Great thread, really enjoyed it all. Waterlow Park was a favourite childhood haunt and the Heath was very much my patch in later youth. The couple of times I actually got up and went out early were always when the good birds were seen. In those days (early nineties) LSW was still relatively common on the Heath, even had one in the garden a couple of times. Disappearing ducklings I would certainly put down to Pike, precisely no Mallards used ever to fledge from the Boating Pond, pike would have the lot. You'd just see a swirl and the last duckling in line would disappear. Terrapins however are voracious sods and if hungry could I am sure chomp a small bird if so inclined. As for rats the Park, I recall them as being easily the biggest and boldest that I have ever seen, anywhere. Like small dogs indeed. I remember my sister filming something Absurdist once in Waterlow for her film course, for which the one prop was a banana. They had a bunch and one plastic one 'in case of emergency'. Each time they placed a banana on a bench and retreated a few yards to the camera, this great big rat jumped out from the shrubbery, grabbed the nana and beat it. This happened one by one to the whole bunch until just the plastic one remained. Naturally it was stolen by the rat before they could get their shot.
Shame I missed that Bittern, I do love a London twitch as it takes me back to my bird-saturated teens. The Alpine Swift on the Heath a few years back was utterly glorious, well work the schlep up from Brighton. Maybe you will chance upon something equally pulse-quickening in your pre-work forays. Keep up the good work! Cheers, Tim