Michigan Trappin,
There will be a myriad of angles folks might approach this from all I can do is speak on a few and why I do what I do, leave the rest to others to color in. I will say though you have some excellent bat excluder companies in MI that would
be good to talk to as with bats, where you live in relation to seasons and seasonality will differ as it can with various bat species.
So first a point of clarifying the way I look at when I can begin the process and put up one way valves or systems to exclude bats (or allow them to self evict as it may be called by some).
Most of our industry discussion over bat exclusion and timing often talks most about maternity season and not excluding while pups are being born and aren't volant (flying) yet.
There have been more and more discussions however among not only industry colleagues but among those in state and federal agencies and other conservation non profit groups related to bats about
winter and issues with winter exclusion or work.
In terms of the scenarios if we assume there aren't any bats within a structure, say it is a super simple (they never are, or maybe .5 of 1% of the time), you were there in the fall and the bats were easily seen in the
open rafters of this attic, no place else to hide (again hardly ever happens) and you end up getting the call to do the work or they accept your bid right about now. You go out, find no bats on site so you simply exclude
done deal and you get paid and go home, bats return later find the building excluded and go find another suitable roost.
Normally however our scenarios involve structures where you can't see every nook and cranny, inside every wall void, behind certain materials and therefore we anticipate there might be bats who either overwintered
in the structure, or have arrived with some early warm ups that may be inside the structure. Now we start looking at the idea of timing, why it may be important, and what the arguments are on this point.
I'll also state that information in terms of true hard facts are lacking on what happens if you lock out bats (evict through one ways during an exclusion) during a time of year when night temperatures are below a certain
range where bats are likely to survive and find another roost, despite that lack of information, there are some thoughts on when it wise and when is likely or possibly going to cause harm, each operator unless bound by law
or following law or policies in their state ultimately decides when to do this and when not to with various motivations from pushy client, to needing payment, to feeling like it is okay are all at play here.
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So, I just looked at a church who accepted my bid a month back. I've had nothing but nice daytime weather here and our winter has been super mild. So I went out to do a quick inspection of the attic and structure and just
verify if any bats did indeed remain overwinter in this structure or arrive early.
I found about 50+ scattered in this structure that later houses well over 3,000 bats of 3 different species and the day was sunny, nice, 70's, so talked to the management about coming back the next day to start exclusion and setup
one ways as the process worked along through the week.
Went home, decided I should check the temps for nights and saw that this area was going to be dropping more than 50% of the next 14 days into the 28-35 degree range. Decided to halt my actions until the temps get solidly above
45 and let the management know we'd be delayed until this date to assure the best outcome for evicted bats. This relates for me to food (flying insects) and ability to find alternate shelter of a similar quality. Others may not support this
or may have their own reasoning for why to proceed or why not, in this field like any there are plenty of opinions and you can decide for yourself in most cases what you want to do unless again bound by law or policy in your state.
Could I have put up the one ways after the 99% seal out? Yes of course I could have mechanically done so.
Would I know the outcome for the bats that exited on any of the colder nights in the early evening to drink and feed and return to shelter before the temps dropped into the sub freezing range? Nope, not at all and sometimes for folks
ignorance is bliss, but I prefer being motivated to provide not only the best service to my client, but to also conserve the bat colony, to not take these steps when I can see potential issues.
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In terms of what Josh shared which is worth discussing, the idea I'm assuming is that by leaving valves in all winter through April when bats are more active, you'd allow them to leave when they finally emerge for spring. I'm not positive
until he responds, but the theory would be bats do not wake up and go out at all during winter and sleep straight through without ever needing to leave the structure, or that if they leave they will find another place to roost and make it through the
winter.
If I put up valves during winter, I would worry as bats are documented to move from cave to cave during hibernation (winter) and also to exit caves, fly around and return to the same. If I have one ways up and the house is sealed and they do
leave on an excursion to return hours later unable to re enter, I've now forced them into a tough scenario unless they truly know of a similar structure with similar insulation and thermal properties.
I work in the mountains and I've learned that often bats are still around long after the snow starts to fly. I have to time my exclusion work in these areas especially to assure I've completed all one way work to evict well before the temps drop too low, otherwise I have to do the 99% seal and leave the other exit/entry points open so they can come and go as needed to avoid evicting them during weather that isn't going to support them.
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Bats are highly plastic in their ability to modify their use of space and modify their daily torpor bouts and even switch hibernacula if another is close by (caves have shown this in research). That however doesn't make me feel good about evicting an animal who eats food that is usually dead after the first killing frost and to leave them to try to acquire another solid place to spend the winter. Bats show incredibly high affinity for roosts be it maternity season, or hibernation and times in between.
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So to summarize my thoughts for you from my perspective on this, I use my best judgement in terms of nighttime temperatures when food (insects) become available and thermal conditions won't likely leave bats without ability to find a similar quality location to time my exclusion valve placement and sealing work.
This year I was ahead of the season and slowing down and looking at the temps made me realize I was about to rush an exclusion, when I could instead just postpone a couple of weeks and watch the temps warm to a reasonable overnight range.
I have clients who have been calling since our day temps went into the 60's and 70's over a month ago wanting to know when I would start. What they don't look at it is the nighttime temps, just the nice warm days. They also don't understand sealants and curing and those important aspects of the exclusion process which also relate to this.
Anyway, I hope this was helpful in some way, I've taken notes and points from many on this forum who have decades doing this kind of work. Some do the 99% seal and don't put up one ways till spring and they came to this on their own not by anyone
forcing them to do it, they thought it was best and I really appreciate knowing that and knowing them for all this shared info.
My advice is don't rush, check your temps, talk to some colleagues in state with more years of experience and anything else you can glean information from. In the long run bat exclusion like other things we all do is a learning experience, every job, every day, all the time, learning and adapting.
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I'll add that there is a concern and you could see policies coming eventually tied to laws about exclusion during winter months as folks are worried in the face of declining bat populations in the eastern half of the U.S. and Canada that bats overwintering in attics may be evicted and die off due to failure to wait or use a reasonable procedure. Just fyi, have heard dozens and dozens of discussions about this over the last few years and it gets louder each year in terms of concern.
The acceptable management practices for NWCO's does touch on winter exclusion as a subject you can find the info in this link as well as other things related to timing and practices.
https://www.whitenosesyndrome.org/sites/default/files/resource/wns_nwco_amp_1_april_2015_0.pdfBest,
Justin
