It is one of natureâ€™s cruellest tricks: a tiny bird struggles to feed a large cuckoo believing it is her own.
These incredible images of a reed warbler feeding a baby cuckoo were taken at Slimbridge Wetland Centre.
Cuckoos lay their eggs in other birdâ€™s nests fooling them into believing it is one of their young.
The baby cuckoo, which has a seemingly insatiable appetite, hatches first and then quickly disposes of any competition by kicking any other eggs out of the nest.
Cuckoos are on the decline in the UK so when two pairs of parents arrived at Slimbridge earlier this year staff were hopeful that they would produce some young.
James Lees, the reserve warden who took the photos, said: â€śI felt very excited when I saw it as I had never seen a baby cuckoo and it was amazing to see the two parents flying around desperately trying to provide it with enough food.
â€śThere was quite a crowd of visitors watching it as it was happening right next to our main playground Welly boot land.
â€śA cuckoo is about the size of a dove, so it would weigh about five times more than a reed warbler.Â They also take twice as long to fledge as a warbler, so these poor parents are stuck feeding them for longer.â€ť
The cuckoo is likely to remain for a few days.Â Check our daily wildlife sightings for the latest news: http://www.wwt.org.uk/visit-us/slimbridge/wildlife-sightings