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Len Kerry
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Posted: Wed May 5th, 2004 04:44 am |
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Hi Joe S, Mark K and group.
there has been very little activity on the group over the last month or so so I thought I'd ask for comments and discussion on an interesting topic I've been thinking about for some time. I recall reading (on this forum archive I think) someone asking about "resonant" appendages on bat houses to attract echolocating bats. As bats use a wide range of frequencies, I suspect a "resonant" structure would probably be hard to achieve and in any case, probably would not tend to return a strong echo by its very nature.
Taking the thought a step further however, because the access points to most bat houses tend to be on the the underside of the structure, the presence of the (roosting) cavities may not be obvious to a bat unless it is flying low or the bat has already decided to investigate the structure. Doing something to the side faces of a bat house to gain the bat's interest could encourage further investigation and ultimately lead to occupancy.
My thought is that there should be something on the sides of the house that gives a returning echo that simulates the presence of a suitably sized cavity (not a real one though for the usual reasons). Perhaps a real horizontal slot could be used but of insufficient height so as to avoid attracting flying insects occupying the house.
One thought was for a strip of material (the size and shape of a cavity that would interest a bat) that was much less reflective to echolocation signals than the structure of the house. It may look like a cavity at reasonable detection distances. However, many such materials are porous and would tend to get water logged. This may or may not be a problem!
Another thought was to use cavity shaped strips of glass. Although they would give a strong return echo from face-on, from a direction just above, below or to the sides the glass would reflect most of the the signal in another direction and the low return in the direction of the bat may cause it to resemble a cavity at a distance.
My last thought was to use strips of glass on the 90 degree faces of small sized quad shaped timber, the hypoteneuse of the quad being used to glue it to the side of the bat house. In this case, the echo reflection from face-on and from the sides would be very low making it look like a cavity , but from a 45 degree angle above or below there would be a strong reflection (however, a stonger return signal than the surrounding area may also get the bat's attention).
I'd like to see some discussion on these (and other) ideas. I think there is a lot of room for experiment to see if this sort of thing can help occupancy rates or at least lead to earlier occupation of houses.
The name of the game is to get the bat's attention!
Regards,
Len Kerry
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kent
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Posted: Thu May 6th, 2004 03:06 pm |
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Len,
Several years ago a friend and I were considering constructing a bat attracting device using an oscilloscope. I still think it would be an interesting idea and will probably put one together some time.
Anyway after studying bat house designs and doing a lot of experimenting with a variety of designs and locations , I have come to the conclusion location ,location is the key to bat house success.
When you study caves or bat hibernaculums that are closed , bats using that hibernaculum find a new cave sometimes with very small openings.
Possibly bats are using a scouts more than we realize. There are some bats that leave Bracken cave earlier, some people think these bats find area where corn ear worm moths are when migrating north. When the rest of the bats leave Bracken they go where the earleir bats are feeding.
A number of bat houses have vent slots in front and sides where bats echolocation could find the openings. Most of the time bat houses with no vent slots in sides or fronts are used first, even when houses are mounted back to back on same mounting post.
There is one bat house manufacturer that has the side slots in her bat houses advertised as , echolocating slots for bats to find houses . I do not know if her houses are any more successful.
I do maintain contact with bat house groups in this country , United Kingdom and Germany. If the slots in the bat houses were successful the info would be passed along.
The most successful bat houses are the houses placed along corridors or roadways near the tree canopies where bats feed.
I still think air movement in areas around bat houses has a lot to do with the occupancy rate of bat houses.
At one historic site where they had put up some large bat houses in an opening in a qpprox. 5 acres of trees. The houses never had bats in them .
I put up a number of houses along the edge of the trees , about 400 feet from the goup of houses in the clearing. The houses I put up on the edge of of the trees were all occupied the first summer, within weeks of being put up.
Also in a large ILL. state park placed some bat houses along the road edges these houses were occupied the first week. This park had another larger bat house of a different design that had been up a number of years. The new bat houses along the road had hundreds more bats in them .
One of the reasons bats use bridges to roost under could be because of the air movement. This is one of the reasons I want to use retired faltbed semi trailers placed across gullies with baffles under them for the bats.
Kent Borcherding
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Len Kerry
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Posted: Fri May 7th, 2004 12:12 am |
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Thanks for the reply Kent.
I agree that bats will find suitable roosting cavities when they have the need. However, the idea of gaining the attention of bats is a fascinating idea and may be worthy of further investigation, even if the outcome supports the conclusion you've already arrived at!
I'd still be interested in the thoughts, ideas and experiences of other group members on this issue!
Wrt air movement arround roosts, I read your most recent post on this topic a little while ago and based on the extensive reading I do on bat ecology, I think there may be something in what you say. It does seem that certain species of cave-entrance roosting bats do indeed rely on air-currents near the entrance of the cave to help provide the roosting microclimate they require. These entrance-roosting bats also tend to be the opportunistic ones that take advantage of mild spells in the winter months to go out foraging to build-up their fat reserves - it helps improve their chances of surviving the winter. Being near the cave entrance allows them to monitor the temperature of the air-currents and make a decision as to whether or not to to go out foraging!
Regards,
Len
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Joe Spencer
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Posted: Fri May 7th, 2004 02:33 pm |
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Great stuff here guys! Len with the rocket design you put up, I am actually experimenting with precisely that cavity signatures and alerts. I have always made most of my standard box style nursery bat houses with a front 1/2" vent for excessive heat dissipation and potential "Hey bats do you see this crack" exposure. I haven't put up enough non-vented bat houses near them for a side by side comparison. What makes this difficult is if the bats notice the bat house with the vent and decide to investigate they will most certainly see the other non-vented bat house beside it during a flyby. Also on your rocket design and some that I have built in the past, you have the nice STEP exposure on the bottom which doubles as a 360 degree landing pad as well as the lower horizontal vent. You would think all these things should be quite enticing or easily noticed by a bat which they probably are. But whether the bats will accept them or prefer them is a good question by Kent. The location location just does seem to make sense and of course this assumes the bat house is well designed as well. ALSO Len I would suspect that the rocket design you have (provided the crevices are not too large) will be less susceptible to PAPER wasps at least here in North AMerica where they are a problem in bat houses with larger crevices exceeding 3/4". Also when the crevices are 3/4" the WASPS build the nest at the butt end bottom of the partitions where the wasps are protected from rain etc. by the outside shell of the bat house. My reasoning is that with the exposed (elements) entrance on your current rocket design, WASPS might be less likely to build. Bats are more exposed this way though and not sure how this would effect the predator issue specifically birds of prey. So much remains to be tried.
Thank's 
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Len Kerry
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Posted: Wed May 12th, 2004 03:51 am |
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Thanks Joe.
If you come to some useful conclusions after your systematic experiments, I hope you'll post some results..
The cavity entrance slots at the bottom of my roosts are 18mm (0.71 inches) wide. The vent slots on the side faces are 12mm high.
As you say, one would hope that the stepped landing platforms at the base of the roosts would be attention-getters in addition to the side vent slots.
Len.
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Joe Spencer
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Posted: Thu May 13th, 2004 03:21 pm |
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| On one of my sites, at a State Park with lots of water I discovered 30 little brown bats in ONE bat house which was horribly built and maintained, which had a warped roof allowing heat to escape and was barely a foot tall and 10 inches wide. This lone bat house had bats because the bat house was mounted on the campers HOT Shower building providing warmth. A large pond was adjacent and the Large PARK Lake was only 1000 yards away. As Kent states and the Bat House Builder's Handbook confirms, bats just weigh everything ie proximity to food/water fly and possibly hibernacula among other things. Another thing little brown/myotis bats probably like about campsites is that they have the numerous small road clearings within the woods that bats probably use as their route and I have seen them do this while camping. These bats feed at a lower height than the Big Browns we have which spend more time at the tree top level in my observance.....
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Mark Kiser
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Posted: Wed May 26th, 2004 12:04 am |
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Good stuff Len, Kent, and Joe,
Ventilation slots probably help in letting bats know there is a hollow structure inside that is potentially worth investigating, yes. A fake cavity may not give the same signature indicating a hollow, but it would be worth testing.
Frank Bibin in Georgia reports than when he puts up a new bat house among his other occupied bat houses, free-tailed bats fly up to the bottom of the new house multiple times, back and forth, each night for a period of about 30 to 35 days before moving inside. It's like they are suspicious of the new house and want to make sure there's nothing dangerous inside.
Has anyone else witnessed something similar with a new roost?
An interesting anecdote that might be worth trying to get bats' attention:
someone in South America, Brazil I believe it was, once mentioned to me that several bats were attracted to a metallic foil pinwheel, a kid's toy, attached to the rail of his apartment balcony in a downtown urban area. When the wind blew the pinwheel, he said bats repeatedly came by to check out the sound or motion, or possibly both.
The foil pinwheel may have generated perhaps a noise or sound frequency of interest to the bats (species unknown), or maybe they just liked the flashy bright colors.
Anyone care to give it a try near their next new bat house? It could probably be taped easily to a pole or other nearby object.
Cheers,
Mark
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Len Kerry
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Posted: Wed May 26th, 2004 03:42 am |
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Mark, that's very interesting information about bats inspecting a roost for a period of time before making use of it. It's very reminiscent of the behavior we see in other animals (such as cats and dogs and humans) when they are entering a dark or unknown place. There's no reason to expect that bats would be any different in that respect!
The observation of bats being attracted to a spinning pin wheel also makes a lot of sense to me. Some species, such as Tadarida braziliensis (Mexican freetail bat) emit what are called CF or (nearly) constant frequency echolocation calls that are well suited to detecting the doppler frequency shifts (or glints as they're called) caused by the beating wings of flying insects. The doppler shifts (or glints) caused by a highly reflective spinning pin wheel probably simulate some of their regular insect prey.
As you point out, Mark, possible ultrasonic sounds emitted from the friction between the pin and the plastic wheel may also be a factor.
Thanks for passing on these interesting observations.
Len
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newbie
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Posted: Wed May 26th, 2004 05:27 pm |
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well, there appear to be several bats using my Simple Economy bat house; I put a screen on the ground underneath to catch any droppings but may be that the local ants have gotten to it before I've seen it
the pinwheel idea is interesting, and as it happens I have one that I picked up loose on the beach, so I may just stick it up nearby and see if that increases the population ...
turns out that the bat house is not getting as much sunlight as I had expected; neighbor's trees have grown considerably over the spring and now block direct sun for much of the morning, then the roof overhang blocks it for the rest of the day ...
I may try mounting another bat house on the exposed trunk of the big fir tree; that's the only thing on the lot that seems to be high enough to get full sun for any length of time, had not realized before just how shaded this area is, between fir trees and oak trees ... many of the big fir's branches came down in the big snow&wind storm this winter, there must be 30 or 40 feet of bare trunk ... and I can cut more branches off if necessary
____________________
"Candy"
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Joe Spencer
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Posted: Mon May 31st, 2004 04:11 am |
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| Great News Candy! Any way you can put a small elevated board or something beneath the bat house to catch a few guanos! Since bats often defecate prior to roost return it often gets stuck on the siding of the building just below the entrance. Have you seen any? Usually you do need a lot of bats for this to occur tho. :thumbup: Candy is this a Lone Bat house?
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