The arrival of the cuckoos at this time of the year is always welcomed as a symbol of spring.

Their distinctive and easily recognisable calls will be heard in parts of Oxfordshire as they move around preparing for the nesting period They waste little or no time settling down to business.

Their day begins early. In recent years, cuckoos were usually the first birds to be listed by people attending the annual dawn chorus counts starting at 4am at St Mary’s Fields, near Kidlington.

The birds there are in the thick bushes from which sound out not only the well-known calls but also surprising bubbling notes, presumably mostly coming from the females.

After this brief display, they fly swiftly off along the Cherwell valley seeking nests of potential hosts in which to deposit their eggs.

Our knowledge of cuckoos has been considerably increased by the efforts of Oxford birdwatcher Mike Bayliss.

For more than 25 years he has surveyed their activities along the Thames from Wolvercote to Radley. As a result he has become a noted authority, including being involved in making television programmes on the subject.

One extraordinary find was of a female cuckoo that returned to the Trap Grounds, in Oxford, and laid eggs every year from 1983 until 1999. This is a joint European record. Recently, Mike has noticed a steady decline in their numbers.

Last year was of great concern because, although adults returned, no young birds were found along his study area.

The reason is not clear.

Possibly the absence of caterpillars and insects following a period of difficult weather conditions may have prevented females from producing eggs. The situation will be carefully monitored this year in the hope this is not a future trend.

When they have finished depositing their eggs the adults do not stand on ceremony but move away immediately.

Later, when the young birds hatch, they have to build their strength for the lonely journey ahead, so they spend their time yelling for food. Barry Hudson’s photograph, right, shows what they look like.

If would be useful to know if you see any young cuckoos this summer.