Unusual influxes of a particular bird species are known as irruptions, an interesting word that sounds like a cross between an irregular eruption and a disruption of normal experience. They’re certainly a sign that all is not normal, but it’s difficult to say whether that’s always in a negative way. It might be that a bird’s regular food source has failed, driving flocks to seek their fortunes elsewhere. More positively, that food shortage might be the result of a successful breeding season having generated unusually large numbers of hungry overwintering birds

I have a poor track record when it comes to catching up with irruption events. Indeed, I am sure that some are merely cruel conspiracies designed to sink the spirits of unwatchful or merely unlucky birders.  In waxwing winters I spend plenty of time chasing after flocks found by other people but rarely find my ‘own’ birds.  My failures are intercontinental – we happened to be over for Christmas when snowy owls started turning up all over the eastern United States in December 2013. I didn’t see one, of course, despite much craning of necks as our car crossed the Chesapeake Bay Bridge ,where a lone owl had been seen hanging out on the girders.

This year it is the turn of hawfinches, moving through the British Isles in numbers not seen for many years. Hawfinches are usually elusive, partly because they tend to be quietly unobtrusive as they feed in the treetops but also because they are genuinely scarce. Quite why this should be is not entirely known, but ongoing research by the RSPB science department is helping to unlock their secrets. It seems that as a breeding bird they favour expansive, well-wooded landscapes with a good variety of tree species and therefore a diversity of nut crops. That may explain why two places I’ve seen hawfinches in the breeding season – the only two, I should say – are the New Forest and another large expanse of woodland straddling the Hampshire–Wiltshire border.

In the winter hawfinches tend to be a little easier to find, turning up at a few ‘traditional’ sites each year. Those remain among the best places to see hawfinches during the current invasion, but the closest is at least an hour’s drive away, so I was going to need to get lucky closer to home. Through October and early November it seemed my bad luck was holding. Despite genning up on their flight call and lodging a search image in my mind – a large finch flying over with white wing-bar and noticeably chunky bill – I didn’t chance on any and a first local attempt to twitch them (on a golf course in Newbury) was unsuccessful.

My luck turned when on MSc field trip duty at Basildon Park, a National Trust house and estate near Reading. In the afternoon I managed to squeeze in a hawfinch expedition as a semi-official part of the programme, tearing eight or nine of our MSc students away from more important matters for a spot of twitching. I should have thought of borrowing students before – beginner’s luck always works and several extra pairs of eyes and ears often pay dividends too, provided everybody is sufficiently quiet. We found a small flock, four or five strong, perched in just the part of the park where recent sightings had suggested. A few students managed to fight against the dim November light to capture suitably grainy record shots to prove our success*. At the time we suspected some of the other distant flocks of birds bouncing around were also hawfinches and Basildon Park certainly continues to appeal to them this winter, with possibly around 100 birds now present.

I don’t really advocate twitching as hobby, certainly not the big-listing long-distance version, but I am reminded by events like this year’s hawfinch influx of the delicious power of rare or otherwise unusual birds to draw us outside and help us see with fresh eyes. Ordinary skies and everyday places are once more sites where anything might happen: surely the faith that lies at the heart of birding’s appeal.

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Hawfinch at Basildon Park. Photo by Kojo Acquaah-Harrison.

Here’s a short snippet of video in which I *think* hawfinches are briefly visible and audible. The small park at the end of Mercer Way in Romsey, Hampshire is an improbably good winter birding destination.

Mercer Way from Chris Foster on Vimeo.

*Sharp, full-frame true colour images absolutely do not count as record shots. They’re too good!



In retrospect, the sunlit photographs I posted of a previous visit to Leith Hill were cruelly misleading. This week we found the hilltop shrouded in cloud, though as consolation the small refreshment hatch in the tower was open for business (I reckon they should rename it ‘The Cakehole’). Nothing could be seen of the usually far-reaching views north to London and south over the Weald and Downs towards the distant English Channel. If any stray birds from a recent influx of hawfinches were crossing overhead we wouldn’t have seen them, but their call would have penetrated the murk, as did the sharp tseeps of a flock of dimly visible redwings moving through trees on either side of the summit.


Our happy field trip group in 2015, see tweet below for 2017 comparison.

Clouds or fog change the property of sound. Distances are harder to judge, the crack of a stick or call of a bird sounds closer. The world is limited, enclosed in a way that is at once disorienting and intimate. Robbed of the ability to see very far, you pay more attention to the things close at hand, observing each moss-covered stone or mushroom carefully, much as a fine coating of water droplets covers everything. I wonder how wildlife is affected; I can’t honestly say I know for sure. I can imagine ground-based predators with a keen sense of smell and excellent hearing—like foxes—using fog for cover, whilst a falcon, relying on vision, may struggle. Insects will be grounded by the dense, damp air.

While I enjoy the otherworldly effects, too many foggy days can be wearisome. We noticed many last winter, our first in the Kennet valley just west of Newbury. Perhaps it was a particularly misty season, though the relatively low-lying river valley will also be more prone to fog formation than other places we’ve lived.  Other local fog hotspots include the gravel pits at Theale. When cool air blows across the artificial lakes dense fog patches can form and drift across the nearby M4, an ironic source of danger considering that some of the pits probably contributed material to the motorway’s construction.

What’s the difference between mist and fog? Or fog and a cloud at ground level? Lots of fascinating fog facts and other weather lore on the Met Office website.


The Leith Hill views, unfogged

Last Week

This time last week (ed. Monday) I was on my way home from speaking to the Hampshire Organic Gardening Group. My subject was insects in gardens; of those two sides of the equation I’m certainly more knowledgeable about insects, but now that we’ve actually got a garden to manage I’m slowly working on my so far not very green fingers. I enjoyed the opportunity to speak at length, although I pity my audience for having to suffer the sound of my voice for 70 minutes. I don’t usually enjoy being the centre of attention (or indeed hearing the sound of my own voice) but longer talks allow you to relax into your stride: all you experience in a 15-minute slot is the initial nerves. My next public speaking engagement will be at the Berkshire Ornithological Club on March 21st next year when my subject will be ‘A birder’s guide to insects’. With insect declines making newspaper headlines in the past week, this is as good a time as any to start paying more attention to ‘the little things that run the world’.

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Speaking of the BOC, attendees at last Wednesday’s indoor meeting were treated to a masterclass in science communication from Tim Birkhead. His topic was an overview of 45 years of research on the guillemots of Skomer Island in Wales, but such is his enthusiasm for science that he couldn’t resist straying into his other (but not unrelated) work on bird promiscuity and sperm selection. Did you know that bullfinches have perhaps the smallest testes of any passerine and unique sperm morphology? I didn’t! Birkhead also featured in last week’s edition of The Life Scientific on Radio 4, from which the whistling bullfinch section seems to have been quite a hit.

Perhaps the most important finding he presented from guillemot research was the convincing hypothesis – backed up by decades of breeding data and old photographic records – that oil spilled from sinking ships during WWII caused a crash in guillemot numbers on Skomer, and they are still a long way from recovery. Despite high annual adult survival of 95% and breeding success of 80%, each female lays only a single egg* each year, so a population that slow-breeding is always going to take a long time to bounce back. Without long-term monitoring data we wouldn’t have any idea of how sea birds like guillemots are responding to environmental change, making it all the more shocking that the modest funding for Birkhead’s guillemot programme was cut by Natural Resources Wales in 2013. A successful crowdfunding campaign managed to keep it going, but the future is by no means secure. Donations towards next year’s efforts can be made here.

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Finally, on Friday I attended a performance by folk/blues guitarist and songwriter Martin Simpson. He’s an absolute megastar of the folk world, though it’s quite likely you’ve never heard of him. That’s how it often seems to go in the folk world; the bonus is that it hasn’t therefore been infected by the cult of celebrity – like most folk musicians I’ve seen, Simpson came across as very down to earth and came out to chat to audience members and ‘scribble on things’ during the interval. It was a fantastic evening: two hours of peerless acoustic guitar and banjo music, including every song from his brilliant new album, Trails and Tribulations. To tie everything from the week together nicely, a central theme of the album is our relationship to nature, with one of the original songs inspired by watching red kites soar over the Ridgeway and another by the relationship between poets Edward Thomas and Ivor Gurney, as told in Robert Macfarlane’s The Wild Places.

Somehow I squeezed all those evening events around three full days of teaching: freshwater invertebrate sampling on Monday, a field ornithology trip on Tuesday (aka going birding) and fly identification on Friday. It’s going to be hard to top that as a week of busy inspiration.