Bat House Forum

[lakefly]

Joe,
Good questions, I was wondering about temperatures affecting the bats.
  
what has been the average daily high temp for the last week or two at your location or during the times when you found the most dead bats?  It has been about average with night temps in the 50's to 60's and daytime highs in the 70's and low 80's.  Pretty typical for the area.  I don't think there is a correlation to number of dead bats but will need to pay closer attention.

Does the home have a black or very dark shingled roof? Yes, dark grey shingles.

Has it been sunny or overcast during these days?  Mainly overcast with periodic sun.

Have you noticed increased bat activity near the soffits (lowest and coolest point) during the warmest time of the day?  It may be too warm for the bats although little browns do have a higher heat tolerance than other common species.  No, this is something that I have tried to watch.  I generally find the dead bats in the morning and few additional through the day - but again mainly in the morning hours.  For example; at about 5:30 I found one dead bat (young) and just now found another adult that had dropped.  Through the day I often see a few bats hanging just below the soffitt and generally they will move in and out of the soffitt through the day or drop dead or dying to the ground below.

I keep trying to make sense of this phenomenon and find links to something environmental but to date I just haven't found anything that seems to make sense.  It is very helpful to have people continue to ask questions - hopefully, something will  come to light that will help explain what is happening.

[Bat World NOVA]

Who's doing the diagnostic work on the bats? Do you know? It's entirely possible that they're feeding on insects that have very high levels of insecticides. Pesticides bioaccumulate, so you wouldn't necessarily see mortality right away. Some classes of insecticides have been shown to interfere with hormones and metabolism, which results in a slow decline. Do you know if any mosquito abatement programs are ongoing nearby?

Little browns feed heavily on aquatic insects (the flighted forms!) so they may be particularly vulnerable if wet areas are being treated. The weakening and dehydration are alarming and have been observed in rehab bats that have been exposed to pesticides.

As you probably already know, rabies does not appear to go epidemic within colonies and little browns seem to have lower incidences of rabies than other species, so I doubt it's rabies related. However, we really don't know a lot about bat diseases.

As an aside, I run a UV lamp in my flight cage to draw in insects--I'm not seeing the numbers of moths and smaller beetles I should be seeing. I think there are problems in the prey base for insectivores.

Leslie Sturges

Bat World NOVA

[Joe Spencer]

Lakefly, based on your feedback, this does not seem indicative of over heating.  Good info and questions from Leslie which should be persued.  That DNR information is crucially helpful.  Your site may prove to be invaluable once the data is analyzed and finalized if the latter is even possible.  Thanks again.... 

[lakefly]

    Leslie, Here are some answers:
Who's doing the diagnostic work on the bats?
The bats are being examined today by the National Wildlife Health Center in Madison, WI.  They have requested that I continue to collect and date the dead bats if further investigation is needed.  I don't know when they will have any results.
 Do you know if any mosquito abatement programs are ongoing nearby?
None to my knowledge but that is very limited about such programs.

Little browns feed heavily on aquatic insects (the flighted forms!) so they may be particularly vulnerable if wet areas are being treated. The weakening and dehydration are alarming and have been observed in rehab bats that have been exposed to pesticides.  Interesting - I imagine that this would appear through the necropsy results.

As you probably already know, rabies does not appear to go epidemic within colonies and little browns seem to have lower incidences of rabies than other species, so I doubt it's rabies related. However, we really don't know a lot about bat diseases.

As an aside, I run a UV lamp in my flight cage to draw in insects--I'm not seeing the numbers of moths and smaller beetles I should be seeing. I think there are problems in the prey base for insectivores.
Living on the lake we have an abundance of gnats, flies, mosquitos, etc so I have a hard time believing that food access is an issue.  I will say, however, that we have very few spiders this year - perhaps due to the bats or other factors.  To my knowledge there has not been any spraying in the area for insects (home spraying) and we do not spray.

It is great to continue to learn more from everyone's feedback!  

[Dave Miller]

Does anyone have a list of reasons that bats become dehydrated this time of year?

I don't, but I would guess that a list might look like:

• Not enough intake of fluids
• It sounds like their water source (the lake) is intact, so I doubt this is an issue.  But could there be something happening with the lake water (algae bloom or something?)  Has a new night predator moved in which is keeping the bats away from water?
• Did the bats get dehydrated over the winter?  An article I was just reading states "Many bats have visible damage to their wings, including scar tissue, tears and holes, apparently caused by dehydration during hibernation".  You might check the dead bats for these symptoms.  Here is the article from the Nashua Telegraph: Disease taking a toll on state's bat population
• Gastrointestinal illness.  I know in humans, diseases that cause diarrhea can lead to dehydration and death.  Do the bat's droppings look normal?

[Mulator]

The one thought that keeps coming to mind is the avoidance or limitation of water intake (resulting in dehydration) due to insecticides/crop/contamination of water source.

Interesting.  Have there been any updates?