Naturespeak A naturalist's view of the world

June 9, 2008

Beak Business

Filed under: Uncategorized — wykes @ 8:32 pm

 

  You know about the “bird in hand” thing already, so you shouldn’t be surprised that I am here holding yet another dead one up to your face.  This window killed Great Crested Flycatcher will give us a chance to appreciate a feature that is hard to see on one – or even two – in the bush. The business end of this species, the wide powerful beak, is lined with whiskers. Since birds can’t have real whiskers, the question comes up as to what these things really are. While we’re at it, let’s discuss why they have them as well.

  First, let’s look at the general features of this large flycatcher. True to their name, their grey head is topped with a low crest – more of a cone-head actually. The belly is a nice light yellow (see here) and the back is greenish gray with touches of cinnamon on the wing and tail feathers (see here).  The Great-Crested is a woodland bird that prefers the rarified air of the high tree tops. It is heard more often than seen – issuing explosive “wheep-wheep-we-ep” calls at arbitrary times from above the leaf cover.

  As a member of a group of birds called the Tyrant flycatchers, or kingly flycatchers, these birds are primarily insect eaters.  They feed by flying out from a lofty perch in a series of short sorties much like a fighter jet on a mission. Their on-board weapon is a wide triangular beak that audibly snaps shut on its prey like a miniature steel trap. This gets us back to the subject of that beak and those whiskers – or what-ever they are – that line it.

  Officially, these “whisker-like” structures are called rictal bristles (not rectal – rictal). It seems un-necessary to have a special anatomical name for the corner of a bird mouth, but there is one and it is called the rictus.  The vaneless and barbless feathers that line the rictus are therefore called rictal bristles, but similar feathers elsewhere on bird bodies (such as those on owl’s foot or around the eyes) are also given the same name.

  These simplified feathers form a fringe around the mouth that has led some to conclude that they function like a basket to trap near-miss prey. They do create a loose comb around the open mouth (see here). Others have concluded that they form a screen to protect the eyes from flying bug parts.

  Experiments on a similar species have dis-proven the bug net idea. Apparently, researchers cut off the bristles on several subjects and compared their insect catching efficiency to un-shaven birds. There was no difference what-so-ever. Because shaven birds ended up with a little more dust on their eyes, the possibility of eye protection remains a viable option. Since bugs are fiercely snapped in mid air, it is probable that many are “rent asunder” by the impact. Flying heads, legs or wings could be deflected away from the vulnerable eyes. Human Motorcyclists that know what it is like to be struck by an insect at 65 mph can empathize with a flycatcher deliberately targeting the insects at 20 mph or so.

  Perhaps the most remarkable thing about these “whiskers” is that they may indeed function something like real whiskers. There are sensory corpuscles at the base of each bristle that transfer touch information. Whether these creatures can use this information like a mammal uses whiskers has yet to be determined.

  There is one other unanswered question that surrounds the Great-Crested Flycatcher. They are cavity nesting birds that habitually line their nests with snake skins. There doesn’t appear to be any reason for doing this since it does little to deter nest robbing predators. In today’s junk littered landscape this flycatcher also makes use of wax paper and plastic wrappers, so it is likely that they just have a textural decorating thing going.

  

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