True Hawks

By Daniel Butler, author and forager

This is nothing to do with mushrooms, but those who love the great outdoors might be interested in a few casual observations about ‘true’ hawks: members of the Accipiterae.

There are many spread around the world, but Britain has two: the sparrowhawk and its bigger relative, the goshawk. The first is now our commonest raptor, beating first the kestrel and later the buzzard for the top spot over the past 25 years.

A female sparrowhawk (spar) is roughly the size of a dove

(Photo: author’s own)

The sparrowhawk is interesting in having the biggest reverse sexual dimorphism amongst British raptors. This rather pompous phrase refers to animals where the female is considerably bigger than the male. A male (musket) typically weighs about 140g and is about the same size as a male blackbird. A female (spar) weighs about twice as much and, at 250 – 300g, is about the same size as a collared dove.

There is a good evolutionary reason for this. If the two sexes are different sizes, they can specialise in hunting different sizes of prey. Thus muskets hunt small birds up to about the size of a thrush, while his bigger mate hunts larger prey up to the scale of a wood pigeon. This means they need to defend a much smaller territory from rival hawks.

A female goshawk can be twice the size of her mate (Lucy, pictured, is not her mate)

(Photo: author’s own) 

Goshawks are like an inflated version of the sparrowhawk. Males (tiercels) typically weigh about 750g (about the same size as a crow) and females might average 1.2 kg . Both sexes can be considerably bigger because following their extermination by gamekeepers in the 19th century, they were reintroduced by falconers – accidentally and deliberately - with imports from the Continent.

Now, some ornithologists have tried to argue that the dramatic recovery of wild goshawks over the past 60-odd years is a natural phenomenon. The science suggests otherwise. There are many goshawk subspecies around the northern hemisphere and thus the genetics of the released/lost birds vary wildly in size.  British goshawks are much bigger than their nearest subspecies in France, the Netherlands and Spain. This points strongly to a Scandinavian origin – and falconers have imported (and lost) hawks imported from Sweden and Germany for well over a century.

A six year-old male goshawk

(Photo: author’s own)

The last point I’d like to make about the true Accipiters is that you get a good idea of age from the irises of the birds. When newly hatched these are blue, by the time they fledge (around 10 – 12 weeks) these are light yellow. As time goes on, this deepens. I have two gosses at the moment – one, Owain, is six years old and has fairly dark yellow eyes. His hypothetical mate, Gwen, is 12 and has irises which verge on orange.

Gwen - 12 years old and full of volcanic ire . . 

(Photo: author’s own)