Slope aspect in relation to herp finds

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Rich in Reptiles
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Slope aspect in relation to herp finds

Post by Rich in Reptiles »

Hey Everyone!
I've had a question lingering in my mind for awhile about how slope aspect can impact the densities of a herp species (all of this pertaining to the Northern hemisphere). I think it's commonly known in the herper community that a lot of snakes prefer south and south/west facing slopes because of more desirable temperatures, hibernacula, and gestating conditions, etc. But i'm wondering if other herps have a preference for certain slope aspects- especially salamanders and fossorial species because of variation in soil conditions. A couple years ago i field herped quite often in one ~75 acre area because it was so close to my house. I found around 140 zigzags throughout the year, and what i came to notice was that they were more commonly seen on the south facing slopes. I found Eurycea as well, but they seemed to occur equally on both south and north-facing slopes wherever there was a seep or spring.

So, i'm wondering:
#1- In your herping experience, have you ever noticed a heavier concentration of a specific herp species on a south or north-facing slope?
#2- Are there any publications or literature out there pertaining to this subject?

These two photos were taken on the same day; both hills were on different sides of me as i walked a path. Difference in vegetation is obvious, but what about that which lies unseen?
south-facing slope
ImageSouth-facing slope by Bethany Avilla, on Flickr

north-facing slope
ImageNorth-facing slope by Bethany Avilla, on Flickr

I would be very interested to hear what you have to say about this topic!
-Bethany
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The Real Snake Man
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Re: Slope aspect in relation to herp finds

Post by The Real Snake Man »

If no one's done a study on this it would be an incredibly interesting thing to look into. Being from the flat land of the Rio Grande Delta, I have absolutely nothing to contribute, but I too am interested to see what others will say.

-Gene
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Kelly Mc
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Re: Slope aspect in relation to herp finds

Post by Kelly Mc »

Im not losing track of this thread - I have interest in slope aspect using it more often now in vivaria strategy, composing from 50 to 80% of the space value with various lizards and snakes and some small anuran species.

Really anticipating input, thanks for this great subject and the photos, Rich in Reptiles.
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chrish
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Re: Slope aspect in relation to herp finds

Post by chrish »

I have always heard at least in the north that south facing slopes produce more herps. We always used to tend to favor them when herping because we believed that. I have at least some anecdotal support for that hypothesis from West Texas in the spring, but then again that's where we looked most often.

I imagine as you move further south this effect would be less pronounced.
I do remember when peeling bark for scarlet kings (I know, I know - I was young and stupid :oops:) in South Carolina in March, we found the SKs on the north side of the tree more often than the south. We figured the south facing bark got too hot and too dry.

I wonder if there is any corresponding data for north facing slopes in the southern hemisphere?
I have only ever found two critters on any sort of "slope" in the southern hemisphere and both were on the north facing slope, so that's 100% support right there! ;)
MCHerper
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Re: Slope aspect in relation to herp finds

Post by MCHerper »

Funny that this topic came up, because a few times a similar question popped into my mind. I always trusted the wisdom that more herps were found on south facing slopes, and have found evidence to support it. The only species that I can think of that I believe to find more often on north facing slopes are P. glutinosis, however I haven't done a comparison.

Regarding this topic, I can't help but to wonder if there are differences in geologic features and erosion factors that shape south-facing areas and therefore make them more desirable. Winds typically move from west to east, mountains built on the East coast have steeper sides south and west because of the orogenies that formed them (continental collisions). Are there other factors such as differences in moisture-temperature gradients that make the south facing areas erode faster? When I look at a terrain map of the Mid-Atlantic, the steepest areas, for the most part, face southwest. Does this make for the geological features that support the gradients that herps seek, such as easier access to areas below frost line?

This is a great topic to bring up, and it's fascinating to me to find out more about the abiotic factors that shape preferred habitats.
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Kyle from Carolina
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Re: Slope aspect in relation to herp finds

Post by Kyle from Carolina »

There is certainly a fair bit of scientific literature on the subject. A quick search on google scholar brought up some stuff. One I noticed right away was:
Harper and Guynn 1999. Factors affecting salamander density and distribution within four forest types in the Southern Appalachian Mountains. Forest Ecology and Management. 114(2-3). doi:10.1016/S0378-1127(98)00355-7

In perusing the abstract I noticed that aspect was important for their study species and region.

It seems to be pretty common when describing landscape scale distributions of herps (and plants, etc) these days with easy access to spatial data and what not.

I would guess that moisture differences between aspects would be important for salamanders while temperature differences would be more important for hibernacula features in the northern hemisphere, although there are other important factors (type of soil, bedrock). South facing slopes generally have greater sun exposure. That being said, the biggest rattlesnake den in British Columbia is north facing. Also, in some areas that get a lot of snow, north aspects accumulate more snow cover (on average) and are better insulated against the cold air, meaning that the herps don't have to go as deep to reach the frostline. I'm thinking specifically of some northern Phrynosoma. The point being that there are a multitude of factors influencing distribution and abundance.

I'm curious to hear what others have to say.
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Re: Slope aspect in relation to herp finds

Post by hellihooks »

Here in So Cal... southern sunny slopes for reptiles... shady northern slopes for Sallies. (both Broad generalizations) logically... in the northern hemisphere, southern facing surfaces will get more sun, north facing surfaces, less sun= more moisture. Think of moss growing on the north sides of trees.

As for measuring slope gradient... i get fellow herpers to put thier foreheads to the ground... :lol: :lol: :lol: jim
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Rich in Reptiles
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Re: Slope aspect in relation to herp finds

Post by Rich in Reptiles »

Very interesting discussion going on! Thanks for everyone's input, i find it a very interesting topic.

Chrish- I've never even considered how a tree, while still standing, could provide thermoregulation for a snake under its bark! Fascinating!

Kyle- I actually see Dr. Harper every year through my 4-H wildlife judging competitions here in Tennessee!!! Knowing that he was one of the authors of that paper, i would love to ask him a few questions next time i see him! Thanks for posting that! For those interested, here's the link to the PDF file of the paper Kyle mentioned- http://www.srs.fs.usda.gov/pubs/ja/unca ... per002.pdf

I realize there could be a zillion different combinations of environmental factors which make it difficult to make a general statement such as "All Plethodon salamanders thrive better on north-facing slopes". There are just too many conditions, too many species, too many localities, etc. But it would be neat to know if there is a trend where a certain group of herps do better on one slope aspect or another, and why.
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Tim Borski
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Re: Slope aspect in relation to herp finds

Post by Tim Borski »

In my experience down here in far south FL, cover that stays dry underneath (more sunlight per day) shows me far more herps than cover that stays moist/shaded. But walking both areas after dark typically shows about a 50/50 average per cover. So I assume that the herps are in both conditions but are only readily accessible in one? 'Just thinking out loud down here...

Tim
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Kent VanSooy
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Re: Slope aspect in relation to herp finds

Post by Kent VanSooy »

In my SoCal experience, the beasties will move around depending on the season/conditions - south-facing slopes will be more productive early in the spring when it's not too hot and dry, but then we'll start finding animals later on the north-facing slopes. Sometimes the north slopes are the only ones worth checking. It could be too that it's movement from under cover to deep underground (and vice-versa) instead, but radiotelemetry studies show that many herps have substantial home ranges.
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Re: Slope aspect in relation to herp finds

Post by mfb »

A lot of good comments have been made on the slope issue, so I don't have anything to add. But while you are keeping track of this, you might also want to look at the types of trees you are finding them under. There was a neat paper published in Copeia in 2013 showing that Ambystoma laterale actively avoided the leaves of cherry trees. This was noticed in field surveys by a group of graduate students at the University of Michigan taking a field class. They found few salamanders in the cherry tree litter. They followed up with an experiment and found that the salamanders purposely moved out of cherry leaves.

Link to paper here:
Belasen et al. 2013 Copeia

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MCHerper
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Re: Slope aspect in relation to herp finds

Post by MCHerper »

That's interesting that you mention that mfb, I always wondered whether salamanders found any of the compounds in pine needles to be aversive? I have found A. opacum under pine bark and near pine needles, but I don't believe that I have found plethodons near pine needles. I realize that most pine trees grow in less forgiving, sandier soils which are drier, but they also seem to me to avoid adequately damp soil near pine plantations.
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Rich in Reptiles
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Re: Slope aspect in relation to herp finds

Post by Rich in Reptiles »

In the paper Kyle mentioned (pg. 7) it talks about how the soil and leaf litter pH is usually lower in coniferous stands and that because the litter layer is thinner it dries out more quickly than the litter layer of a hardwood forest would. So maybe acidity and lack of moisture is the issue there?
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Re: Slope aspect in relation to herp finds

Post by simus343 »

From my experience in NW Florida I see most of my salamanders on relatively flat ground. While in steppes, I have found Eurycea bislineata on slopes facing every direction. The only species I have found facing a specific direction has been Pseudotriton ruber, and they have been on east facing slopes in steephead ravines and east facing hills leading towards steephead ravines.
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mfb
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Re: Slope aspect in relation to herp finds

Post by mfb »

Hi MCHerper,

That would be very interesting to know about pine needles. Off the top of my head, I don't know any studies that separate the effects of pine needle chemical compounds from the types of soils pines grow in. However, there has been some studies that have shown chemical compounds in invasive plants have negative effects on amphibian larvae. Seems like an area worth more investigation.

Mike
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Bryan Hamilton
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Re: Slope aspect in relation to herp finds

Post by Bryan Hamilton »

Its an interesting question, one I've spent quite a bit of time working on. I would say that some of the highest snakes densities in North America preferentially occur on south facing slopes. As someone else noted, there is substantial geographic variation. Aspect is an important factor but its value varies with time and space.

The mechanism of aspect selection is also pretty poorly understood. The paper linking habitat selection to leaf substrate is a pretty nice example of a way to get at mechanism.

I'll shamelessly plug my own paper. If anyone wants a pdf feel free to pm your e-mail address to me.

Hamilton, B.T., Nowak, E.M., 2009. Relationships between Insolation and Rattlesnake Hibernacula. Western North American Naturalist 69, 319-328.
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walk-about
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Re: Slope aspect in relation to herp finds

Post by walk-about »

That is a great paper Bryan. Lots of good points being made here and it really is interesting to take in eveyone's feedback to Bethany's excellent post. I have many of my own theories on this subject and will add them later when I have more time to articulate them into text. Great thread guys.

Dave
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Re: Slope aspect in relation to herp finds

Post by Craig »

Very interesting subject. Certainly many, many variables involved. As a geologist, I can relate to the effects of varying rock and soil types on biodiversity.

As some have noted above, when comparing slope biodiversity and habitats, one needs to be mindful of geography. That is, habitat biodiversity on slopes in Tennessee would likely be quite a bit different than that in New Mexico, British Columbia or Colorado simply due to differences in climate for example. However analysis of diversity within the same climate area for different slopes would be quite interesting.
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Kelly Mc
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Re: Slope aspect in relation to herp finds

Post by Kelly Mc »

Craig wrote:Very interesting subject. Certainly many, many variables involved. As a geologist, I can relate to the effects of varying rock and soil types on biodiversity.

As some have noted above, when comparing slope biodiversity and habitats, one needs to be mindful of geography. That is, habitat biodiversity on slopes in Tennessee would likely be quite a bit different than that in New Mexico, British Columbia or Colorado simply due to differences in climate for example. However analysis of diversity within the same climate area for different slopes would be quite interesting.

Your perspective as a geologist in relation to this, and the taste of which is hinted at above is intriguing and that's putting it far too mildly, I almost got chills. Exciting stuff sure hope you post more
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Re: Slope aspect in relation to herp finds

Post by chris_mcmartin »

There may be tie-ins to vegetation type found on north- or south-facing slopes which contributes to the likelihood of finding herp species there. Here in Kansas, a friend has been researching red-bellied snakes (Storeria occipitomaculata) for a number of years, and recently has begun exploring the correlation between what it eats (snails and slugs), what the prey eats (leaf litter from certain trees), and what those particular trees need (certain levels of calcium in the soil). Some areas have more of this calcium available than others, therefore more of those trees, therefore more of those gastropods, and that may serve as a predictor of where the snakes might be found. I'm only roughly synopsizing the research here but I find it fascinating and am interested in applying a similar concept (predicting a particular species' occurrence based on several connected nodes along the food web) to other species in other regions.
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Rich in Reptiles
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Re: Slope aspect in relation to herp finds

Post by Rich in Reptiles »

I'm excited to see so many great thought-provoking responses!

Always good to see you on here Dave, I look forward to reading what you have to say about this topic!
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Re: Slope aspect in relation to herp finds

Post by HerpMan ATL »

Very interesting topic. I'll be watching this one.
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Brandon D
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Re: Slope aspect in relation to herp finds

Post by Brandon D »

I have read in many books that snakes prefer south and southwest facing hillsides. I mainly focus on milk snakes and literature over and over says that they prefer these areas. Now a lot of this literature was from many years ago or stemming from literature that was from many years ago in a not so drought infested world. I have personally found milk snakes on north facing hillsides in the same numbers as south facing hillsides. But in some locations I have never found them on the north slopes and only the southern slopes. why I don't know, possibly has something to do with the subterranean habitat and occupants, also in areas where moisture holds better on the north sides may be the reason they are abundant there. I do focus on south and south west slopes and I have to say some areas it holds true, but other areas prove that it is no law.
heres some lampropeltis for the fun of it

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Re: Slope aspect in relation to herp finds

Post by Jeroen Speybroeck »

Nice topic!

Let me add some European perspective about perhaps a larger scale way to look at the same problem. I don't remember exactly where (but could/should dig it up, I do remember the author is Rudolf Malkmus), but a study has been done about altitudinal distribution of reptile species in a mountain range in Portugal.

If I remember well, it showed that ...
(1) species richness is highest at lower elevations on the southern slope,
(2) the same species "lives lower" on the northern slope than on the southern slope,
(3) certain species (= some endemic amphibians + species with a distributional center of gravity further north) are virtually absent from the southern slope.

I might have introduced some personal assumptions into what I think I remember, though.

From my own experience, I'd say it's obvious that reptile species richness and abundance (or beter: the biased impression of those variables that you get when herping) are generally higher on warmer slopes, while for amphibians it's more complicated (as certain species are specifically adapted to using waterbodies in warm environments).
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Re: Slope aspect in relation to herp finds

Post by krismunk »

Edit: Disregard below comment. Quoted text has since been fixed :)
Jeroen Speybroeck wrote: (2) the same species "lives higher" on the northern slope than on the southern slope
Really?

That sounds counter intuitive to say the least.
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Kelly Mc
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Re: Slope aspect in relation to herp finds

Post by Kelly Mc »

It does but I could see how that would be, temp readings on these aspects and other specs of course would be interesting
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Re: Slope aspect in relation to herp finds

Post by chris_mcmartin »

He edited it to say "lower." :thumb:
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Kelly Mc
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Re: Slope aspect in relation to herp finds

Post by Kelly Mc »

Ok. How I thought about it was Not at Warmest on the Southern, and not at Coolest on the Northern. (?)

But it could be exposing a deficit I have in comprehension of some things, which also exposes itself per calendars and also pull a blank at the juxtaposition of odd and even numbers. :(

I wonder if anyone also uses a radiometer when herping, it would be a good addition to piecing together the dynamics of this and other habitat/herp dynamics.
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Jeroen Speybroeck
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Re: Slope aspect in relation to herp finds

Post by Jeroen Speybroeck »

krismunk wrote:
Jeroen Speybroeck wrote:(2) the same species "lives higher" on the northern slope than on the southern slope
Really?
That sounds counter intuitive to say the least.
As noted, I obviously made a mistake, which I now correct. I asked krismunk to delete his post to avoid confusion, but that's apparently not possible + came too late. Apologies.
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Re: Slope aspect in relation to herp finds

Post by Coluber Constrictor »

.
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Kelly Mc
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Re: Slope aspect in relation to herp finds

Post by Kelly Mc »

Kelly Mc wrote: radiometer when herping
UV radiometer
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Jeroen Speybroeck
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Re: Slope aspect in relation to herp finds

Post by Jeroen Speybroeck »

Coluber Constrictor wrote:I live in a pretty flat area, so I rarely think about slopes at all. But come to think of it, one of my favorite herping spots is on a little oak ridge facing south over a wetland. I have had the best luck there in May late in the day when it is quite hot (80 F or so), and I am thinking the abundance of snakes has less to do with the fact that it is a south facing slope, and more to do with the fact that it is wetland/dryland edge habitat. That and the abundance of prey (tons of frogs and lizards).
Being a flatlander myself, I would say "micro-slopes" are very important in cooler climates. Some snake populations around here clearly crowd on small ridges. Cold-blooded prey aggregating in these places can only enhance that effect, I'd imagine.
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Re: Slope aspect in relation to herp finds

Post by mfb »

One other thing to keep in mind is to separate whether slope affects density vs. "catchability" of salamanders or other herps. There might be similar numbers of salamanders on North vs. South slopes, but they may be deeper in the ground or otherwise harder to find on one slope vs the other.
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Kelly Mc
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Re: Slope aspect in relation to herp finds

Post by Kelly Mc »

mfb wrote:One other thing to keep in mind is to separate whether slope affects density vs. "catchability" of salamanders or other herps. There might be similar numbers of salamanders on North vs. South slopes, but they may be deeper in the ground or otherwise harder to find on one slope vs the other.


Thats such a cool point. The limber perspective to consider what we dont see.
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walk-about
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Re: Slope aspect in relation to herp finds

Post by walk-about »

Typically it seems here in Kentucky & Tennessee, that there is usually more canopy on the north slopes while south slope more open. Bethany's pics reflect this. You'll notice what I could identify as a least one American beech, yellow tulip trees and perhaps elms with the underforest of ferns - either Christmas/maidenhair...and these are often common along north slopes in upper south; This verses her south slope with what looks like at least one shagbark hickory, oak, red maples, and lacking virtually any ferns.

Alkalinity vs acidity often as with deciduous and coniferous communities has as much to do with geology and soil types found within those areas. Lizards it seems almost always favor more open areas - and these are typically south sloped to much degree. And this would apply to most snakes, especially snakes that predate upon said lizards and their eggs. Even our fossorial eastern Ringneck and Redbelly snakes, at least here in KY/TN prefer those more open areas and these are typically south sloped; while utilizing the more damp and moisture retentive micro-habitats of said slopes. As for regional turtles, more than 12 species are aquatic to a great degree and would not factor so much into this conversation, with the exception of the ubiquitous E. Box...the nomad of all turtles. And this specie will migrate seasonally where the food is. Whether it be mayfly & cicada spawns, blackberry season or sprouting fungi - they move within their home ranges throughout those seasons. Salamanders I typically find more so on south slopes than north, even Zags and Slimers - with the latter often migrating in the fall to more open areas under logs - but again, I find them in fairly open areas of forest with not so much canopy during this time. Anyways, some random observations here.

Rock ON!

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Kelly Mc
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Re: Slope aspect in relation to herp finds

Post by Kelly Mc »

Slopes in all their varieties, soils, ph, moisture and light realities, flora and rock types hint to having common denominators that are compelling to think about. The herps that live there are effortlessly incorperative of these in their behaviors.

We are perhaps one of the least adept organisms to navigate on a steep slope. But the most obvious physical law of a slope would affect the stealth of almost any larger animal/predator. This makes slopes excellent habitat but whether it is inadvertent benefit is a mystery to me.


I watch captives in vivaria navigate in slope aspect and it is different than in level scenario. But the space must be large or it doesnt produce the dynamic.
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Re: Slope aspect in relation to herp finds

Post by kit fox »

During the hot dry summer, in Castaic California, I saw hundreds of lizards on South and East Facing slopes during the morning. I saw three Southern Pacific Rattlesnakes on North or West facing slopes. All the Desert species I documented were in flatland areas.
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