Wednesday, 9 March 2016

Say hello, wave goodbye



Spring fever is upon us. Anticipation among birders for their 'firsts' of the year is now building, thanks to the odd Little Ringed Plover and Wheatear appearing in the UK. Searching for 'firsts' has always been easy. Searching for 'lasts'? Never seems to appeal as much to birders. Often you don't realise for a few days that 'x' hasn't been seen for a while. Makes getting a feel for departing common species all the harder.

Take Dunlin.

On my 'register' for waving off during March, and in line to be my 'blog bird of the month' over several coming posts.

There are three races that use the UK.The breeding population is Calidris alpina schinzii. The evidence points to them spending the winter in south-west Europe and north-west Africa and, like many British returnees, they favour a western route home to breed. Not much need to touch Kent.

C.a.arctica, from Greenland are transients, again mainly by-passing the south-east en route to and from west Africa.

Which leaves C.a.alpina. The vast majority of Dunlin in the UK for the winter are this race.

At this point I'll remind you the Medway estuary is 'inland'. C.a.alpina that have wintered at other sites around southern England and down through France will stick to the Channel in transit; why coastal sites pick up on many more spring/autumn movements than seen within the 'inland' estuary here. When I worked near Rye in East Sussex, tripped over them in September, here the Medway's first real numbers aren't until October, and spring effectively finishes in March- not many drop in.

But most breeders aren't back on territory until late April at earliest. Where do the Medway birds go in the interim?

The Waddenzee. Just as in the autumn, over on the Dutch/German border the Waddenzee is the transit hub. Leave the wintering grounds, go part-way to feed up there and await conditions for making the return at just the right time. Ringing has shown that waders in the south-east depart without putting on fat reserves. Ringing has also shown that on arrival on their breeding grounds they will be carrying additional fat, in case the weather turns nasty. Dunlin are heavier in spring than autumn. Dining out closer to the breeding grounds means they can pile it on and not waste it all on the journey. Saving nearly 600 kms off of a 4,200 km urgent flight must help.

Now here's a question I've had since I got back to the Medway three years ago. How representative are published figures to date for March Dunlin on the Medway? Taking a mix of WeBS and individual counts from the county bird reports it was clear that there perhaps wasn't as much known as we might think:


Having served a short period as North Kent recorder, I found myself reading several things into the pattern based on my own biases.

First, the large drop in numbers in recent years could well be down to incomplete WeBS coverage. Then for pre-millennium, the variance in high/low figures could be weather related- departure delays/advances are a possibility. Of course, it could still be other factors. If count dates move, then this could have a knock-on; the 10th might be a lot different to teh 20th. Individual counters covering important sectors out of synch, perhaps at later dates than a WeBS core date, might mean birds have exited in-between.

My niggle. Many 'general' birders are unaware of the importance of boundaries. Already their counts might just be noted as 'Riverside Country Park', while in reality they had only visited one part of the park. And their submissions wouldn't note time or tidal state. Really tough for any Report compiler to make use of what had been received when trying to write any meaningful account. If the boundaries aren't publicised widely, how can birders appreciate them?

At some point in March, we can reckon on numbers dropping away here. Part of why I set myself a target of getting counts for all areas on the south shore during each ten day period. First year back, 2013, I coloured me red throughout the whole of March, and April was pretty darn orange, thanks to a prolonged cold snap. In the mild March of 2015, the exodus happened right at the start of the second ten-day period. And of course, I don't count the northern shore. It seems likely the whole estuary is being under-represented. The County Society acknowledged this a few years back- "it is likely that some counts presented in the tables under-estimate the true totals" even after including all received "higher non-WeBS counts in the tables".

So, any count, any time, is of value. If you are an estuary birder reading this (any estuary), I'm sure your county Society would love you to pieces if you provided them with this sort of additional information. For the Medway I intend to complete my 'where to watch guide' on this blog by this coming autumn, including referencing all BTO WeBS/ Low Tide Count core areas.

Although I record my inter-tidal counts to a much smaller scale (I have too much time on my hands, clearly), each count is cross referenced to the relevant BTO Low Tide Count area, so I can produce comparative charts for all the more common species. The BTO map (with a north south divide in red for my purposes) of the Medway appears below:


which for my purposes becomes


so that all my counts of Dunlin during these first ten days of March this year end up looking like


And not a number in sight. Of course, my mantra is not to count for a number, but to count to understand. Besides, I've had to spread all these counts over a nine day period (I've got tomorrow off, I think I'll go birding) so there really ought to be some Dunlin duplication in there. But this of course mimics Low Tide Count methodology, setting out to show the importance of various areas during a period of the tidal cycle. Now of course I wouldn't be normal if I didn't think I have a reasonable idea of just how many are along the southern shore (it's around about orangey-red, give or take some light blue). Joking aside, my fun this month will come from comparing this map to the counts I'll be mapping out between the 11th-20th and 21st-31st. Watch this blog.

I hope that's nudging a few readers to think about ways to spice up their own 'last sightings'. All those 'first dates' can wait a bit longer(!)

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