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Disappearing Cuckoos

In recent years though we have seen headlines like these:

Bbc -are -cuckoos -disappearing

Cuckoos are disappearing fast. How many more ecological warnings do we need?

Britain’s cuckoo population plummets by a fifth in one year

Are cuckoos disappearing from the UK?

This is what the science tells us:

The British Trust for Ornithology (BTO) coordinates the work of thousands of volunteers who carry out a wide range of studies on the distribution and breeding success of British birds. Data from two of their most important surveys, the Common Bird Census (CBC) which ran from 1962 – 2000 and its successor the Breeding Bird Survey (BBS), have shown a calamitous decline in the number of cuckoos in our countryside. By 2014 there were only about a quarter of the number of cuckoos being recorded compared to the 1970’s and 1980’s.

Cbc -bbs -england -1966-2014-cuckoo

Every twenty years or so the BTO joins forces with Birdwatch Ireland and the Scottish Ornithologists’ Club to produce a Bird Atlas for the whole of the UK and Ireland. The field work for these atlases is on a massive scale and involves three or four years of hard work by thousands of volunteers (over 40,000 for the latest atlas published in 2013). A comparison of the distribution of Cuckoos between the last two atlases (1988-91 and 2007-11) show that in much of England and Wales the Cuckoo has declined strongly. The Cuckoo is no longer an everyday part of British country life. Indeed if the current rate of decline continues then children growing up today may never hear a cuckoo.

Why are they declining? The reasons why Cuckoos have declined are complex and only partially understood. Research has concentrated on four areas:

  • A decline in the availability of insect food for the adults. Cuckoos are known to favour hairy caterpillars such as the Woolly Bear the caterpillar of the Garden Tiger moth. Populations of this moth have declined by about 92% since 1968 especially in the south and east of the country.
  • Declines in host populations. The Meadow Pipit, one of the commonest host species for the Cuckoo, is known to have declined by about 50% since the 1970’s. The Dunnock, one of the other main hosts, showed a similar decline in the 1980’s but has been recovering recently. The Pied Wagtail has remained fairly stable whilst the fourth main host, the Reed Warbler has increased.
  • Changes in the timing of breeding are also possibly important. Successful breeding of cuckoos depends on their host species having nests with eggs available to the cuckoos as they return from their migration. It is known that several species of bird in the UK are now breeding earlier because of climate change and Dunnock, Pied Wagtail and Reed Warbler are all laying eggs about a week earlier. Dunnock and Pied Wagtail nest early so it could be that fewer of their nests are available for returning Cuckoos to lay their eggs in, but as Reed warblers nest later then more of their nests could now be ready when the Cuckoos come back.
  • The fourth possible factor is to do with the migration route of Cuckoos. You can follow the migration of satellite tagged Cuckoos on the BTO website. Their route takes them from the UK across Europe and then across the Mediterranean via Italy, Greece or Sardinia/Corsica and then across the Sahara to their wintering grounds in West Africa. They return along a more westerly route, through Spain reaching the UK generally some-time in April. There are dangers all along this route. A lot of birds pass through the area where Italy, Germany and France meet and in 2015 this area was hit by a severe drought which may have reduced the amount of food available to the Cuckoos as they try and build up body reserves for the flight across the Mediterranean and Sahara.  There is on-going concern about illegal trapping of migratory birds along the Mediterranean coast and crossing the Sahara adds another level of danger to their migration. And then they have to go through it all on the way back to the UK in spring. Perhaps we should be amazed that any of them survive at all.

It’s very likely that each of these factors has some role to play in the declining fortunes of the Cuckoo. What is really sad is that we may lose the Cuckoo as a harbinger of Spring and that future generations of children may never get a chance to hear a Cuckoo.