Kingfishers: are they getting commoner or rarer?

People often say that Kingfishers are becoming commoner, or recovering, and that they are a sign of the condition of rivers and other freshwaters.

Indeed, I heard an important person say just this earlier in the week, perhaps because it had been in the papers recently, that Kingfishers were increasing. And someone else was quoted as saying that increased Kingfisher sightings on canals was a ‘…testament to the huge improvements in water quality…‘.

Even the BBC falls for this stuff.

Is any of this true?

Sadly probably not.

As I’ve already written recently, improvements in rivers over the last 10 years are now occurring ‘at a snails pace’ or in the slightly less graphic language of Defra statisticians: ‘there has been little recent change [in river quality]’. So not much to affect Kingfisher numbers there then.

And as for the birds themselves, the pretty reliable and well-organised British Trust for Ornithology Breeding Bird Survey shows there has been no change in the number of Kingfishers since the mid-1990s. This is the same survey, believed by most serious people, that shows Turtle Doves have declined by 70% since 1995, Swifts by 19% and Yellow Wagtails by 52%, while Woodpigeons have gone up 35% – all changes which are statistically reliable – indeed, so reliable even the Government uses these data.

Looking back a bit further, the BTO Waterways Bird Survey, which ran from 1974 to 2007 showed that Kingfishers dropped in the mid 1980s and then recovered to exactly the same place by the mid-1990s. Nobody seems to know exactly what caused this, although there is a good match with the weather (see the graph below), with cold winters in the 1980s coinciding with the decline of Kingfishers, and warmer winters coinciding with the recovery of Kingfishers.

The graph shows the average January temperature in Oxford for 5 year periods compared to the population index for Kingfishers. The temperature pattern matches pretty well with the number of Kingfishers

But of course this doesn’t prove that the changes in Kingfishers was due to the weather. Could water pollution also be having an effect? This is more difficult to tell: as far as I know nobody has ever analysed the relationship between Kingfishers and river quality – despite the repeated assertion that they are connected. When you do, there’s a problem because it’s hard to find water quality data from the 1970s; although it exists, none of it is in modern electronic archives.

So although it’s possible to quickly knock-up graphs from Defra archives, like the one below, going back to 1980, this doesn’t tell you what water quality was like before the Kingfisher started to decline in the early 1980s. You could conclude that Kingfisher numbers have steadily climbed alongside water quality improvements.

Average river oxygen levels have increased since the 1980s - at the same time as the Kingfisher recovery - but crucially we don't know what they were when Kingfishers declined in the 1970s. Chances are, oxygen levels were even lower then.

But it seems implausible that water quality was good at the beginning of the 1970s, suddenly declined enough to affect Kingfishers, and then in 1980s started to get better again. Indeed reports by Terry Langford and colleagues on the history of mid-20th century river monitoring, a time now passing into history tend to confirm this. At least in the bigger rivers impacted by towns and industry, water quality in the 1970s was worse than in the 1980s. Although someone needs to look at this more carefully to be certain, it looks like that 1970s decline in Kingfishers was in fact associated with the cold winters, not pollution.

Across the country as a whole the best information we have at present is that numbers of Kingfishers overall haven’t changed since the 1970s – that is, getting on for half a lifetime. Now it’s entirely possible that in individual places numbers of Kingfishers have gone up and down a bit. But the pattern since the BTO started monitoring is ‘fluctuating with no long-term trend‘.

Worth remembering the next time someone tells you that the increase in Kingfishers is a sign of improvement in rivers.


2 Responses to “Kingfishers: are they getting commoner or rarer?”

  1. LIZ MacGillivray Says:

    Hi, read with interest recent post on kingfishers. We stay for six monthts of the year on our narrowboat and have been constantly surprised at the numerous sightings of these remarkable birds. Presently we have a mooring at Brentford on the Paddington Arm of the Grand Union Canal and just next to the Thames Gaughing Lock. We have a pair of kingfishers nesting close to the boat and are delighted many a morning to have one of them perching on our front rope. Beautiful start to anyone’s day.

  2. neil Says:

    Interesting post. I read your post on Salmon too. I often wonder how we can be improving on these things and yet much of our wildlife seems to be decline.

    PS Been wandering through the old posts and some great stuff there 🙂

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