Monitoring breeding birds at Cabragh Wetlands

There is a small band of dedicated bird ringers who monitor the breeding birds at Cabragh Wetlands.

For the past sixteen years they have been running a Constant Effort ringing project. The project involves putting the same amount of netting, in the same places, for the same amount of time each year. Thus, any changes in the numbers trapped reflects the status of the population.

Ringing is a vital tool for bird conservation and the science of ornithology. It involves the trapping of wild birds and fitting them with a light metal ring. Each ring has a unique number and an address stamped on it. The bird is examined to establish details such as age, sex, weight, wing-length, moult and general body condition.

It is released as quickly as possible. This bird is now identifiable and if it is found alive or dead anywhere in the world, we can learn how long it lived, how it died, to where it migrated and so on.

The most commonly asked question is ' how do you catch them?'. Most song birds are trapped by mist nets. These are very fine black nets which are about 9 feet high and may be 60 feet long. When stretched between two bamboo poles and placed in front of a hedge, they are practically invisible. When the bird flies into a net, it falls into a pocket where it can't struggle and hurt itself.

A trained ringer will then extract it from the net and place it in a bag to reduce stress on the bird to a minimum. The smaller rings are made of pure aluminium. If the act of ringing a bird caused it to behave differently to other birds, then it would be a useless scientific tool because all results from ringed birds would be biased. The best indication that rings do not adversely affect birds is the fact that small birds such as Goldcrests can survive for years and even migrate to France and Spain showing no ill-effects. Larger birds such as Razorbills have lived for 50 years and have worn out three rings!

Resources for conservation are always scarce. Projects must be based on sound scientific data. If a species is in decline, there is either a problem with reproduction or with survival. For example, when the Peregrine population crashed in the 1960s, it was the thinning of egg-shell caused by poisons like DDT which were to blame. There was no evidence of reduced survival of adults. DDT was banned and the population recovered.

Recently, there has been a marked decline in Song Thrushes in Britain. It was found that Song Thrushes were producing as many eggs as ever, so the problem had to be survival. When ringing data was analysed they found that year-to-year adult survival was fairly constant. Year-to-year juvenile survival had decreased significantly.

By having this data available, conservation agencies were then able to target their resources more effectively at the problem of juvenile survival and the possible effects of slug-pellets on young Thrushes.

The constant effort ringing at Cabragh has shown that there is a steady decline in the Sedge Warbler population. The decline is seen in both adults and juveniles. This may be due to the condition of the reed beds and is something we are planning to address later this year.