Bobcats: How we learn what they eat.

 

As a Wildlife Biologist in the Everglades I inherited/completed a bobcat food habits study for the Florida Fish and Wildlife Conservation Commission. Prior to my Everglades arrival, from Maine, a previous Wildlife Biologist here, Mr. Bob Progulske, started a study to learn the food habits of the bobcat. Subsequently, he was promoted to another region and the study was left unfinished. But it was not abandoned. Many bobcat scats had already been collected on Everglades levees. When I arrived, I was assigned the task of completing the study, and so I started to pick up more bobcat scats.

Picking up a bobcat scat is probably much like what other people do when they pick up after their dog in the city: But they use a plastic bag while we used a soil bag. These bags are perfect for the job because they have built-in ties, are made of heavy, pervious cotton fabric and they have attached to them a very rugged, water-proof tag. Bobcats often defecate on the center of the primitive roads that exist within their home range. So, when I drove my truck on these Everglades levees, I commonly saw bobcat scats. Most of them had become desiccated in the Florida sun. But even when fresh, bobcat scat is very solid. I collected every one I found. I would place my hand inside the inverted bag and pick up the scat, re-invert the bag, over the scat, tie it off and mark the tag with an indelible marker (date and location). When I returned to the office the scats were placed in a larger marked bag inside our freezer. With this process over several years, our combined efforts collected over 650 bobcat scats!

The entire study hinged on one fact: Mammal gastric juices are not powerful enough to digest bones, feathers or hair. Alligator juices are, mammal juices are not. So, after the bobcat masticated the prey and it passed through the feline’s GI tract, the bone, hair and feathers remained undigested and remained in the defecated scat.

So if I found a way to remove all the digested waste that remained in the scat……”after digestion”, I would be left with hair (predominantly), feathers, and rarely, tiny bone fragments. After much discussion, I chose the simplest way that was available. I thawed a group of bags of scat. Then, I simply placed a few bags of scat into a janitorial bucket (the one with the rollers!) of soap detergent solution and aggressively “hand-agitated” them with one of those old-fashion mops, hoping that this would suspend the digested organics into solution and that they would simply pass through the bag’s pervious fabric. There was no way the hair, feathers and bone fragments could escape.

Then, each soil bag (still with an indelible individual number on the bag’s tag) was thoroughly dried. This required days, even in the Florida sun. Then, to my elation, when I opened the bags and began inspecting the contents for the first time……with my fingers, I discovered a wealth of hairs, some feathers and a very few bone (all of these were unidentifiable) of the prey species. The process proved to be much simpler than all of us thought it would be.

Now, when these hairs were placed under a low power microscope (let’s say 60 power?) I could see unique differences between species (or at least to genera). That is where a hair key came into play.

Credit is given to Laurie Wilkins of the Florida State Museum. It was her “hair key” to Florida mammals that was used to identify the mammals. I did pick up (tag and file) hairs from a few road-killed mammals, but overwhelmingly, it was the Wilkins hair key that made the difference.

I simply visually compared the hairs I was looking at from a particular scat (And remember, each was assigned a unique number.) to the pictures of the hairs in the Laurie Wilkins’ hair key. It was that simple. And as I looked at more of them, I rather quickly became quite skilled at identifying species with the naked eye. I analyzed 650 Everglades bobcat scats that had been previously picked up on Everglades levees, individually in soil bags and freezer-stored. That is a large sample size and so the confidence level of the results was very high.

THE RESULTS? :
Overwhelmingly in the Everglades, there are two species that are found in bobcat scats: the hispid cotton rat (Sigmodon hispidus) and the Florida cottontail (Sylvilagus floridanus).

DO EVERGLADES BOBCAT EAT DEER? Yes!
The other fascinating things that I discovered is the occasional clump of deer hair and how that deer hair behaved physically. You may already know that deer hair is hollow. Well, I occasionally found a clump of fine material that was unlike any other mammalian hair I became familiar with and was not illustrated in Wilkins’ hair key. Further, under the scope I could see that each strand of this material was HOLLOW. When “rolled” between my fingers, the material was reduced to powder. Without the use of DNA to prove my theory, I became certain that this material was deer hair and that after passing through a mammalian digestive system DID break down to a certain, limited extent. What else could the material have been? I remain convinced that it was deer hair.

WHAT ABOUT FEATHERS?
The Commission allowed me to spend several days at the University of Miami’s natural history museum to study bird skins. A bird skin is simply the feathered outer covering of a natural (formerly living) bird, stuffed with cotton (as I recall). I was able to identify just a few bird species in the scats.

Now, let’s get back to the scat that you see in this image. I can tell the hairs are from the cottontail because, although both the cottontail and hispid cotton rat hair are striated, the cottontail has a light beige or yellowish banding while the rat is simply “salt and pepper” banding. The other quality is that the rabbit hair is very fine, when compared to the coarser hispid cotton rat’s. See the two short , coarse hairs in the lower right corner? They might be hispid cotton rat hairs. You could be certain if you had a scope to pop them under. When you look at that many piles of crap you get to know. So, the hair in the scat you see here…..is at least predominantly rabbit hair.

All these scats were frozen and I did not even touch the contents of them until they had each been fully agitated in detergent solution so all the “goop” :) went into solution and passed through the bag’s fabric. Then, still in the bag, the hairs were completely dried. Then, and only then did I handle the material that had been through the cat’s GI tract. And that material was 100% benign.

I have to admit that I did not finish completing all the monotonous manuscript revisions. That was my fault. But with the help of many others, I did complete the physical study. And we did learn a lot. But it should be mentioned that it was quite common knowledge then that the hispid cotton rat and cottontail were mainstays for the bobcat. The big discovery I think was that the hollow deer hairs were there too (at a much lower frequency than the rat or rabbit) and turned to powder when pulverized between the fingers. The Commission held the results and the manuscript and I am certain that it was published.

All of these results occurred years before the release of the deadly Burmese Pythons into the Glades. And that was a tragedy. This snake has wiped out upwards of 90% of native mammalian species.

Robert King
Dec 26, 2013, revised Jan 4, 2014

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