Friday, 13 May 2016

Gestalt - Gestalt Keys (The Head)

For those new to gestalt and gestalt keys please read the introductory post (HERE) and the essential principles of gestalt keys (HERE) before proceeding.  

In the posting on Primary Projection (HERE) I described a useful method for aligning the body and wings properly in side profile.  By looking at the bird from a slight elevation the tips of various feathers of the opposing wing can act as a useful guide to line up the body parallel with the plane of the camera.  

Of course, having the body in side profile is absolutely no guarantee that the head will be aligned similarly.  The head and neck move very independently of the body.

Whereas the wings provided a handy clue to the alignment of the body relative to the camera lens, the head doesn't give up such secrets easily!  There is only one structure that we can rely on to definitively say the head is in side profile.  That is the bill.  Everything in side profile is foreshortened, with the possible exception of the length of the bill measured along the culmen.  So how do we confirm that the head and bill are in side profile?

In some species it may be possible to look straight through the nares (nostrils) when the bill is viewed in perfect side profile.  Rather like the sight in a rifle, the narrow bore of the nasal passage restricts our view to within a very narrow angle. So there is little margin for error.  This method takes care of the problem of rotation about both the X and Y axes.  This makes it one of the more effective tools for judging side profile of the head and bill.

Glaucous Gull (Larus hyperboreus) here and Iceland Gull (Larus glaucoides) are sometimes separated using complex formula involving bill and eye proportions (from New Approach To Identification, Grant and Mullarney).  It's useful to be able to confirm that the bill is in perfect side profile by being able to peer through the nares.  Note it may be convenient to photograph a bird backlit as it is here, to illuminate the nares chamber and help verify the angle of view.

Eye to Bill Ratio
In the posting reviewing the limitation of this measurement (HERE) I highlighted some of the issues with this commonly-used tool.  As with most comparative measurements in common usage the eye and bill don't actually align along the same axis.  So we cannot hope to measure an anatomically accurate eye to bill ratio from our images.  What we in fact measure is a two dimensional projection of these structures.  Rarely is an attempt made to actually define whether it is the eye or the bill that should be in profile for this test.  I think it's pretty clear that the bill should get priority as explained above.  But very often the images we see tend to show the eye more in profile, because this is more aesthetically pleasing perhaps.  Or, because birds, being curious creatures, tend to look at the camera/observer much of the time, which means the image captured is often of the eye in side profile.

For birds which possess a symmetrical bill, and provided one has a good series of shots to work with, it should be possible to establish side profile closely based upon eye to bill ratios.  Ideally the available shots should capture a bird in the process of turning it's head through the parallel axis, i.e. from looking slightly towards the camera to looking slightly away (as shown above).  Video can be useful for capturing this perfectly.  With luck, at least one of the images will show a perfect side profile view.

This method doesn't provide confirmation of a side profile view but it should certainly very closely approach it.  Another slight flaw with this method is that it doesn't deal with rotation about the X axis.  For example in the top image inset of an Eastern Olivaceous Warbler (Iduna elaeiaca), while the bill can be aligned closely to the X axis, it is clear that the angle of view is from below (we can see part of the underside of the bill for instance).  Similarly with this Ring-billed Gull (Larus delawarensis) the bill is rotated slighting towards the camera along the X axis in all images.  This is because I was elevated above the bird when I shot these images.  So, unlike the Glaucous Gull image above we can't see straight through the nares in this instance.  This viewing angle is further confirmed by the fact that we can see the base of the culmen in all images, something which wouldn't necessarily be possible if we were looking at the bird's head perfectly from the side.  This doesn't ultimately affect the eye to bill ratio but it may impact on a measurement involving the Y or Z axis (such as those used in the Glaucous V Iceland assessment tool).

Mapping of Features
These methods alone may not give us the required confidence in some cases to take reliable measurements in side profile.   Once again we turn to Gestalt Keys.  In the introductory postings I showcased a couple of prototype keys illustrating structural angles of the head.  With thanks to some valuable input from Pete Dunten I have done further work on the Dowitcher Loral Angle key to improve side profile alignment.  It is clear that in order for a feature like loral angle to succeed the head and bill must be in perfect side alignment.  The key requires a number of hard and soft loci to achieve this and that indeed may prove to be the case with most gestalt keys involving the head.

I am not quite ready to make this key widely available through the blog as I feel it needs more testing and refinement, but if anyone is keen to have a go using the current version "warts and all", drop me an email and I will send it on to you.

Tuesday, 3 May 2016

Gestalt - Ringer's/Bander's Guides

Field-based bird identification has essentially been approached from two directions.  Gestalt or 'jizz'-based identification draws on the aspects of a bird's morphology and behaviour that make it distinctive.  In the mid 20th century early bird guides described a fairly rudimentary approach to field identification.  This became increasingly revolutionised until, in the early 1990's The NEW APPROACH to Identification (Grant & Mullarney) delivered a more focused approach, based on finer details, including morphological and topographical features, fine feather detail and field marks.

Whereas the intimate study of fine feather detail was once the reserve of the ringer (bander) and those with access to skins and museum collections, the rise of much better field optics has given birders more options, allowing us to embrace 'the new approach'.  For many it has become 'the normal approach' to bird identification in the field today.  That said 'jizz-based' field guides have also continued to co-exist and many birder's favour a balance between these two approaches.  Modern field guides cram in an awful lot of detailed information, stressing a combination of a bird's morphology, field marks and vocalisations.  But it's not practical or often helpful to include every known identification criterion for every species.  For those looking for a little more detail however there are some very specialist identification guides, focusing perhaps on rarities or on particularly difficult species pairs or families.  Then there are the ringer's (bander's) guides, which are very specialist indeed, intended primarily for those who trap and ring (band) birds for long-term population or migration studies.

In 1970, more than 15 years before the late Peter J. Grant and Killian Mullarney first published The NEW APPROACH to Identification in the Journal Birding World, Lars Svensson had already published the first edition of his ringer's bible, Identification Guide to European Passerines.  Meanwhile, in North America, promoted by Svensson's work, Peter Pyle with the assistance of Steve Howell, Robert Yunick and David F. DeSante took on the same great challenge and in 1987 published their Identification Guide to North American Passerines: A Compendium of Information on Identifying, Ageing and Sexing Passerines in the Hand.  This has since been followed by Peter Pyle's Identification Guide to North American Birds Volumes I and II.

In many ways 'the new approach' significantly bridged the gap between contemporaneous field guides and a Svensson or Pyle compendium.  But even to this day few field birders would try and incorporate a ringer's guide into their birding tool bag.  For most, the level of patience and luck required to be able to observe the finer identification pointers referred to in one of these books on a bird in the field simply doesn't justify the effort required.  And yet birding has continued to evolve.  When the digital camera emerged in the late 1990's bird identification began to take another giant step forward.  Through digiscoping and the proliferation of digital SLR's birders can now capture details relatively easily which wouldn't have been considered possible in the past.  Birders can now start to consider identifying bird's based in part on manuals intended for those who identify birds more typically in the hand.

Leafing through a Svensson or Pyle one will find references to ageing, moult and detailed biometrics in addition to the more standard field marks one might expect to find in a standard field guide.

Springtime brings large numbers of Chiffchaffs and Willow Warblers from their southern wintering grounds to the shores of Northern Europe.  Adults at this time of year can be more similar than juveniles in Autumn, particularly in terms of their subtle colours.  Freshly arrived they can be a bit tamer than usual.  I was recently afforded the opportunity to obtain really close views and photographs of this newly arrived Willow Warbler.  With longer wings than Chiffchaff, Willow Warbler migrates much longer distances from Southern Africa to Europe.  Leafing through my copy of Lars Svensson's 4th edition I was guided through some of the more subtle details revealed by this bird's wing.

You may note I have chosen to caption this blog posting under the Gestalt series of postings.  I could have just as easily chosen the Field Marks series.  However it is in terms of Gestalt that I am considering aspects of morphology and it seems to me that much of the ringer's (bander's) treatment of birds in the hand is about a detailed look at morphological traits that separate similar species including, in particular biometrics and wing structure differences.  I am sure I will be writing more about this area in the future.  For now this has been a taster.