Friday, December 1, 2023

Breeding Hen Survey report 2022 – Mark Avery

I’m an enormous fan of the Breeding Hen Survey – I describe it and touch upon it in Chapter 2 of Reflections. I’m additionally a participant however even when I weren’t then I’d be poring over the annual report as quickly as I might annually. And so I had my first have a look at the latest report when it turned obtainable on line yesterday.

Many readers of this weblog would get pleasure from giving it the as soon as over too. It’s a mannequin of readability, of condensing many knowledge into sense and it’s typically well-written and appears good.

You’ll discover your individual explicit factors of curiosity, however listed here are three of mine, though I’m inquisitive about all of it.

1. Participation web page 7  Numbers of squares surveyed  besides backside line is variety of contributors.

These are simply the newest 16 years of the BBS (which began in 1994) they usually present a transparent (and anticipated) impression of covid on participation. Issues picked up in 2021 however didn’t recapture the degrees of pre-covid, nor did they in 2022. I’ve been a part of the underside row of numbers, contributors, for all of this portion of the scheme and again just a few years, and I’ve coated two squares in most years (together with in 2020) however final 12 months I simply didn’t discover the time to do one in all my squares (by way of a mixture of unhealthy climate, different commitments (work and play) and easily operating out of obtainable dates). And this 12 months the identical has occurred so I’ve admitted to my wonderful regional organiser that I’ll simply do one BBS sq. in future.

2. Which species is that this?

Here’s a assortment of 4 fascinating graphs. Web page 13

Grownup and first-year survival of a chicken species plotted towards 12 months and rainfall.  I ponder whether you’ll be able to guess the species?  I’ll inform you on the backside of this put up (however you’ll be able to look it up and skim the remainder of the report by clicking on the hyperlinks).

At a look, adults appear invulnerable to summer time rainfall however first years aren’t. There additionally appears to be a steep decline in first 12 months survival over time – graph in prime left – in accordance with the fitted line and the shaded space of confidence intervals. And – graph in backside left – a robust relationship with summer time rainfall. Attention-grabbing.

However cling on!  Look once more on the graph within the prime left and edit out in your thoughts the fitted line and the shaded space. What pattern do you see? I see a really variable succession of dots however since 1990 they give the impression of being to me as if they’ve bounced up and down round a reasonably flat line, however through the interval 1975-1990 there was regular decline. You can also make your individual thoughts up as as to whether the fitted line is convincing. Do this – there are 41 factors on the graph, of the primary 20 of them 1975-1994, 16/20 are beneath the fitted line – that’s a bit odd, isn’t it? And conversely, of the final 20 factors, 1996-2015, 5/20 of them are beneath the fitted line. Can that be proper?

And when you are at it, that knowledge level to the far proper of the underside left graph (with a survival of far lower than 0.2) merely isn’t seen on the highest left graph – the place did it go? Perhaps the highest and backside graphs cowl completely different years.

Nicely, I could have gotten this all unsuitable, however you’ll be able to’t say I haven’t seemed on the graphs!

3. Shifting baselines Web page 16

It’s good to see Skylark numbers recovering up to now decade of the BBS even when they’re nonetheless beneath their 1994 ranges. The BBS began in 1994 so it is sensible to point out this graph on this means however let’s not neglect that we had various knowledge earlier than BBS, and that by way of magical statistical strategies the previous Widespread Birds Census and the BBS have been joined collectively so we glance again rather a lot additional, like this: Be aware that these knowledge are for England solely not the entire UK and the final 12 months on this graph is 2021 (not, as above 2022)

The cheers for the restoration of the Skylark could also be reasonably much less muted from these of us who have been alive and noticing birds within the Nineteen Seventies (throughout which interval I first participated within the CBC as an undergraduate).

My grandson could have lived by way of a interval of Skylark improve – however he has solely seen two dots on the graph thus far – however his mum and pop have lived by way of over three a long time of Skylark decline and his grandparents have seen, and observed, over 5 a long time of decline. If we didn’t have the information, collected by volunteers, you younger individuals on the market would in all probability not imagine how widespread Skylarks have been within the olden days – however we do have the information for birds like nearly nothing else.  I rejoice the work of the BTO and others to give you the option us to look again with knowledge reasonably than with unreliable recollections.



Guess the speciesSwift.


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