Tuesday, 29 October 2019

Mind the gap

To the west of Box Hill you will find a narrow river valley, formed tens of thousands of years ago by the River Mole. It must have once been a mighty river, not the shallow, sluggish water course that it is today. In recent posts you will find maps of the Box Hill area with identified flight lines of migrating birds. I have marked such flight lines along the Mole Gap, but in recent weeks the birds had not been using them - until today.

I arrived at my favoured Box Hill vantage point at 06.30 hrs. It is a small area of flat ground on the scarp slope with views eastwards and, most crucially today, westwards, across the Mole Gap and on towards Ranmore. Thrushes were on the move quickly afterwards, a mixture of Redwings and Fieldfares. After approximately 75 minutes I had recorded at least a thousand of both species. By 09.00hrs the Fieldfares had tailed off, with the stream of Redwings more or less coming to a halt by 10.30hrs. An hour later I called it a day. The final totals were: 4068 Redwing and 1658 Fieldfare.

Almost all of these thrushes arrived from the east, seemingly following the line of the river. About half of them cut across the summit of Box Hill behind me and over into the gap where they headed northwards, continuing to follow the river that changes course just west of Box Hill. The other half continued parallel with the scarp before turning right (and north) up the gap, joining those birds that had taken a short-cut. Had I been sitting west of the gap at Denbigh’s or Ranmore I would have seen none of them. No thrushes appeared to enter the gap from the west. I missed a lot of birds. I was aware of high flocks and distant flocks as I was counting others. Another observer would have been helpful. I would love to have known how much of this would have been seen four miles to the east at Colley Hill. We need an army of sentinel birders placed along the counties high ground...

Today's flight lines

3 comments:

Ric said...

Steve, my own favoured (mentioned before no doubt) flight line is that of the Cook's Petrel as they take a short cut across the North Island of New Zealand from their feeding grounds in the Tasman Sea to their breeding site on the Great Barrier Island.

The flight line is really narrow. They do it at night, over as little land as possible and also along a valley flanked by high hills.

By chance the flight line takes them right over Warkworth town centre where in the right spot they can be seen passing overhead, lit up by the lights below.

I'll be there again in a few weeks. This time with the night vision optic, hoping to view them from my mother in laws house a mile out of town.

Gordon Hay said...

Steve, In a 30 minute dog walk across Redhill Common, I had 160 Redwings moving West in small flocks between 06.40 & 07.10hrs, on the same day.

Steve Gale said...

Ric - enjoy your trip and my envy of your upcoming nocturnal observations are high

Gordon - likewise, have a great time in Japan