Identifying male/female Cormorants ( Dodder river, Ireland) (1 Viewer)

[keps]

Is there a way to distinguish between a male and female cormorant?

For instance this is a pic I took today. As a guesss I would say the bird with the whiter head feathers is a male- but that's all it is- a guess.

 

[Butty]

No. What you see there is due to differing stages of moult and the acquisition of breeding plumage - possibly age as well. Your field guide will show you that male and female are identical.

 

[KenM]

Your field guide will show you that male and female are identical.

With the exception of their nether regions 😂

 

[KC Foggin]

I've always wondered that myself keps.

 

[RafaelMatias]

Males will be larger on average (on this species and other Phalacrocoracidae, perhaps extendable to all Suliformes). In a breeding pair (on the nest) the difference is obvious, with males with clearly larger head, more robust neck and body (females tend to pair with larger males). However, outside of the nest (of a pair) this should not be attempted, as you could be seeing a large female with a small male.

 

[Butty]

In a breeding pair (on the nest) the difference is obvious, with males with clearly larger head, more robust neck and body (females tend to pair with larger males). However, outside of the nest (of a pair) this should not be attempted, as you could be seeing a large female with a small male.

If large females are indeed larger than small males, sexing at the nest cannot be any more reliable than with a random couple of birds - otherwise it would be necessary that females deliberately avoid pairing with males smaller than themselves, i.e. that large females select only males larger than themselves - which seems unlikely.

 

[RafaelMatias]

females deliberately avoid pairing with males smaller than themselves, i.e. that large females select only males larger than themselves - which seems unlikely.

Which is exactly what happens, why is this surprising. It's called assortative pairing, it's well known on loads of animal species.

EDIT: I skipped over the word "only". No, it is a tendency, certainly, but the word "only" would mean there would be no exceptions, which is not what I meant.

 

[Butty]

It's called assortative pairing, it's well known on loads of animal species.

👍🏻 Now you mention it, I've noticed a similar thing in breeding pairs of great crested grebes.

 

[Alexander Stöhr]

Yes, I agree with Rafael and Butty. It can be obvious in large Gulls, too.