This morning, for the second time this week, I was standing on a well-trodden track on the Surrey-Berkshire border looking up at a couple of pine trees. This track crossed a plain of moor-grass and heather interspersed with small clumps of pines, known as Wishmoor Bottom. Since late November a flock of Parrot Crossbills has resided here, part of a national influx of this rare species.
The influx started with a large flock found on the Norfolk-Suffolk border, at Santon Downham. The numbers there peaked at an incredible 42 on one day, which is possibly the highest number ever recorded in the UK. Wishmoor Bottom was then the second site to host the Parrots, with slightly lower numbers remaining around a constant maximum of 16. The Derbyshire-South Yorkshire border was the next county boundary to be treated to Parrot Crossbills, with the forest around Howden Reservoir holding about a dozen. Most recently, 3 turned up at Broxbourne Woods in Hertfordshire (just inside the London boundary!) a few days ago.
Influxes such as this one we are currently experiencing – I wouldn’t be surprised if further flocks are found – are mainly caused by a dearth of food in the species’ usual ranges. The Hawfinch invasion that’s in the news at the moment is most likely caused by a lack of beechmast and other tree nuts in continental Europe, with the crossbill invasion probably due to a poor crop of pine cones in Scandinavia.
After a long drizzly walk from the car park to what appear to be the crossbills’ favoured trees, we waited patiently for about an hour to see if the crossbills would show up. In that time a few other birders joined us; then we received a message through Rare Bird Alert that there were 16 Parrot Crossbills present on-site, right where we were standing. There were no other birders in sight!
“Someone must be having a laugh,” one birder said; we probably would have found it more humorous if we had by then actually seen the birds.
We were just about to split up to search the other clumps of trees spread out across the Bottom when my mum and I spotted a small group of birds fly towards us and alight in the tree directly in front of us. Most dived right into the needles of the pine, although one remained perched in clear view for a few seconds, enough for us to identify it as a Common Crossbill. That was good news, at the other sites where Parrot Crossbills have been present, they sometimes form mixed flocks with Commons.
Once the crossbills within the tree had surveyed their surroundings to make sure there was no danger, they set to work extracting the seeds from inside the pine cones. This made them more visible, and we were able to see that there were indeed Parrot Crossbills within the flock! Over the next hour I was able to watch them incredibly well. Although crossbills have a habit of staying firmly out of site within the dense branches, during the time we watched them there was always at least one on show.
The above photos show the red-colouration of male crossbills, the females being a paler green colour. They also show the fascinating bill, with the lower mandible curving upwards on one side of the bill and the upper mandible curving downwards on the other side. It is unclear what determines the side on which each mandible curves, although the numbers of birds with mandibles curving each way seems to be equal. A crossbill feeds on the seeds within the cones by inserting its crossed bill between the scales and opening them and extracting the seed inside with its tongue.
Crossbills are by no means showy birds, so it was a real Christmas treat to be able to see this flock so well. Fingers crossed the influx continues and more flocks are found, possibly even closer to home!