Thursday, October 14, 2010

It ain't like the picture in the book...

I know the photos are broken. I'm working on it.

Most people who have spent much time using field guides to identify animals know that what you find in nature does not always look like the example drawings and photos displayed in the book.  It is impossible for a single picture, or several, to represent the full range of variation typically seen within a species, let alone the aberrant individuals that look nothing at all like others in the same area.  For that reason it is important to learn multiple field marks for each species and in many cases, use what is available to rule out similar species.

A recent thread on the Field Herp Forum demonstrates this quite clearly:
Variation in P. Cinereus

Red-backed Salamanders are known for being quite variable but speaking honestly, there could have been a similar thread for every species of herp on the east coast.

For example, here is a photo of a Northern Dusky Salamander, Desmognathus fuscus, that is solid orange (they are normally dark brown or solid black at this size):


One of the best field marks for identifying a Northern Two-lined Salamander, Eurycea bislineata, is the bright yellow pigmentation under the tail.  And yet here it isn't:

This past spring I encountered a Salamander that did not look like any others I had ever seen and I think it makes a great example to demonstrate my point.  Here it is:

Leucism is a form of albinism in which pigment is entirely lacking from the skin but remains in all other tissue, including the eyes.  The result is a completely white animal with no useful markings or patterns for identification.  This salamander looks pink, except on the tail, and this is because you are actually looking through the skin at capillaries.  I will use this Salamander as an example of how to successfully identify these oddball finds.

With such an animal the important thing to do is to start at the most basic level and rule out other genera and species rather than jump immediately to any conclusions.  Usually there are some species you do not need to rule out.  We know it's a salamander so we can start there.  Geographic range will immediately help.  This Salamander was found in Vermont and the only species to choose from are:

Eastern Newt
Blue-spotted Salamander
Eastern Red-backed Salamander
Four-toed Salamander
Jefferson Salamander
Spotted Salamander
Spring Salamander
Northern Dusky Salamander
Northern Two-lined Salamander
Mudpuppy

There are certain species on that list that are so different that we can rule them out without thinking twice.  The Mudpuppy, for example, always has external gills and never leaves the water.  It is also nearly a foot long, so it's off the list.  We can take the Newt off too because the specimen found did not have dry, rough, skin.  While there is no reference for scale in the above photo, this salamander was much larger than a newt.

In Vermont there are two body shape/size categories of terrestrial salamander.  The small, slender-bodied Salamanders include Eastern Red-backed, Four-toed, and Northern Two-lined Salamanders.  The larger, more stocky salamanders include the Ambystoma genus, Northern Spring Salamanders, and Dusky Salamanders.  Based on the provided photo, the size of the salamander alone should rule out the small and slender species.

For example, compare the Eastern Red-Backed Salamander, Plethodon cinereus:

to the mystery salamander which is about the diameter of my pinky:

Ruling out something like a Spring Salamander, Gyrinophilus porphyriticus, can be done using shape.  The salamander found has a somewhat short but very rounded snout:

Whereas Spring Salamanders have a more truncate/flattened snout:

While the salamander found has a slightly laterally-compressed tail it is very round in cross-section compared to a Spring.  The end of a Spring Salamander's tail is blade-like:

Usually when identifying a Dusky Salamander you look to see if there is a light line from the eye to the back of the jaw.  This field mark is completely useless when it comes to Leucism.  Shape and size can be used to rule out the Northern Dusky Salamander as well.  The salamander pictured would be EXTREMELY large for a Dusky, though not unheard of.  Dusky Salamanders also have very small front legs relative to the back as seen below.  Yes, all salamanders have larger hind legs than in the front but this difference is exaggerated in Duskies:

What is left is the Ambystoma genus.  Is it a Spotted Salamander, Ambystoma maculatum?  The important part of the body to look at will be the head.  This specimen has a fairly narrow head compared to that of a Spotted which is known for having a short, rounded, wide head:

The mystery salamander:

And a Spotted Salamander:


The only options left are Jefferson Salamanders, Ambystoma jeffersonianum, Blue-spotted Salamanders, Ambystoma laterale, and associated hybrids.  I included a photo of the vent to show you that this individual is a male.  Males have swollen cloacas during the breeding season, when this individual was found, and hybrid salamanders are effectively all female (over 99% and we've never seen a male hybrid in VT).  Because this is a male we know that it has to be either a pure Blue-spotted or pure Jefferson Salamander:

Vent:

I'm sorry that I do not have a better photo of an unswollen female vent:

Looking at the head again, remember that our salamander had a short rounded snout.  One analogy I like to use when comparing Jefferson and Blue-spotted Salamanders is that the two species have heads sort of like Volvos or VW bugs.  The Jefferson has a elongated, truncate, squared off head that reminds me a lot of an old Volvo station wagon.

Blocky Jefferson Salamander glamour shots:


and


compared to a rounded Blue-spotted snout:

For comparison, here is a Volvo (Jefferson):

and a VW Bug (Blue-spotted):

Our mystery salamander looks a lot more like a VW bug:


While the mystery salamander does have a somewhat laterally-compressed tail, its tail is rounded in cross-section relative to a Jefferson.  Take a look at it one more time.  I'll be cheap and use the vent shot again for this:

Now a Blue-spotted (in a defensive pose):

And a Volvo, I mean Jefferson

While the Jefferson Salamander does not have a tail as knife-like as a Spring, it has much more laterally-compressed one than a Blue-spotted (and our mystery salamander).

Finally, if local range data is available, you can use that.  I found this salamander in a part of Vermont where Jefferson Salamanders and associated hybrids are not known to occur and at an elevation (lake level) that is more typical of Blue-spotted Salamanders.  (If you are herping in Vermont, you should check out the herp atlas website -- it has range maps current as of 2005 with an update coming in 2011!)  The mystery salamander is a Leucistic Blue-spotted Salamander.  Here is one of his friends found on the same road just 5 minutes later:


A good field guide, while inherantly limited in the number of pictures and illustrations it can provide, should provide enough detail in its physical descriptions of each species to allow for the successful identification of even the most unusual sightings; it just requires some fine attention to detail on your part.  For folk in the eastern Great Lakes Region and New England, I like the New York guide.  It has the most detailed information available in a portable field guide and a variety of photos to compliment each species description: Amazon Link

Next week: How to differentiate larval Dusky Salamander species using smell.  I've almost got the "click to smell" system up and running but am having trouble getting it to work with PHP5.