It stands for 'visible migration' and today (from my limited experience) was pretty good!
I was out in the field this morning just after sunset. It began with a flat tire which clearly wasn't a good start especially because Vestamager is an expansive area and I wanted to get to all the good spots. That wasn't going to happen - but in the end it wasn't so bad because there were many birds.
Right from the beginning there were constant streams of flocks of small passerines passing overhead. 10 - 300 at a time.... on flock after another. They rarely stopped to let me ID them but from what I had read and heard from other birders I expected they were mostly Chaffinches, Bramblings, Tree Pipits and Meadow Pipits.
I don't think I've seen a 'vis mig' like this in North America (NA) before and I don't thing that it even occurs for most passerines. Blue Jays migrating along the north shore of Lake Ontario and Lake Erie comes to mind but even that doesn't compare. Most NA passerines migrate at night (resulting in awesome radar images) and one can often listen to the calls at night to help ID them. But nothing beats actually seeing the birds passing overhead during the day.
Eventually I did come across a few flocks of each of those species resting or feeding.
Meadow Pipit:
Note the white eye-ring and thick streaking on the sides to distinguish it from other pipits.
This Northern Wheatear landed right above my head:
Later down the trail I came across several large flocks of warblers which made me feel right at home. Except that these warblers don't let you get good looks, they're much more difficult to differentiate (they're all pretty bland) and I only know of a handful of species that I should expect to see. Nevertheless I eventually found 3 Blackcaps which was a lifer for me.
Around noon the vis mig was pretty well finished and I headed for the lookout:
From there I saw several thousand Barnacle Geese staging, along with several Greylag Geese and a family group of Greater White-fronted Geese which is pretty early for that species!
Greylags:
White-fronts (a different sub-species from the one seen in western/central North America):
And despite it being difficult to get a look at the warblers let alone take a picture I managed this one of a Chiffchaff:
It seems that there was an influx of Yellow-browed Warblers in the region today. With at least 5 individuals seen today whereas in most years there are only 1-3 seen in the autumn.
Three were seen today at the Copenhagen harbour which happens to be about a 30 minute bike ride away - so perhaps I will make my way over there tomorrow morning.