This summer I filmed a pair of reed warblers run themselves ragged raising a cuckoo chick almost five times their size. These small, delicate birds had been tricked into thinking the cuckoo was theirs. It’s an ancient parasitic relationship that has long fascinated me.
In fact, my film was a long time in the making. I first attempted it at a nest I found close to my home and gallery here in East Yorkshire some 30 years ago. But back then my equipment was relatively basic, as were my filming skills, and I have hankered to try again ever since.
Cuckoos in decline
These days, however, cuckoos are more scarce. Recent dramatic declines in populations mean they are now listed as ‘red list species’, signifying their conservation is of highest concern, and I for one can confirm they are much harder to find. Each year I visit the same set of lakes to film kingfishers, swans and grebes that live on this species-rich body of water and in the spring, I used to hear the distinctive ‘cuck-oo, cuck-oo’ calls of the males, which gives this species its name.
But it’s a sound I hear less and less these days and, for a few years, not at all. Then last year, after a long absence, I heard three. Two males calling ‘cuck-coo’ and a female’s a strange, squeaky response. Female cuckoos have perfected the ability to produce almost perfect replicas of their hosts’ natural eggs over generations, and different birds will attach themselves to different species. This is how they trick the host species to incubate their eggs for them. At these lakes, the cuckoos were specialists in reed warbler eggs.
Searching for cuckoos
That year I spent days checking reed warbler nests for evidence of their eggs or chicks, carefully walking through reed beds and peering gently into their neat cup-shaped nests. Wading through chest-high freezing cold water, I found a total of 15 reed warbler nests, but no cuckoo eggs or chicks. Then again, this spring my heart leaped when I heard my first male cuckoo call but sank just as quickly when there was no answering sound from a female.
Cuckoos migrate from Africa each year to breed and, since it takes two to tango, I kept an ear out for a reply. But after a few days the calls grew more and more distant and I assumed the male had travelled down a nearby canal, presumably searching for a mate there. I decided to check for signs all the same and, again wading waist-deep through the reed beds, discovered a total of 13 reed warbler nests, but again none had cuckoo eggs inside.
Reed warbler hosts
One of the warbler nests was still under construction and was close to a hide I had built to watch swans from. It was fascinating watching the warbler pair busily building and, intrigued, I paused my swan watch to film the process as they went on to raise their chicks.
But as these young warblers fledged, I decided to resume my quest to find a cuckoo and to re-check all 13 warbler nests once more. I wasn’t particularly hopeful this time, I had visited the reed bed almost every day for months whilst filming both the swans and the nesting reed warblers and hadn’t so much as heard a cuckoo.
Still, wading through water up to my waist, I set off for one more round. There was one area of the reed bed I hadn’t been to for almost three weeks and the last time the water here reached over the top of my chest waders. This time I entered the lake from an island and slipped carefully down. Before I had waded a couple of metres, I spotted a warbler nest I hadn’t seen before. It hung, suspended between the reeds.
Finding a cuckoo chick
Reluctant to get too close, I reached over with my mobile phone and photographed the nest, hoping to snap a cuckoo egg. A cuckoo egg is only slightly bigger than a reed warbler’s and is perfectly matched in colour.
As I brought my phone back to take a look, I couldn’t believe what I saw. Instead of an egg, I had photographed a cuckoo chick, so big it almost filled the nest. About 10 days old and dark in colour, its gun-metal grey pin feathers were already showing white tips, where its flight feathers were due to come through. Cuckoo chicks roll all their host’s natural eggs out of the nest as soon as they hatch. This one had already kicked out the competition and was now the sole nest occupant – gobbling up all the food the warblers brought.
Building a hide
I wasted no time moving my hide from where I had been photographing the first set of warblers. It was only 50m away but in deep water and working alone, this was hard work. One by one I slowly brought each section of scaffolding to its new location, pausing each time the warblers arrived at the nest so as not to disturb them.
Once I had transported all the sections of my hide to the nest, I heard a warbler call. I stepped back a bit, standing still as the warblers fed their hungry imposter just and arm’s length away. The first time I filmed this secretive process, I had found a total of eight cuckoo chicks and although I managed to film one, almost all the others drowned after a big storm hit and pulled apart the fragile warbler nests. I didn’t want this to happen again, so I waited until the reed warblers left and then carefully tied the reeds beneath the nest together to give it extra support.
Filming the reed warblers
By night fall my hide was complete and I was holed up inside it early the next morning, eager to begin filming. I had yet to set up my cameras when both warbler parents arrived, their beaks stuffed with insects. Again, I stayed still as the warblers fed the chick, barely paying me a second glance.
The height of the nest meant it was difficult to film at eye-level, so I set up a remote camera above the nest as well as four other cameras at varying angles to catch the comings and goings of these birds. Then, as the cameras rolled, a warbler arrived with a mouthful of insects and I filmed as it gently proffered them to the chick.
I watched fascinated as further food deliveries arrived. Whenever the warblers approached, the cuckoo chick’s red gape opened wide, and it let out a shrill call for food. The sound reverberated, deliberately designed to sound like a whole clutch of warbler chicks and encourage the warblers to find more food.
Fostering duties
After each feed the adults perched on the edge of the nest, peering inside as they waited for the cuckoo chick to poop – after all what goes in must come out. A cuckoo poops into of a faecal sack which the warblers carry away from the nest and drop into the water. This is normal behaviour for small birds since keeping their nests clean is imperative for the survival of their chicks.
I visited the nest every day to document the cuckoo’s development - even on days when I was beginning to feel exhausted at the prospect of yet more hours spent with my feet in the cold water. I had, after all, already spent months watching swans, kingfishers and the first warbler nest.
Cuckoo chick growth
Over the weeks, a wide range of insects were delivered. Many I didn’t recognise, or the action was too fast to see, but I did spot mayflies, hoverflies and even damsel flies. It wasn’t long before the cuckoo chick was so big it struggled to fit into the nest and its wings flopped over the sides. I watched as it tried tucking them back in, but they soon flopped out again as it preened or was fed.
Day by day, I monitored its changes. Its feathers grew through their steely sheaths of the pin feathers, all dark grey and chocolate brown fringed with white tip. And all the while the food kept coming and the chick kept growing. The warblers were very attentive parents, devoting all their time and energy to this imposter.
They regularly checked its feathers, making sure it was nice and clean and pecking over spilled food like any fussy parent. And they were always neat and tidy, carrying away any loose nesting material as soon as they spotted it.
Exhausted reed warblers
And as the cuckoo got bigger, its calls for food became more frantic and louder, driving the warblers to work even harder. Once, after the warblers had fed the chick, it lashed out at the nearest warbler like a demanding teenager, pecking at the warbler to encourage it to bring even more food.
After so long watching this cuckoo, I noticed it would only call out once it spotted a warbler approach. This tactic ensures chicks don’t attract predators, although as this chick got older the sound grew louder, and I often heard it as I was carrying my camera equipment to the hide and was still some distance away.
Cuckoo fledge
This made me anxious since there were sparrowhawks, tawny owls, crows and buzzards in the area and so it was always a relief to reach the hide and find all was well.
Soon the chick was venturing to the rim of the nest. Then one day, as the wind blew through the reeds, I noticed the cuckoo chick peering out over the nest. It made a new sound; a sharp cheep that stood out from its usual reverberating calls and is a call designed to help the parent birds follow and continue to bring food after fledging.
The following morning, the cuckoo wasn’t in the nest. I soon found it in a moorhen’s nest at water level. Luckily it was there and not in the water and thankfully the moorhens had finished using the nest – an adult moorhen is territorial and would have killed this intruder.
I pointed my cameras down at this lower level. The chick looked much happier here where it was no longer rocked by the wind. It was great to see that the warblers were bringing food to this new location. Although still unable to fly, the fledgling was much more adventurous and I watched as it ran from one side of the nest to the other, jumping onto reeds before hopping back onto the nest.
As the evening came, I grew worried about its safety down there where predators could easily find it, so I popped it back onto the warbler nest. With cuckoo populations so low, I felt compelled to do what I could to help this one survive.
But the next morning it had hopped back out. Again, I found it low down in the reeds, this time on a small willow branch just above the water where the adults were still busy feeding it. The cuckoo perched there for hours, gobbling up food delivery after food delivery. But then it made a jump for dry land and scrambled up to the island. I was pleased it had made it there as many cuckoo chicks drown during their first days out of the nest and the weather had been particularly wet and windy
Once on the island, the cuckoo started hopping up through the willow branches and when it was a few feet off the ground it settled and cheeped again for food. The warblers found it straight away and again began to deliver more food. Then the cuckoo chick made its way onto a broken-off stump and here the warblers had nothing to perch on to feed it.
I watched intrigued as one hovered in front of the cuckoo trying to stuff the insects into its beak and then another landed on its back and reached over its head that way to feed it. In this position you could really see the size difference between the cuckoo chick and the tiny warblers.
Gaining flight skills
Over the next days the cuckoo fledgling stayed on this island, practising its flying skills. It soon progressed from short jumps between branches to longer flights of a few metres. All the time the warblers brought a seemingly everlasting supply of insects.
Once after attempting a longer flight, the chick crash landed into the reed bed and slipped into the water. Again, cuckoos are in sharp decline so I helped it back to dry land and soon its flights got stronger and it left the island, flying well.
Watching its halting, first attempts, I was amazed to think that in a few weeks, this bird would soon set off for an epic journey to West Africa, but that’s the magic of nature. And what an amazing experience it was to document this part of its life.
