It was already very hot at eight o clock on one of those dead calm days in the sweltering last week of June. As we made our way up towards the top of Dalkey Hill we encountered two Painted Lady butterflies, summer migrants who might have begun their journey south of the Mediterranean. A few minutes later we came across some more summer migrants but these were, unusually, summer migrants that come from the north rather than the south We heard them before we saw them, that distinctive ‘chip, chip’ call they make when flying, then we saw the flock passing over with their characteristic bouncy flight. It was a flock of Crossbills and, although some crossbills breed in Ireland, the flocks that arrive in summer are nearly always what are known as ‘irruptive’ flocks who leave breeding grounds in Scandinavia when food is short and head south in groups of varying sizes. Their name, unsurprisingly, comes from their bill, whose top and bottom mandibles don’t meet but end in opposing curves which can go either to the left or right.
    Their main food is conifer seeds and the bill is used to prise open and wedge apart the scales of the cones so they can then pluck out the seed with their tongue. They are born with ordinary straight bills which gradually curve as the birds grow. Seed production on different species of conifer trees can be very variable with bumper harvest some year and very little other years and it’s in the scarce seed years in Northern Europe that numbers of these birds arrive. They are one of the earliest nesting birds, often raising young in late winter, so the juveniles will be well advanced and well able to fly when they set off for Ireland or the UK.
   Crossbills have been fairly regular summer visitors to Dalkey Hill over the years and tend to gravitate to the same groups of conifers, the Douglas Firs and Spruce between the car park and the aircraft beacon and the nearby Monterey Pines where they’re easily heard but difficult to see, almost resembling pine cones themselves especially the dull green coloured females. You might detect indistinct movement between the pine needles and then a dozen birds might fly out of the branches.

Some of the flock on a Douglas Pine.
The males are brick red and orange coloured      Photo: Michael Ryan

     As far as I know they are the only creatures that can access the seeds in Monterey Pines, the cones of which are like large wooden handgrenades (you really wouldn’t want one falling on your head!) and are even inaccessible to squirrels but no match for the crossbills powerful beak. As mentioned their call when in flight is a ‘chip chip’ sound but when they’re feeding in the trees they make a loud metallic trilling call. Three weeks later we heard a flock again, it flew over us, between thirty and forty birds and landed in the same area as before. This time we were lucky to get good views of the male birds among the flock, with lovely brick red blending into shades of orange plumage on their body and rump. The female’s plumage is green blending into yellow and unusually for a bird species individuals of both sexes can have variable colour schemes. We saw one male bird scolding away another and watched them high on the Douglas Fir branches, with one acrobatically hanging upside down to get at a fir cone.