in 1882.

For a recent scientific review (which may be overly technical for some) I recommend a paper by Kilner (2006) in Biological Reviews. The PDF is available at this link.

[astarsdad]

Hi,
I don't know what it is about this forum, but a lot of people think robins eggs are blue and they are not. They are about the size of a penny, oval rather than round and are pale white or very pale blue with brown speckles/blotches around the top, decreasing towards the bottom.
????I now know why people think this way. I googled 'robins eggs' and the results produced results for the 'amrican robin'.
Terry

European Robin - Wikipedia, the free encyclopedia

[mrbright]

many thanks for the input, all very helpfull, i will endeavour to read up a bit more with your suggestions, but if its baffled some scientists for years, i probably dont stand a chance, however maybe magpies are the exception to the rule on colour vision, as they appear to be the culprits. again ,thanks.

[mrbright]

[quote=astarsdad;618989]Hi,
I don't know what it is about this forum, but a lot of people think robins eggs are blue and they are not. They are about the size of a penny, oval rather than round and are pale white or very pale blue with brown speckles/blotches around the top, decreasing towards the bottom.
????I now know why people think this way. I googled 'robins eggs' and the results produced results for the 'amrican robin'.
Terry

quite right terry, just googled myself, in which case i will revise my 3rd hatched egg as a starling far more chance of that, but i must admit i always thought robins eggs were blue, now we know why.

[RKB]

Starlings are one of the most distinctive eggs. They are a very pretty powder blue, similar to the colour scheme around the edge of this website. They are also quite pointed at one end (more so than e.g. Blackbird).