For this final challenge of Session #4 we have something a little different—explain the scene shown in the photo below. Your answer can be as short and concise or long and narrative as you wish—points will be awarded subjectively depending on how closely your explanation agrees with reality. Standard challenge rules apply, including moderated comments during the challenge period (you don’t have to be first to score points), early-bird points to those who do arrive at the correct answer before others, etc., and as always, creativity and humor are encouraged. C’mon—we’re all natural historians here, aren’t we? Let’s hear some natural history!
Explain the scene in this photo.
Copyright © Ted C. MacRae 2011
Beetles In The Bush 
Well, I feel like ripples like that could be present in either an ocean beach or a river, but they would be more likely to be exposed on an ocean beach, plus this looks more like sand than a finer, riparian sediment. The footprints belong to some kind of passerine, based on that long hallux, and they seem to be walking with a narrow trail width rather than running like, say, a robin. They look too dainty to belong to crows, so I’m thinking some kind of icterids, like grackles or red-winged blackbirds, which would be moving through some parts of North American in numbers right now, so it would make sense to see a flock of them traveling together like this (three trails are visible, moving right to left). But wait, you’re probably not even interested in the bird tracks, this is probably about the holes (which the birds don’t seem interested in). Well, they’re certainly not larval tiger beetle holes, but they do look an awful lot like resting burrows of adult tiger beetles. That would be a pretty impressive density if that’s what they are. I suppose if I’d been paying attention to where you’ve been lately and knew of an intertidal cicindeline that lives there, I’d guess that that’s who made the holes.
I’ll give you 2 pts each for figuring out this is a sand habitat, that the holes are tiger beetle burrows, and that they were made by adults rather than larvae. I haven’t a clue about the tracks (though you among anybody would know) so I’m going to pass on awarding points for them.
Total = 6 pts
It’s a lovely sinuous scene in an aeolian dune field. Gimme shelter. The burrows are those of tiger beetles, many of which will burrow into the substrate when conditions become too extreme (too hot, too windy, too cloudy, too much like a Mountain Dew commercial). Perhaps Cicindela formosa cf. gibsoni? The vertebrate trackways are clearly derived theropod dinosaurs.
Nearly perfect, just missing the species – clearly you’ve been paying attention. 2 pts each for sand (er, aeolian), dune, adult, and tiger beetle, plus 4 for the correct genus. One other person matched your answers, so as a tie breaker you get a bonus point for being first.
Total = 13 pts and a lock on the overall victory.
p.s. I really wanted to award humor points for “derived theropod dinosaurs” but I think the other contestants are already crying “Uncle!”
Well, first of all, it’s a sand dune, with the prevailing wind from the left side of the picture. The ripples form due to the inherent instability of a sheet of wind-blown sand. Any slight imperfection in the surface causes the wind to slow enough that whatever sand it is carrying drops out, making a small mound of sand. This in turn makes another mound further downwind, and repeating this produces a series of ripples with a characteristic spacing depending on the wind speed. Coarse particles tend to accumulate at the crests of the ripples and help to stabilize them. Since the ripples get wiped out if the wind speed gets high enough to move the coarse particles, this shows that there has been at most moderate winds for at least the last few days.
Since prevailing winds are from the west in most of North America, I’d say that west is to the left, and from the shadows the sun is fairly low in the sky to the east. So, time was probably around mid-morning.
It looks like there was a gentle wind from the north overnight, partially filling in the mouths of the burrows in the sand. I expect that you were there hunting tiger beetles, so it is reasonable to think that these were tiger beetle burrows. The burrow openings will be more circular once the inhabitants have a chance to come to the surface and clean them out a bit.
There was obviously no wind in the early morning just before the picture was taken, because it would have wiped out the three trails made by something that was kind of bounding across the sand, making a little crater every time it touched down. From the teardrop shape of the craters, I think they were going from the lower right to the upper left. I’m not sure what they were. Since there were three of them all going the same way, I suspect they were something that you flushed out just before the picture was taken, as you approached from the lower right side. Maybe some sort of crickets? Or tiger beetles half-flying and half-jumping, keeping low to take advantage of the surface effect for efficient flight, while kicking off from the sand periodically for extra speed (and blowing out little craters with the downdraft from their wings every time they touched down)?
Clearly you love a mystery! Yes it’s a sand dune, and those are tiger beetle burrows, though not larval. Your reasoning on orientation was sound, but in fact the dune is facing south, so the photo was taken mid-afternoon (must be some swirl effect from the mountains just east of the site). I’m inclined to agree with others that the tracks are from birds, though I don’t know and am not awarding points for them.
Total = 6 pts (2 each for sand, dune, and tiger beetle).
Oh, and I think there is a dead insect (a beetle?) in the upper left. I can’t see it well enough to make out what kind. It doesn’t look like it has been dismembered and eaten, though, so I suspect it died of natural causes.
Perhaps – I didn’t even notice it at the time.
Okayyy… it looks like a shallow-sloping tidal sandy beach with ripples. If the colour is real, it’s quite pinkish, so a sandstone area? The little dark holes appear paired and so suggest U-shaped burrows, maybe something like Arenicola (lug-worm) or another arenicolid though I can’t see the usual faecal cast at one end – to be honest I don’t know which littoral species you get in North America. The other marks I imagine are the footprints of a wading bird feeding by probing in the sand. They don’t seem concentrated around the holes (more a linear feeding walk), so maybe seeking other invertebrates as arenicolids can be quite deeply buried in their burrows. OK, I think that’s about it.
Interesting line of reasoning for the U-shaped burrows, which would actually make good sense if this was a maritime and not dry land scene. I’ll give you 2 pts for figuring out it’s sand.
Wow, this is not at all what I was expecting for the final challenge in the session. Since this looks to be a sandy area, and you were recently in the sand dunes of Colorado, I’m going to say this photo was probably taken at the Great Sand Dunes National Park. The indentations in the sand look like bird tracks, and since the American avocet, Recurvirostra americana, is one of the birds featured on the NPS page about the park, I’ll go ahead and say that’s what created the tracks. As for the holes in the sand, I remember you said that while looking for Cicindela formosa gibsoni(Order–Coleoptera, Family–Carabidae) in the park, they began digging burrows before you could get any good field shots. In that case, these are the burrows they escaped into.
I like to change things up every now and then… Sand dunes, yes (4 pts). Cicindela tiger beetle adult burrows, yes (8 pts). Only the species (and state) are wrong.
By the way, you won’t find C. formosa gibsoni at Great Sand Dunes NP (or Idaho, where this photo was taken).
Total = 12 pts
Water runoff (in the depressions) has widened and more fully exposed the entrances to beetle burrows.
Wind rather than water shaped this landscape, but I’ll give you 3 pts for deducing beetle burrows.
Well, this certainly is going to be a wild guess. Based on the environment, I’d say that the slight furrows in the sand could be tiger beetle tracks. The tiny holes may be the very beinnings of burrows from 1st instar larvae, or even indentations made by the abdomen of the female tiger beetle after recently ovipositing. This is a wild guess, but I am almost certain the holes must be either borrows or indentations as a result of ovipositing. I can guess that the “tracks” belong to an insect or at least an arthropod of some kind. This is tricky…
Let’s see – sand (2 pts), tiger beetles (2 pts), burrows (2 pts). But adults and not larvae or oviposition holes.
Total = 6 pts
Ahh! Interesting challenge! It looks like a tiger habitat, so that explains why you were there. It looks like a snake went through the sand at one point. It also looks like there are bird tracks in the sand. It also looks like Tiger burrows are there as well! Perhaps a bird was trying to fish out some tiger larva when a snake came up from behind and snatched the bird away. Probably incorrect, but i’m going to stick with my summery. If not a bird, perhaps a rodent?
Sand, “tiger” (I’ll give you the benefit of the doubt that this means tiger beetle and not the much larger Bengali vertebrate :)), and burrow net you 2 pts each. I don’t know about the other tracks.
Total = 6 pts
Hmmm. I think the tapered, elongate tracks are from a large, pointy-butted tenebrionid starting and stopping, lowering the abdominal tip into the sand when it stops and pulliing it up as it starts off. Not sure what the rounder, deeper, paired impressions are from.
You know, I never even noticed the paired appearance of the burrows that showed up in this photo – it led a few of you astray but is purely coincidental.
You do net 2 pts for mentioning sand.
Pingback: ID Challenge #13 – Addendum « Beetles In The Bush
Pingback: ID Challenge #13 results and Session #4 final standings « Beetles In The Bush