Cliffe pools in Kent is managed by the RSPB, it consists of saline lagoons and pools created by clay diggings before it was taken over by the charity in 2001. It is well situated on the isle of Grain in the Thames estuary as a hot-spot for migrating birds as they head north or south. John and I had visited this reserve quite a few years ago in spring and rather than go to one of our usual haunts I thought it would be nice to give it another go.

To be brutally honest the landscape that Cliffe pools is set in is downright ugly, depressing and a bit grimy. Unlike nearby Elmley this reserve is not natural marshland, it is a reformed brownfield site surrounded by the rusting relics of a more prosperous industrial age. Container cranes stand like giant giraffes on the horizon, waiting to serve hulking iron ships full of imports, outlet pipes encrusted with guano stick out over the brown water of the Thames and the footpaths are lined with scraggly ivy and dog crap.

Birding really does take one to interesting places, some stunning and some not so much, but for the birds themselves it is all about whether the habitat provides them with what they need – and on migration that means food. The mud of the Thames estuary is literally swarming with invertebrates, which is why it is so important for waterbirds – but at high tide when all the mudflats are covered by the sea the birds have to find somewhere on land to feed and wait for the water to recede – which is where Cliffe pools comes in.

The first lagoon John and I saw as we walked onto the reserve stank like putrid 100-year old herring that had been mashed with rotten seaweed and garnished with decaying skunks. Fortunately birds don’t have much of a sense of smell and we counted 45 Little Egrets on this pool alone, these were standing along the shore but on the water sat a very many Great Crested and Little Grebes as well as vast numbers of Coot.

Along at the next pool were large numbers of eclipse-plumage duck, mostly consisting of Mallard, Tufted Duck and Pochard – it was pleasing to see so many of the latter as this is a species that is not fairing well. Our first waders were the ubiquitous Redshank, flashing their wing-bars and piping away as they do, it was around now John spotted a male Marsh Harrier swooping far-away over the pools; its grey, black and brown plumage being striking even from a distance.

The next pool provided us with a lot of interest and kept us busy for a while, for half-way out there was a low island with muddy edges that had attracted a lot of waders. Five Avocets made everyone else look dirty, some uncharacteristically showy Snipe were sleeping or probing the mud, a lone Green Sandpiper strode along the shore and a few smart Ruff showed off their butterscotch plumage. A handful of Black-tailed Godwits stood out due to their size but otherwise were dull in their brown winter coats – later on we saw flocks of hundreds roosting on the mud.

We then managed to pick out a couple of smaller waders that at first glance looked like Dunlin but after consulting the field guide and noting the buff breast, elegant profile, uniform brown upperparts and de-curved bill we decided were in fact Curlew Sandpipers – a delightful bird that is altogether much scarcer than Dunlin. As a Cetti’s warbler chattered out a brief ditty a group of pale waders shot over the pool on knife-edged wings and alighted on the shore – the overall pale plumage, slightly up-curved bill and long, green legs confirmed one of them was a Greenshank. The others were actually ordinary Dunlin.

Now the most exciting bit of the day took place – John declared he had seen a tern flying around at the far back of the pool but it was flying fast and had gone out of view, at this time of year and in this location there are a few likely tern species – including some quite scarce ones. The bird reappeared and I got onto it with my bins, it was definitely a tern but the plain grey upperparts, black hood and black bill ruled out Common or Arctic – leaving exciting possibilities. I hurriedly checked the book and watched the bird for key features – despite the distance it was clearly a Black Tern – a scarce passage bird that no longer breeds in this country and it was the first I had ever seen.

We decided to head up to a look-out point where other birders were positioned as it gave good views over many of the pools and we hoped for a closer view of the tern. It was a great view from which several pools could be seen well, the Black Tern was hawking over the nearest one and for the next hour or so we had good close views as it snatched insects over the surface of the water. There was plenty else to see from there though too; a pair of small plovers were feeding together in a muddy creek, at first I assumed they were both Ringed Plovers but one didn’t look right and after checking the book it turned out one was a common Ringed Plover and the other was the scarcer Little-ringed Plover – giving a nice side-by-side comparison of these similar birds.

We then noticed a small, pale wader feeding alongside the plovers, it was smaller than them (and they are not very big) and superficially looked like a Dunlin, but the very small stubby bill, the plumage colour, white stripes on the upperparts and the tiny size gave it away as a Little Stint – only the second I have seen and by far the best view. The next surprise came in the form of a Water Rail, I spotted one quite boldly pottering about on a mud spit in full view, most unusual for this highly secretive species – we had good views for a few minutes before it slunk back into the reeds.

The obliging Water Rail.

That viewpoint was the highlight of the trip, but as we walked around we saw other great birds too – Sand Martins and Swallows fluttering under the heavy grey clouds, a Sandwich Tern hiding among some Common Gulls on a rusty railing, Kestrels quivering over the fields, Curlew flying over and a lone Golden Plover wearing his spangly coat. One of the best bits though was watching a huge flock of over 300 Avocets rise into the air and pass over us – every wingbeat making an audible whooshing sound, the whole flock flowing like a silk sheet in a breeze – the whole sight a piece of art with their black and white plumage flashing in the sky.