Definition:

(noun) A unique, distinctive field mark or other characteristic that, by itself or with very little additional information, can confirm a bird's identity. Diagnostic marks generally take range into account, since worldwide birds that share a similar marking are not likely to be present for confusing identifications. In some cases, the markings may also indicate a bird's gender or age, such as in the case of dimorphic species or subadult plumages.


Examples of diagnostic markings include:

• The long, thin, heavily forked tail of the scissor-tailed flycatcher
• The small, clearly defined black cap of the Wilson's warbler
• The sharply contrasting, well defined throat of the white-throated sparrow
• The plain white rump patch of the northern harrier

In many cases, diagnostic markings are increasingly valid when other bird traits are also considered, such as a bird's jizz or habitat. With very few of those traits noted, a diagnostic mark can confirm a bird's identification even if other field marks are hidden or the overall view is obscured. Many field guides make special notes of diagnostic characteristics, either with pointers on photos or illustrations or with notations in the accompanying text.

Birders should take great care to learn diagnostic marks, because recognizing those few, distinct markings can lead to faster, easier identification in a variety of field conditions.

Pronunciation:

DEYE-agg-noss-tik MARRK-eeeng

Also Known As:

Diagnostic Characteristic, Diagnostic Mark

Photo – Wilson's Warbler © Andy Reago & Chrissy McClarren