‘The pungent odour of guano and the guttural calls of seabirds’.

This sounds like the typical description of a coastal breeding seabird colony. However, it can also be applied to the edge of a Cheshire woodland bordering Rostherne Mere National Nature Reserve, approximately 45km from the nearest sea.

Rostherne Mere plays host to one of the region’s largest inland breeding Great Cormorant (Phalacrocorax carbo) colonies, which has witnessed a rapid expansion in only a few years.

Cormorants have sporadically bred inland in Britain for centuries but a marked acceleration occurred from the early 1980s. By 2005, breeding had been noted at 58 inland sites with the breeding population rising to at least 2,096 pairs. This figure actually exceeded the coastal total of 1,564 pairs (Mitchell et al. 2004, Newson et al. 2007, Norman, 2008). Interestingly, a number of the early inland nesting sites appear to have undergone a population decline in recent years.

In Cheshire, Keith Massey reported on the ‘First Nesting of Cormorants in Cheshire and Wirral in 1999’ in The Cheshire and Wirral Bird Report 2000. The location was Fiddler’s Ferry Power Station but the two eggs laid disappeared without a trace. It was five years later before Cormorants successfully bred in Cheshire, and amazingly simultaneously at four locations – Frodsham Marsh, Fiddler’s Ferry, Trentabank Reservoir and Rostherne Mere (Norman, 2008).

At Rostherne Mere, nesting first occurred in 2004 with 5 nests recorded. The graph below shows the rapid increase in nest building in subsequent years, with an amazing 160 nests logged in 2011.

Cormorants have roosted in a series of alders at the foot of Harper’s Bank Wood at Rostherne Mere for many years but these numbers have gradually built up in recent times, peaking at 457 birds in May 2011. This count was augmented by many of the young birds of Rostherne origin. With between 2 and 3 young in each nest, that is a lot of fish suppers for the parents to provide. It is thought that many journeys are made to and from waterways around the county and possibly beyond.

The number of Cormorant nests at Rostherne Mere 2004 to 2011. The trend line represents a moving average.

Monthly maximum counts of Cormorants roosting at Rostherne Mere 1976 to 2011.

As in many other sites, the first nest builders at Rostherne appeared to show typical plumage characteristics of the race Phalacrocorax carbo sinensis, showing extensive white on throat and forecheeks with conspicuous white plumes in a solid stripe on sides of the nape. As the colony has developed it appears the subspecies Phalacocorax carbo carbo has possibly become the major breeder. However, separating the races is extremely difficult and inter-breeding has also been reported from other sites (Newson et al. 2007).

Interestingly, an examination of breeding performance has shown that inland breeders have a higher nestling survival rate than coastal birds and they tend to breed for a more protracted period (Newson et al.2005). At Rostherne Mere, the first nests are often visible in early February, supporting these findings.

After the chicks make their first tentative flights, they gather in large parties for fish catching practice. This can involve up to 60 birds which makes an incredible spectacle as they herd fish into the shallows. On occasion, the fish literally jump out of the water to avoid the predating pack.

As a final comment, a word of warning is required. After venturing slightly too close to the colony earlier this year during some scrub clearance work, I received the gift of the regurgitated head and guts of a large roach which descended from a great height. Others have said it was not intended but I’m not convinced!

 

References

Mitchell, P.I., Newton, S.F., Ratcliffe, N. & Dunn, T.E. (2004) Seabird populations of Britain and Ireland. T. & A.D. Poyser, London.

Newson, S.E., Marchant, J.H., Ekins, G.R. and Sellers R.M. (2007) The status of inland-breeding Great Cormorants in England. British Birds100: 289-99.

Newson, S.E., Hughes, B., Hearn, R. & Bregnballe, T. (2005) Breeding performance and timing of breeding of inland and coastal breeding Cormorants Phalacrocorax carbo In England and Wales, B.T.O., Bird Study,52,10-17

Norman, D. (2008) Birds in Cheshire and Wirral, A breeding and wintering atlas, Liverpool University Press, 162-163.