Visible migration; Horrid results for the thrushes

Fot this blogpost, we can get the old Medway texts out of the way right at the start:

Holloway (1985): (migration not mentioned!)
Davenport (in Oliver, 1991): "..at the same time (last three weeks October/first two weeks November) calm, misty days might produce overnight falls of Blackbirds, Song Thrushes and Redwings.. while the continuous calls of these three species migrating overhead typify many autumn nights.."


Blackbird

This typifies the problems here. We know the numbers come in from the continent, but as a mainly nocturnal migrant it is hard to pick out the arrivals. There were few peaks out on the Point of Horrid Hill, but prior to that the small build in numbers through the season more likely reflect local dispersal and a breakdown in size of defended territories.

The one thing I'll also mention is our subconscious desire for birds to be migrants. 'Scaly' plumaged Blackbirds must be continentals. Dark billed birds must be continentals. Nope.

Since I moved back, local orchard ringing of a very late brood of Blackbirds saw a nice retrap of a scaly youngster late in the autumn. Several years ago another ringer had a breeding Scaly bird on the Hoo peninsula. As for bills, birds from late broods keep them much later than early brood birds. We cannot assume such birds are 'contis', we just wish they are. They might well be, but we can't presume.


Fieldfare

Well I wouldn't have forecast this graph a few years back, bearing in mind the good ol' days at Grain when flights over the Thames often appeared; here, none crossed the Medway estuary waters this year. The only movements recorded were from the mound on the southern shore itself.

I have a theory (when you have so much thinking time on a viz mig watch, such things happen).

For the past five autumns, my first Fieldfares along the southern Medway have been birds in, or over, orchards. Why that would be, when they don't start on the windfall until later, is hard to suss; perhaps it mimics a favoured habitat? Who knows? The white circles note my sightings for first three dates each autumn, all in orchards. (The northern half of the Ham Green peninsula is a main attraction.)

So, birds at the end of their migratory flights might head for this habitat (certainly in spring I've had flocks cross north from Ham). Flighting autumn birds often move from this area to just inland out of sight of my two Horrid watchpoints; they do cross from Ham to Motney and sometimes to Bloors, but look to the orchards just south of the estuary wall for their flightlines. The few days I have a major pump, I wonder what it would be like if I were watching just south of the railway line around Pump Lane..

A reminder that one small observation point can show viz mig, but may well not tell the full story of the viz mig in progress.


Song Thrush

I blame my years living among flood plain fields in East Sussex for Song Thrush being my favourite migrant thrush. From Horrid hard to spot the movement unless you look daily, but it appears to be discernible here (just).

In general, Song Thrush have a steady (broad) route along the shore, or just inland. Back in 2013, mapped the route south-west of the Medway Towns, as if some really didn't like the concept of overflying urban sites unless they had to. If still truly 'migrating', overflying the Towns during the first few hours of daylight would surely not be as great a deterrent?

Redwing

Only picking up one big arrival was a pain, but it went the way things do; a big south- southwesterly element to the flight, high in over the water at first light. Otherwise, the (mainly) westerly tracking evident in all of the smaller daily movements.

As with Fieldfare, autumn movements more easily noticed over better habitat inland of the estuary.

Of course, both Redwing and Fieldfare are great cold weather movers in this part of the world. Arrivals can be late, returns can be immediate; Lack's radar studies in the sixties showed flocks of these (and Starlings) crossing from the continent one night, flocks moving back as soon as the thaw set in. Why roosts for all three can be temporary and fickle around here.

(Now do I make that my excuse to make 2018's viz mig season last from mid-June to December 31st?)