Where is this all leading? Well, a couple of weeks ago now, Chris Hajduk walked into the Northwood Center with five dead Red Crossbills, all found together and probably all killed by striking the same window (untimely ends through window and car strikes account for almost all of the birds that we get brought to us). Having got over the sadness of such an event, I immediately saw this as an opportunity to add to our knowledge of the Red Crossbills that are still passing through our area in large numbers. Here was an opportunity to learn things that cannot be learned in the field. So here's some thought-provoking pictures for you (if you are squeamish, imagine the birds are just sleeping...or skip on to the next post).
Five Red Crossbills from the Cape May Coastguard Unit. Males are red, females green, juveniles streaked. So clearly here we have four males and one female [photo by Mike Crewe].
The famous crossed bill of a Red Crossbill is an amazing tool, evolved specially to deal with the seed-bearing cones of specific trees. What is intriguing is that crossbills can be left- or right-handed. Notice that the upper mandible on the male curves to the left of the lower mandible, while the female's goes to the right. In the first picture, we have three left- and two right-handed birds. Since cones tend to be symmetrical, it is unclear why there should be this difference in the birds, but perhaps it's just a random gene like our own left/right preferences [photo by Mike Crewe].
Trying to get to grips with crossbill molt strategies in five minutes proved pretty tricky for me! The main problem is that crossbills breed very early (often as early as January) and have just one molt a year, which throws all that I currently understand about songbird molt timings right out of the window! Most birds have two molts a year, usually one complete and one partial, roughly in late summer and late winter respectively; crossbills single molt is protracted and can take place progressively from April to November. However, if we look at the wing of this male, we see a set of feathers that all appear to be the same general color and with the same amount of wear. We could presume this to indicate it is an adult in at least its third year if we compare it with the next picture [photo by Mike Crewe].
A look at the wing feathers of this male reveals a set of six inner secondaries that are clearly paler gray in color than the other feathers. These represent feathers that are older and are showing more fading and wear from environmental conditions. This retention of inner secondaries fits nicely the partial molt that crossbills tend to show in their second calendar year and this bird also showed one or two greenish feathers on the body (see the right hand two birds in the first picture) [photo by Mike Crewe].
Compare the following two sonograms - sent to me by Sam Galick and made from recordings of Cape May birds - with those shown on the excellent article on crossbill types on eBird and see what you think.
Prepared sonograms from Red Crossbill type 3 recordings made at Cape May Point, November 2012 [images by Sam Galick]
Look (and listen!) for Red Crossbills passing in busy, tight flocks overhead. In flight they show well-forked tail tips and have a rather heavy-headed, full chested shape [photo by Sam Galick].
Red Crossbills lined up on the tree tops at Cape May Point [photo by Sam Galick].
As a latest update to crossbill movements at Cape May, listening for these birds is becoming more interesting this week as the last few days has seen the appearance of type 2 and type 10 birds among the type 3s. Many thanks to Michael O'Brien for sharing recordings made of these birds - and for a crazy recording that included all three types calling at once!!!