In general, there are two forces - selection for bigger males if there is competition between them for females, and fecundity advantage hypothesis - larger females produce more offspring. Personally, I don't see any reasons for males in ravens to be bigger - they are monogamous, do not compete for females or resources...

Corvus corax are relatively large birds that display monogamous behaviors. Their eggs are generally preyed on by larger birds, such as owls and eagles. I personally think that the males tend to be larger in order to support its female counterpart in protecting their young. Their larger size also prevent predators from preying on them, thus increasing the chances of being able to protect their offspring.

Hi.

I think you can find some information on the subject in the superb book about the species written by Derek Ratcliffe:

RATCLIFFE, D. (2011). The Raven: A Hatural History in Britain and Ireland. T & AD Poyser Ltd (A & C Black). London. 326 pp. 

Why are females smaller?

Hi again.

See also the information on the species contained in the next scholar book:

CRAMP, S. & C. M. PERRINS (eds.) (1994). The Birds of the Western Palearctic. Vol. VIII. Crows to Finches. Oxford University Press. 899 pp. + egg plates. 

(Pages 206-223 are devoted to the Northern Raven Corvus corax)

Two possibilities:

1. Sex-linked genetic phenomenon in morphology.

2. Diet- before and after the birth.

These two factors are mostly considered for the dimorphic situation in any species !!

Hi Ksenia,

please find a couple of potentially useful papers at the following links:

http://www.researchgate.net/publication/227619049

http://www.researchgate.net/publication/238033047

not the same species, but I guess sexual dimorphism is similar across corvids and so should be  the remote causes that determine it.

I hope this helps, all best

Danilo

Article Morphology and sexual dimorphism of the New Caledonian Crow ...

Article Geographic variation in size and sexual dimorphism across a ...

Thank you! 

Very interesting papers by NicolaSaino & FiorenzaDeBerardi, and Benjamina et. al.. Thanks and greeting to both team