Harried by the tide

A 6.3 spring, with a 0.3 surge topping out six minutes before sunset? That'll do.

Twisted arms, got a lift out to Shoregate from a chum. Essentially looking for a negative result on the islands Marsh Harrier roost. Score. None moving over the water either, just normal numbers over Chetney, but a handful showing interest in Barksore.

The island roost is always used on neap tides, in preference to those two sites ashore, both of which are shot. But on springs, the Harriers have to stay landward. Morning flight behaviour also changes. Birds moving out over Ham Green and then north-west via Motney and Nor then tend to stick around the western basin. The small roosts in the eastern basin remain in the same small numbers. (Interestingly, these are often young birds.)

The islands at low tide

The same, spring tide

This might seem odd behaviour, when birders mainly only talk about the main roosts in permanant use on the marshes, but birds do chop and change- radio-tagging elsewhere has shown they might well use up eight different roosts in a winter.

The next thing is that these could be dismissed in the past as pre-roosts. Actual roosts are usually not entered until sunset or just after; for the main site, whilst birds will have been in that vicinity for some time, most arrive at the alloted hour, and come from borth east and west. The two minor roosts are certainly used as such, having had the experience of inadvertently stumbling upon a flattened reed platform complete with Harrier one pre-dawn morning (it was in a little-used net ride of mine).

The map shows neap roosts (yellow) and spring roosts (orange), with usual flightlines. The roosts haven't quite been positioned correctly, but the locals know where they are. The Medway might not be up to eastern Sheppey spectacle standards, but a busy evening with a couple of dozen birds up in the sky will always do. Or even one or two at a smaller roost, really not fussy.