The sound of a cuckoo is probably the most recognised bird song in the country and it has been a delight to hear one calling over our reed bed in the last few days.
While us humans love hearing the two syllable call, the sound strikes fear into the smaller birds nesting on our reserve. This is because the cuckoo is a brood parasite, which tricks other birds into raising its young. At Martin Mere the most frequent bird to be conned by the cuckoo is the reed warbler.
The reed warblers and other birds are well aware of the cuckoo’s parasitic habits and, if you see a cuckoo flying over the reserve, you will probably see it being attacked by smaller birds trying to drive it away. However, when a cuckoo finds a suitable nest it will lay an egg alongside the host species’ eggs. Once the cuckoo chick hatches out, it then goes about emptying the nest of the host species eggs to ensure that it has the sole attention of its unwitting host parents.
With only one mouth being fed by the host parents, the cuckoo soon outgrows the nest, as it is twice as big as the parents themselves. However, the cuckoo will still be fed outside of the nest for quite some time. A great example of this happened at Martin Mere in 2020, when a young cuckoo took up residence for almost a week outside our Gordon Taylor Hide. This provided some great photo opportunities for many visitors, as a pair of reed warblers shuttled to and fro to feed their over-sized, imposter offspring.
Once fledged, the cuckoo will start its migration south. A British Trust for Ornithology tracking project has seen cuckoos fitted with satellite tags for the last ten years and this has shown that British-born cuckoos head for an area around the Congo Basin.
At the end of April, the project recorded PJ, a cuckoo fitted with a satellite tag back in 2016, returning to his breeding grounds in Suffolk for his seventh summer. PJ had started his journey north from the Congo in late February, made a non-stop Sahara crossing on the 4th April and arrived in Spain a few days later. By the 24 April PJ was back on his territory in Suffolk.
Our Martin Mere cuckoos will have made similar journeys, such is the attraction to have your kids raised by somebody else.