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sampling gaps20th May 2019Sampling gaps
Those who dip into this blog will know that I am concerned about data quality and sampling issues. These may seem arcane, but they do matter. After all, if big decisions (e.g. planning and allied topics) are decided on the science (yes, that would be nice, wouldn't it) to some degree, then it behooves us to provide the best data possible. After all, that way there is no hiding behind poor data; a political decision is just that, otherwise weasel words/ ways can prevail.
Why am I looking at this? It comes back to my interest in nightingales. They are very much on the slide: a few here and there seems more the case than the threes, fours and more of a decade or two ago.
My own sampling patch is up and down. 9 years ago I was awoken by nightingales. Those particular territories fell away. This year, on a quiet lull in the traffic, I can hear them from the garden from the same basic area as management has made this suitable once more.
The simple question is when should I got out to hear them? As the key is the singing male, then you have to get them on display. Once the brood is done and dusted,and hatched, the chances of detection fall dramatically.
Gilbert et al give the following advice: 1. at least 2 (preferably 4 ) visits in May 2. visits about a week apart 3. between midnight and dawn, or (thankfully for those of us that have a rotten metabolism that abhors such times) in the first 4-5 hours of daylight. That may well still mean 3.30-8am....
So far so good. As part of an assessment of when nightingales arrive I did my first couple of visits in April. The first one was heard in mid month. On the last day of April there were 3 detected. The first week of May turned up nothing, but subsequent weeks have had birds.
Plain sailing? Not really. The noisiest bird- and the one I hear from home- was first detected almost a month after the first. It then went quiet for 2 weeks. Late or early, it made no difference. Last week it was there one night, but silent the next. The next night it was there. The next it wasn't. In the fog of early morning it was there again, and counter calling too.
The lesson seems to be not to pin all of your hopes on a couple of visits, and certainly not slacken after a month or so. It seems that birds have a way of confusing the hopeful. So, it is 2 visits you are relying on (as in many EIAs) then you get what you deserve, and that probably won't be a nightingale. |
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