How a deer dissolves
Freeze frames from motion-cam video are helpful in judging relative animal size. Cropped exactly the same, smaller bear is overlaid on the larger as a photoshop transparency and traced.
Steve Merli and I have slightly refocused our motion-cam deer study from behavior of live deer to behavior of dead ones. In other words; what happens after they die, and begin returning to earth. Turns out that motion cams (trail-cams, or game-cams if you prefer) are excellent tools for this study as well
The vimeo below tells most of what we’ve learned from what you might call Decomposition, phases 1 (birds) & 2 (bigger carcass-crunchers). Maybe I’ll post a sequel later for phases 3 and beyond—for at least as far out as we can find recognizable pieces of deer on our camera sites. My slideshow works as a stand-alone, but before launching, you may want to read about some stuff I noticed after posting. It might help interpret some behavior not commented on.
In the narration you’ll notice I avoided referring to the first bear as ‘he’ or ‘she,’ for lack of certainty. I’m now leaning toward female. After putting together the vimeo, embarrassed that after viewing over 100 ten-second movies I still wasn’t positive about gender, I looked closer at them. A large bear scat shows in lower left of all .avis taken after 4:02pm on May 16th. We didn’t catch the bear in the act because the camera takes 5 seconds to ‘prime’ in between movies. But just before that, we did catch a urine stream, one of the better clues to sex of a bear.
Oddly, considering how much commoner black bears are than brown, continent-wide. I see few tips online for distinguishing male from female Ursus americanus. But ADF&G has a great pdf on that subject for brown bear ID. It shows difference in urination posture for males (forward-leaning), and females (rear-leaning). Our bear leaned back and peed straight down. Presumably, most of the ID-features listed by F&G for brownies work also for blacks? If anyone has knowledge in this area, or if you notice mistakes in my interpretation, I’d love to hear from you.
The ADF&G guide also has clues to bear size. On younger brown bears, head and ear size looks proportionately larger than on mature ones. This clearly works for sizing-up black bears as well (and for that matter, many other mammals).
PS: Wyoming Fish&Game has a 6-minute youtube explaining sex differences in black bears (Hopefully you like funky country background music). Mentions many of the distinctions noted by ADFG for brown bears, including forward vs rearward urination posture, head-breadth and ear spacing. If you watch this video, disregard the info on male-female weight and track-width thresholds. Our black bears are larger. When we traveled with Wyoming naturalist Doug Chadwick on Kuiu Island (no brownies), he had trouble believing that the large scats all over the logging roads were from black bears. Kept saying: “If I saw this turd in Wyoming I’d swear it was from a grizzly.”
What made the first bear’s sex of particular interest was behavior of the second. On arrival, the small bear walked directly to the substantial bear-poo (something its maker had never done) and sniffed, showing no alarm. I later compared notes with Riley Woodford, who has experiences with motion cams on carcasses in his work for AK Dept Fish & Game. At one of his camera sets, a smaller bear visiting the cache was clearly nervous. Our small bear’s casual behavior, less than 90 minutes after the larger one left, makes me wonder if it’s a recently separated cub.
(PS: July, 2020: Steve and I kept our cameras on these deer until they were just piles of nearly odorless bones. See my update, Decomp-3&4, which contains surprise errata concerning my gender-guesses from this first entry.)
As for size-difference, it can be surprisingly hard, watching these videos, to judge relative mass. Shape-shifting bears can look slinky one second and bloated the next. Jet-black coloration makes it hard to make out contours, especially in videos with contrasty light. Trying to convince myself the second bear was indeed smaller, I finally took screenshots of both of em, facing right, standing in the same location. Overlaying these pics in photoshop and toggling suggests the little bear may be less than half the weight of the larger.
Stills versus video
Folks using motion-cams for research projects typically shoot stills (often in bursts) rather than video, for several reasons. Interpretation from video is perceived as more ‘subjective.’ It’s harder on battery-life, an important factor if cameras go unattended for months at a time. And it takes a lot more time to review and process hundreds and thousands of videos. If I had an array of 50 cameras across the landscape as friends on Tàan (POW) do, I’d have given up shooting video by now. My Bushnell camera-sets in open locations often ‘wind-trigger, giving me more critterless videos of branch-movement than actual movies of animals. Deleting these in batches of 10, based only on their opening-frame ‘poster,’ surely causes occasional lost critter-vids. (More expensive ReConyx models rarely false-trigger, justifying their price by reducing processing time that agencies—unlike us nature-hobbyists—must pay staff for.)
Basically, “science” needs to convert motion-cam images to some kind of number, for legitimate quantitative analysis. Video is just too qualitative and slippery.
But for study of animal behavior, jpgs miss a lot that video catches. Image quality is relatively poor on these cheap-sensor cameras whether you’re shooting stills or video. So you don’t sacrifice a lot by pulling your stills from video freezeframes, compared to say, setting the menu to 3-shot .jpg bursts. And video gives you the option to ‘slider’ over to exactly the pose you need. For example the big-&-little bear comparisons above. For extracting maximum story from your motion-cams, set em to video.
