A very popular and well known term in the arena of bird identification is GISS or General Impression of Size and Shape. As you may no doubt be aware, this refers to the overall build, behavior, flying style, bill shape and a range of other factors in creating the overall feel of a bird.

In the same manner, a bird call can have an overall feel. This we refer to also as GISS or General Impression of Sound and Structure.
For the most part, like easy to identify birds, many bird calls are fairly easy to identify by call, for example the Red-chested Cuckoo Cuculus solitarius which is a very well know and easy to recognize call.


Sonogram of a Red-chested Cuckoo (Play the Red-chested Cuckoo Call).

Sometimes it may get a little more difficult when you have one species copying another and then a finely tuned ear will help identify an imposter from the real item.

As one progresses, you may feel you are ready to tackle the challenge of identifying Warblers on call alone. This is where call GISS comes into its own. Here I have highlighted a comparison of Marsh Warbler Acrocephalus palustris and Icterine Warbler Hippolais icterina. Below are the sonograms of the two species with example calls.


Sonogram of an Icterine Warbler (Play the Icterine Warbler Call).


Sonogram of a Marsh Warbler (Play the Marsh Warbler Call).

What you will notice from the sonograms before you listen to the calls is that the lines on the sonogram of the Marsh Warbler are not as sharp and steep and defined as they are for Icterine Warbler. As you will notice when you hear the calls the overall impression between the two is that the notes of Marsh Warbler are not as defined and full of bubblier, almost watery notes whereas the overall feel of the Icterine Warbler call is of a more defined clearer call but with notes not as fast as in the Marsh Warbler call. If you download the two sample calls and start to get a feel for the overall GISS of the call you will soon be able to spot the difference.

The best way to start applying this technique in the field is to be more aware of the calls around you. When you think you hear a Dark-Capped Bulbul and it turns out to be a White-throated Robin-chat copying a Bulbul, listen closely. Firstly there will be some uncharacteristic notes that do not belong in a Bulbul's call. Also when you start to get a knowledge for how a Bulbul structures its call, you will soon pickup that it is not structured like a Bulbul would put the call together. The reason for this is that although some species have an amazing ability to make very good impersonations of other species, the mere nature of bird communication will mean that the imposter will not use the same collection of phrases that the original bird would. This will result in the call being similar but structured differently. You will also notice that if you listen to a Cape Robin-Chat's call, it may have musical variations, but there is always a 4 phrases type of repetition. I have heard species do very good copies of Cape Robin-chat, but the overall 4 phrase repetition pattern is not the same and it soon becomes evident that it is not a cape Robin-chat but a good imposter.

It may all sound rather confusing if you have never attempted to tackle the fine art of getting to know your birds and their calls well, but as you start to practice you will very soon find out that it is actually not that difficult.