Female sparrowhawk in the garden, 2017

Dear Readers, I am an avid reader of British Birds magazine, so I was fascinated to see an article about sparrowhawks in this month’s issue. A study of sparrowhawks in Edinburgh has shown that the prey taken by these predatory birds has changed over the past thirty years, in line with changes in the garden bird population. Sparrowhawks take more wood pigeons, feral pigeons and (gulp) magpies (I’d have thought it would be an ambitious ‘sprawk’ that took on a magpie, but there we go). These are all birds whose populations are increasing, in part due to supplementary feeding by humans. Sparrowhawks take fewer starlings, greenfinches and chaffinches, all of which have declining populations. This has led to an increase in the number of sparrowhawk eggs laid per clutch of one egg, which probably indicates that the females are well-fed, but this doesn’t translate into additional surviving nestlings: feeding an additional hungry mouth may put too much pressure on the parent birds. I did wonder if there’s a ‘chicken and egg’ thing going on here (sorry) – only the larger females are able to take on a bird the size of a wood pigeon, so maybe nature is favouring birds that are bigger, who are in turn able to take larger prey. At any rate, it’s good to see that sparrowhawks are so adaptable – having one in the garden is the North London equivalent of hosting a tiger, so, sad as it is for the victim, it’s always good to see one.

Lesser Spotted Woodpecker – from the Crossley Guide

The second article that caught my attention was about one of our rarest forest birds, the Lesser Spotted Woodpecker. This is a fiendishly difficult bird to locate, and has been something of a conundrum to conservationists: if you can’t find the birds, how can you get an idea about numbers, and whether their populations are stable, declining or even growing? This is where passive acoustic monitoring comes in. In the blogpost linked above, I mention the Woodpecker Network, a group of dedicated volunteers who have collected data on the bird since 2015. This year, they used recording devices which were placed in known Lesser Spotted Woodpecker territories and left to record for 5 days at each site. Then, each memory card was lovingly analysed manually – the spectrograms from the cards, plus the sound, would show a distinct pattern for each time the woodpecker drummed.

This was far from a straightforward exercise. The birds are most active in March and April, but this is of course a windy, wet time of year, and ‘weather noise’ can completely obscure the drumming sounds. Plus, LSWs drum very early in the morning, at the height of the dawn chorus. It was clear that the researchers needed something to help them, so they ‘trained’ some software to pick out anomalous sounds, using our old friend the Xeno Canto website. This has over 1100 ‘foreground’ recordings of the bird, and 478 ‘background’ recordings at last count, and so it provides a rich and varied selection of drumming sounds for the software to learn. By the end of the ‘training’ it was 95 percent accurate in identifying sounds, and picked up over 90 percent of the LSW sounds.

But what does it sound like? Have a listen below…

This is a French LSW, recorded by Stanislas Wroza….

And here is a rather closer Swedish LSW recorded by Lars Edenius….

And finally, here’s one from the UK by Jason Anderson, recorded in Burley, Hampshire

Anyhow, after all the recordings were analysed, it’s clear that the LSW is probably more widespread in Hampshire, Sussex and Somerset than was previously realised, and they were detected at sites where they hadn’t been observed for many years. This may mean that the population of the bird is better than was thought, but further investigation is needed: the authors of the report suggest a wider survey, to include a number of woodland sites where LSWs haven’t been recorded recently. They also point out that the devices could be used to detect other birds that are difficult to observe, including the Hawfinch, a notoriously tricky bird and another Red List species.

All in all, this sounds like an excellent way of gathering data on elusive species, with the minimum of disturbance. My only concern would be people stealing the recorders, otherwise I’d see if we could put one in Coldfall Wood. When we did our last bird survey, a Lesser Spotted Woodpecker was detected, but as far as I know, no one has heard them since. Or have we simply not known what to look for? There is always much more going on than we notice.