Finding Out About… Cormorants

Friends volunteer, popular guide and bird expert Trevor Gunton introduces the first in a series of informative articles written during lockdown and shared originally with our volunteers.

Image: Sunny, CC BY 2.0

There be Pelicans breeding at Paxton Pits!

Yes, its true, Cormorants are members of the Pelican family, Latin name Phalacrocorax.

Two sub-species breed in Europe and it is mainly the southern race, Sinensis that is found breeding inland, including the UK.  The other race is larger, named Carbo, is principally a seabird and breeds as far north as Iceland and northern Norway.

I first met Cormorants on the Yorkshire coast, where due to persecution by fishermen it has always been a rather scarce breeder, and its near relative the Shag has fared little better.

Here in the UK we have traditionally looked upon the Cormorant as a seabird, but across Europe this is not typical, with large inland populations of over one thousand nests in the flooded river systems of the Rhone, Danube and Rhine.

It is particularly numerous in The Netherlands, where the New Polders hold many thousand pairs, so is it possible that our first colonists of the modern age originated from here?

Historically Cormorants nested in trees in Norfolk during the Victorian period before they were shot out. The last record of Norfolk tree nester occurred in 1917.  This leads me to wonder if, back in pre-history, the Cormorant actually nested in many inland counties. This may have been before The Fens were drained and the man-made Norfolk Broads were created.

Image by Sunny, CC BY 2.0

Anyhow, to the hard facts:

Abberton Reservoir in Essex was first colonised in 1981, when 9 pairs nested. This, the first inland breeding colony grew rapidly to reach 150 pairs in 1986. The 500 mark was soon reached before dropping back to around 250 pairs in 2016.

Paxton Pits was England’s second inland site. I found the first nest in 1988(which failed), but the following year 9 pairs nested successfully. Our colony reached 218 pairs in 1996, dropping back to about 180 pairs in 2005 and more like 50/60 pairs in recent years.

The average number of young raised per nest seems to be about 2.5 per nest (how do you count half a Cormorant?)

Winter roosts have been of great interest to me over the years and it is thought that many of our birds leave the colony in the Autumn, to be replaced by birds from other sites- mainly from UK colonies, but a few from near Europe. From a max count of 131 birds in 1987, to a steady increase to 880, and then during the very hard Winter of 1994, we counted an all time high of 1,153 birds on Jan 4th. This really was an amazing site, as we seem to have attracted Cormorants from all over East Anglia!

Recent counts have averaged from 100-200 birds. So, over the years Paxton has mirrored Abberton in that both original sites have shown an increase at a similar rate. So, what seems to be happening is that some birds break away to form new colonies; and today the original sites have become 35, hosting some 1,330 pairs in England alone.

Image by Pete Beard, CC BY 2.0

Away from Paxton, Cambridgeshire has 4-5 other nest sites, including a well known one on The Ouse Washes. Jim, our former Head Ranger told me, some years ago, that, at Grafham, larger fish were being introduce making it more difficult for Cormorants to feed. Is this the cause of the decline of the Paxton colony? Another unproven puzzle.

One very unusual nest site is on The Inner Solway Firth, between England and Scotland, where after WW2, Cormorants nested on an old RAF bombing target! This four-legged wooden platform at one stage held 66 nests, now down to just 20 pairs in 2019.  This is due to the deterioration of the structure.

In Victorian Britain, many bird species were eaten, including the Cormorant. I have found the following recipe: Place the Cormorant in the ground for 2/3 days. Then dig up the bird and remove all the entrails before replacing them with a Portuguese onion! Cook slowly and when tender, carve like a goose or duck. Anyone fancy giving it a try?

As you read this, many of our Cormorants will have departed for The Wash, Mersey and other sites.  Some big juveniles will be around the trees, looking just like Ospreys (as one birdwatcher remarked to me). Many birds will replace them, making an amazing sight as they return to the trees on Heronry South at dusk.

So, as you can guess, I have a long-standing relationship with Cormorants over 40 odd years.  I hope that the dark fisherman of Paxton Pits will remain a very special feature of our wonderful reserve for many years to come.