A backyard oasis for wildlife uses native plants and other features like water or feeders to provide the things wildlife need from their habitats. Click here to learn more about this backyard scene or download our article on Attracting Birds to your Yard.
Attracting wildlife to the backyard is easy by providing what they need: Habitat. Habitat is made up of four factors: 1) food, 2) water, 3) shelter, and 4) space. Each factor is essential for a good habitat and varies somewhat by the species of wildlife and the season. To ensure the greatest variety of wildlife species, provide a yard with the largest variety of food, shelter, and cover by providing different types of plants, feeders, and houses.
Natural sources of food can be things such as nectar-bearing flowers, seeds, fruits, berries, and insects. Planting a variety of herbaceous plants, shrubs, and trees provides a variety of species and a variety of structure. This ensures a wide variety of insects and other food sources.
For pulling wildlife in close for observation, you may want to provide supplemental feeding, especially in the winter months. Different types of feeders at different levels and locations, stocked with different types of foods (sugar water and insect larvae in the summer, for example) attract the widest variety of species. Check out our Feeding Wildlife page for more information on attracting wildlife with feeders.
All animals need shelter for cover, roosting, and raising you. Some species need more specialized cover than others. Plant trees and bushes for nesting birds, and add evergreen trees for protection against winter storms and winds. Standing dead and downed logs are important for over 50 species of Iowa wildlife. If they are not available on your property, you can provide constructed housing for many species. Check the designs available in this PDF file called Shelves, houses, and feeders for birds and mammals.
A source of water is essential for birds year round. Other animals are often attracted to it as well. Options range from a simple plastic bird bath to a rubber-lined backyard pond, complete with a recirculating pump to provide moving water. During the winter, a bird bath with a heater will keep the water from freezing and attract some birds that will not normally visit your feeders.
More Resources from ISU Extension and Outreach
- Attracting Birds to Your Yard - An article from wildlife extension specialists at Iowa State with more details on attracting birds to your yard.
- Gardening for Butterflies and Pollinators - A detailed article from extension entomologists at Iowa State about simple steps to help pollinators like butterflies and bees in your landscaping and gardens.
- Introduction to Iowa Native Prairie Plants - Learn about native plants from Iowa's prairies, many of which make for beautiful landscape plants to attract birds, insects, and other wildlife to your backyard.
- References and Resources for Prairies and Native Plantings - This general article from Iowa State Extension and Outreach provides lots of details about Iowa's native prairie plants that are great for wildlife in landscaping or in larger prairie plantings.
- Prairies and Native Plantings as Outdoor Classrooms - Maybe you don't want to welcome local school groups to your backyard, but you can find many relevant resources in this guide about promoting native prairie plants in small patches or in landscaping around your house.
- Rain Gardens: Filtering and Recycling Rain Water - Rain gardens are good for the environment and, when planted with the right native plants, can be great for wildlife too. Find out more information and resources on building your own rain garden in this publication.
- Visit the Garden for Wildlife page from the National Wildlife Federation, a wonderful resource with detailed information about making your yard and garden more hospitable for wildlife.
- Landscape Plants and Attract Birds - An article from Wisconsin that has a nice table of plants that provide habitat for wildlife throughout the year.
Food is one important element in wildlife habitat. But it's not the only element. Providing food sources is only one step in attracting wildlife and before you start to plant or supplement food, think about what other resources your land is offering wildlife. Is there shelter like shrubby cover or flowers and grass? Is there water? Is it safe? If you can say yes to these questions, you're ready to start thinking about food to attract more wildlife. If the answer was no, focus on the habitat first, then provide the food. Check out our pages for farmers or homeowners for more information about habitat.
Focus on Plants First
The best way to feed wildlife is to allow nature to do it. By this, we mean planting things that can consistently provide quality food sources year after year, like perennial flowers, grasses, shrubs and vines. Plants that produce seeds, fruits, or nuts can provide high-quality food through the year and year-after-year. Check out our landscaping page for more information on planting quality wildlife habitat in your backyard.
Providing Supplemental Food
If you want to concentrate wildlife or attract a wider variety of wildlife, you may be able to provide supplemental food, such as bird feeders. We describe some considerations to make when choosing foods in our article on Attracting Birds to Your Yard. You can get more tips and tricks from the article titled Bird feeding: tips for beginners and veterans. Also consider the best practices and understand the risks outlined here below.
Tips and tricks for winter bird feeding
This video from Iowa Outdoors covers the elements of winter bird feeding with Iowa State University Ornithologist Dr. Steve Dinsmore.
Risks with feeding and recommendations for safe feeding practices
Artificial feeding with feeders or bait piles artificially concentrates wildlife and increases the risk of disease transmission. Check out this video on research from Iowa State about disease transmission and birds to understand the risk and hear how to keep birds safe. There is substantial concern among wildlife biologists about the risks of transmitting Chronic Wasting Disease in white-tailed deer in some parts of the state and country by concentrating deer on artificial food or mineral sources. Therefore, we recommend never feeding deer or providing mineral supplementation, and removing bait intended for other animals, such as bird feeders, when deer begin to congregate around them.
Moldy grains, like corn or other seeds, can build up toxins and become problematic for wildlife feeding on them. Read this fact sheet from Oklahoma State on the issue and be sure to keep your food dry and free of mold. A build-up of these toxins in the food could do more harm than good for wildlife feeding extensively on the supplemental food.
Attracting and concentrating wildlife at an artificial food sources (like a food plot or feeder) can make for 'easy pickings' for predators. Here again, if the wildlife feeding at your feeders are at increased risk for predation, the feeders may be doing more harm than good so make sure you provide other habitat or escape cover around the feeders for wildlife to escape to when a predator shows up.
Be sure the food you are offering is high-quality and digestible. Studies on white-tailed deer in northern Great Lakes states have shown that deer can die of starvation with stomachs full of alfalfa hay in the middle of winter. In this case, the food provided was not digestible by the deer because they were accustomed to a different diet. Although this is an extreme case, it's important to remember the different needs of wildlife through the year and to focus on providing the right foods. In general, animals need high-protein foods during the spring and summer breeding seasons and need fatty foods during the cold fall and winter months.
Follow these simple tips to make sure you're doing the right thing for wildlife visiting your feeders.
- Plant a diversity of food-producing plants in addition to feeding to provide cover and reliable annual food sources.
- Clean any feeders that animals come in direct contact with to reduce disease transmission.
- Keep foods dry and discard any moist, moldy foods.
- Provide food in close proximity to other resources, like shrubby cover, to protect feeding wildlife from predators and inclement weather.
- Provide the right types of foods during the right time of year. For birds, focus on seeds and suet during fall and winter and sugar water and fruits during spring and summer.
- Never feed white-tailed deer to avoid risks of transmitting diseases like Chronic Wasting Disease.
Choosing the right foods for feeders
Many different food and feeder types are available and you can expect to see different species of birds on different types of feeders or throughout the year. Here's a table that highlights the main species of birds you may expect to see on the best types of food to offer. Avoid common bird food fillers like sorghum, wheat, or corn in favors of these offerings. Some of the best foods may be hiding in plain sight in your pantry like old peanut butter or a boiled solution of 4-parts water 1-part sugar.
Add water too
A diversity of birds can be attracted to a cool, clean water source. Be sure to keep it moving or fresh to avoid stagnant pools where mosquitoes may breed. Artificial sources of fresh water like bird baths or fountains are a nice accent to landscapes or really creative homeowners could build small ponds, rain gardens, or wetlands in the backyard to provide natural vegetation and water sources.
Every winter, after the snow melts and our brown, dormant grasses see the sun for the first time, we often find evidence of the busy lives of the meadow vole. While we were snuggled warmly indoors during the long winter, these mouse-sized creatures were actively feeding on seeds and vegetation and building an intricate trial system under the blanket of snow to stay alive and warm.
The meadow vole is a small, chestnut brown rodent that is seldom seen but very common all over Iowa. The tunnels it makes beneath the snow are, in fact, lined with thatch from last year's grass, giving them added insulation and perhaps some protection from the many hawks, owls, foxes, and other predators that feed on them. Voles have longish fur that almost hides their small ears and eyes. Their tail is short, usually no more than an inch, about a third the length of their body. Their legs are also short but they move quickly. About all we ever see of them is a brown blur beneath our feet as we walk through an Iowa meadow or prairie.
Since they serve as food for so many predators, they need to be prolific and produce a lot of young. Voles are sexually mature at about 32 days of age and, with sufficient food supplies, can breed year-round. With several litters per year, populations can build quickly. Localized vole population "irruptions" are not uncommon. Just as quickly, however, local populations may practically disappear. Populations of voles are highly variable from place to place and season to season.
Voles eat a variety of plants, especially grasses and wildflowers or forbs. In late summer and fall, they gather and store seeds, tubers, and bulbs. They also eat the bark of young woody plants and, when populations are high, can eat food crops, especially small grains, and destroy alfalfa fields. Unlike other mice, they almost never enter houses. They may be mistaken, however, for another small mammal that does get into houses: the short-tailed shrew. Though they may look the same, they are not even cousins. The shrew is an insect-eating mammal, a close relative of the common mole.
The runway evidence of voles' presence is most obvious in the early spring as snow cover disappears. However, close inspection of grassy areas during the growing season may also reveal less obvious runways in the turf, sometimes including the top 2-3 inches of soil. There are often numerous entrances to this runway system and the vegetation is often closely clipped or dead in well-travelled runways. The runways are 1-2 inches in diameter and typical mouse feces may be found in them.
In addition to damage to turf, voles most often injure, weaken, and/or kill young trees and shrubs by gnawing at the bark and often girdling them completely. This most often occurs in the fall and winter but is not obvious until the spring. The plant may partially leaf out and then suddenly wilt and die. Close inspection of the base of the plant will reveal girdling of the bark at or near the soil surface. Other chew marks at various angles up to 2-3 inches above the surface also indicate vole damage.
As with most wildlife damage management, a combination of techniques leads to the most effective program:
Reduce cover by mowing. In turf areas, including lawns, golf courses, orchards, and parks, vole populations can be kept to a minimum through regular mowing. Though the grass tunnel systems are evident in the spring in many turf areas, as soon as mowing begins, the animals must retreat to areas of deeper grass in order to survive. Mowing exposes them to heavy predation. Occasional mowing in areas adjacent to turf areas will also reduce cover and expose them to predation. This is recommended, however, only in areas of high vole populations.
Exclude voles from around trees and shrubs by installing 1/4-inch mesh wire cylinders around young trees and shrubs. These should extend, where possible, into the top 1-2 inches of the soil. Pre-emergent herbicides used around the base of woody plants prevent voles from finding food and cover there. Mulches, if used around such plants for moisture retention, should consist of gravel or cinders whenever possible. If softer materials, like bark and wood chips, are used, they should be scraped back from the tree during the fall and winter months.
If you insist on reducing the vole population, trapping is the most effective method. For most lawn areas, common wooden mouse snap-traps, baited with peanut butter (or a peanut butter and rolled oats mixture) and placed along the runways at right angles to them can quickly reduce vole populations in a matter of a few days.
Photo credits: Meadow vole, Roger W. Barbour, Smithsonian Natural History Museum; Vole tracks, http://ICWDM.org
"Arrgh! There's a snake in the yard!" This is often the reaction of people who come into contact with these common Midwestern wildlife. Unfortunately, in our hysteria, we often strike out at these creatures--with shovels, hoes, even lawnmowers--with lethal results. Our fears are often the result of a combination of childhood experiences and a great deal of misinformation. Educators find, however, that if we can replace the myths about these animals with facts, the fear is very often replaced with interest. Indeed, truth often is stranger than fiction!.
Snakes are reptiles. As such, they have a backbone, often with over 300 vertebrae. They are "cold-blooded", taking their body temperature from their surroundings and therefore, seeking winter places that remain above freezing. They lay eggs and do not care for their young after birth. Two Midwestern types, garter snakes and rattlesnakes, retain their eggs inside their bodies until they hatch, imitating a type of "live" birth typical of mammals.
The skins of snakes are smooth and dry, feeling much like the leather on your shoes. Most Midwestern snakes see poorly and cannot wink at you: they have no eyelids! Instead their eyes are covered by a clear single scale that is shed and replaced each time they shed their skin. While lizards have external ear openings, snakes have none. Their main sense organ, then, is their tongue. It is constantly flicking out, "tasting" molecules from the air to detect what is around them. Unlike humans, a snake's tongue is not used for swallowing. Rather, snakes have rows of tiny curved teeth and separated jaws to "walk" their prey down their throat.
They move by means of the rhythmic movement, called "peristalsis", of muscles on their bottom side. This movement allows the broad, strong scales on their belly ("scutes") to push against rough surfaces and move forward. Having no legs or feet, they cannot dig holes but can occupy dens made by small mammals like ground squirrels and chipmunks. They are extremely important predators, eating a variety of insects, grubs, worms, amphibians, and especially rodents.
The 28 species of Iowa snakes range from the tiny and uncommon 7-inch western worm snake to the common bullsnake which can be over 5 feet long. Most common are several species of garter snakes, the fox snake and the bullsnake, all of which are harmless. Timber rattlesnakes are venomous and can be common in some very localized forested areas of the state. All other venomous snakes are either exceedingly rare or absent in most of the state.
Follow these tips for keeping your house unattractive for snakes:
- Do not feed birds from April to October. Birds do not need supplemental food during the growing season and feeders draw in rodents and other small critters, which can draw in snakes. Snakes will hibernate from November until March, meaning homeowners don’t have to worry about encountering any in the yard.
- Keep the lawn mown short. By keeping the lawn very short, snakes are at an increased risk of being eaten by a hawk. Snakes do not like to put themselves in such situations and will generally avoid such areas, thus keeping them away from the house.
- Keep landscaping near the house simple. Avoid rock walls and similar features that draw small animals that snakes like to eat into the area. Also avoid “ponds” and similar features that attract frogs, or that hold small fish that garter snakes like to eat. Keep plantings to a minimum, particularly around buildings, as these provide shelter for both snakes and the prey items they eat.
- Keep areas around the house free of wood piles, debris, etc. Snakes can use these to avoid hawks and other predators and to control their body temperature.
- Install rubber seals on the bottom of any garage or shed doors. This will help keep snakes out of those buildings.
- Check the foundations of buildings and structures. Snakes will often use people’s basements or old cisterns as places to hibernate, and snakes have a tendency to be faithful to those sites. Make repairs between May 1 and October 1 so snakes are out and active and not trapped underneath.
The best recourse when you find a snake in a dwelling is to direct it into a container with a broom and then release it on another area on your property away from your house. Then consider the recommendations above to reduce the attractiveness or accessibility of your home to snakes and other unwelcome critters.
Snakes don't do any direct damage to buildings because they don't dig their own holes, instead using holes other animals have made. Although snakes elicit strong negative reactions among many, Iowa’s native snakes play important roles in the state’s ecosystem, often doing more good than harm for a homeowner through their appetite for more problematic rodents and insects. Managing property to reduce potential attractiveness for snakes is the best way to ensure they play this important role where they belong - outside the home.
Photo credit: Garter snake, Mark Wilson, https://commons.wikimedia.org/
Perhaps nothing is as frustrating to a gardener as losing their hard work and crop to unwelcome wildlife. After working hard all spring to get plants and seeds into the ground, fighting the weather, and conquering the weeds, just when the harvest is to begin some other vertebrate critters begin to harvest the plants. Rabbits, ground squirrels, tree squirrels, pocket gophers, or deer arrive to take advantage of the plantings you have provided--assuming you provided food just for them!
The two major defenses gardeners have against such competition are: repellents and exclusion. Repellents are either area repellents or taste repellents. Area repellents repel the animal by smell. As the name implies, the chemical is aromatic and fills the air in the general area of the planting. The smell is offensive to the animal and it avoids the area. Examples of such repellents include hanging bags of human hair or bars of soap or commercial products like moth balls (naphthalene).
Taste repellents are more effective in that they are applied directly to the plant and repel the animal by having a bad taste. The idea is that the animal may sample the plant once, but the bad taste keeps it from trying it again. Examples include such "home remedies" as cayenne pepper and commercial products containing such chemicals as thiram, putrescent egg solids, or other foul-tasting products.
Repellents are not, however, a cure-all. Area repellents are limited in effectiveness, but may be useful if placed around the perimeter of the garden area. Taste repellents cannot be applied to plants you intend to eat since you would also find the taste offensive, and thus are mostly useful in landscaping. Most repellents must be reapplied regularly, especially after rain or periods of extreme heat. Not all products are registered for or effective against all species. And, if an animal is hungry enough, they will often ignore the bad smell or taste. Despite these limitations, many gardeners may find repellents to be the best alternative in their particular circumstance.
Another more permanent protection against unwanted sampling of your garden is exclusion. You may exclude in several ways, depending upon the area you are in and the situation. Individual plants may be surrounded by plastic tubes, chicken wire, or hardware cloth fences. You may also fence off your whole garden area to exclude the worst offenders – rabbits and deer.
The size and mesh of the fence depend upon what you are trying to exclude. For rabbits, 1-inch mesh "chicken-wire" fence at least 2 feet high will successfully exclude them, especially if the bottom 2-3 inches are buried below ground level. For deer, you may use a variety of fences including electrical tape or strong large mesh of any kind. Old "hog wire" fencing filling many farm gullies will suffice, especially if several sections are erected, reaching a height of 8 feet. In small garden plots, you may be successful with fences somewhat shorter than that, but no lower than 5-6 feet.
Gardeners may find also that general clean-up of garden areas to eliminate the brush, log, or junk piles that provide protective cover for many of the offending critters will help. Also, the presence of pet dogs will often serve as an aversion to these wildlife.
Above all, keep in mind that a reality of gardening is dealing with pests and factors out of your control like weather. Gardens inevitably attract both those critters you want and those you don't. Some damage should be expected. When your tolerance level for such damage cannot be raised any higher try some of these repellent or exclusion methods.
Pee-Yew! It's fall and you've caught a whiff of that unmistakable pungent smell drifting on the night air that could only belong to the skunk. Skunks, now classified in the family Mephitidae, like members of its former family Mustelidae, the weasels (mink, weasel, badger, otter, etc.), emit an oily musk from their anal glands. Members of these families use musk to mark territories and den sites, and attract a mate. But, in the case of skunks, they can release a potent mist or stream, at close range and up to 20 feet, to defend themselves against predators!
Iowa has two species of skunks: the striped skunk and the spotted skunk. The latter, also known as a "civet cat", is smaller than the striped skunk, has white spots and shorter, broken white stripes against black fur, and is listed on Iowa’s endangered species list. Little is known about where they may still be found in Iowa. With the loss of small farms, diversified agriculture, and the lack of rodent prey attracted to readily available grain, once stored in open cribs, the “civet cat” has all but disappeared from Iowa’s farms and countryside. Meanwhile, the striped skunk has remained ubiquitous, occasionally to the chagrin of a dog or homeowner.
Striped skunks are typically nocturnal, but during times of increased feeding, such as spring when the female is pregnant and fall, when fattening up, they can be seen earlier in the day or evening. Seeing a skunk in daylight is not necessarily an indication of rabies and should not cause undue alarm. Pay attention to the overall health and behavior of the skunk, and if it appears to be going about its business, do not disturb it and maintain a respectable distance.
Striped skunks typically have litters of 4 to 6 young born between May and June. The young stay with the female until fall, when they begin to disperse in search of their own territories and winter den sites. This behavior, known as the “fall shuffle” puts roaming skunks at risk, increasing encounters with humans, our pets, and predators. As evidence of this shuffle, notice how many road-killed skunks and raccoons you see during the fall.
Striped skunks have a very good sense of smell, and being omnivores, consume a varied diet, preferring insects and their larvae. They also consume eggs, berries and other fruits, and in winter and early spring when other food is scarce, small rodents. In late summer and fall, skunks can cause damage to lawns as they search for insect larvae, such as white grubs. The damage is distinguishable from that caused by raccoons, as the sod appears as if someone has neatly rolled it back with the intent of transplanting it elsewhere. Any control of this damage must first begin with the control of white grubs in the soil. Contact your local County Extension office or Horticulture Extension for the appropriate timing and chemicals necessary to control grubs. This feeding activity in the fall builds up fat reserves for winter. Skunks do not hibernate but will sleep for a week or two during severe winter weather.
During the fall, skunks, as well as woodchucks, raccoons, rabbits, chipmunks, opossums, and others are all on the lookout for winter shelter. The deck or patio becomes a popular hangout for these critters, sometimes for the long run. Skunks can cause an odor problem, not to mention the damage and mess of digging. The solution is to exclude them, thus preventing access in the first place. This can be done by adding a fence below the deck, using 1/2 inch mesh hardware cloth, attaching it firmly to the deck frame and burying it 10-12 inches below ground.
Fall is also a common time when your dog or cat, if left to wander at night, may bring home the odiferous perfume of a “not-so-romantic” encounter with a skunk. What to do? The commonly suggested bath in tomato juice fails to adequately do the job and usually just make us or pets smell like tomatoes and skunk! If you, your pet, or side of your house is ever sprayed by a skunk, there is a very effective home remedy that works on almost all surfaces. The ingredients are inexpensive and commonly found around the house.
In an open container, mix together ¼ cup baking soda, a fresh 1 quart bottle of 3 percent hydrogen peroxide, and 1-2 teaspoons of liquid dish detergent. This solution must be used right away and cannot be stored. For pets and people, thoroughly work the mixture into the fur, hair, or skin, avoiding the eyes and mouth, and leave on for 5 minutes. Then rinse with fresh water and repeat if necessary.
This should eliminate the order, but avoid getting it on cloths that you don’t want bleached. Well laundered and deodorized clothing will, over time and exposure to air, lose the odor, although the garbage may be their ultimate fate way before then!
Skunks may get a bad rap for the smell, but remember to appreciate their striking pattern of black and white and their ecological role as consumers of our insect pests. And keep the hydrogen peroxide handy, just in case!
Photo Credits: Skunk damage, Iowa State University Extension and Outreach; Deck fencing exclusion, Jim Pease Iowa State University
Bats are extremely valuable in insect control. We want them flying around outside gobbling mosquitoes, crop-damaging insects, and others. We just don't want to share their living space with them!
There are no registered 'baticides' available for use against bats. Even if there were, one would still have to locate and close up entrance holes to prevent other bats from recolonizing the same area in a building. Like almost all other animal species, Iowa law protects bats. While homeowners are allowed to protect their property, repellents are largely ineffective, including those expensive "sonic" or "ultrasonic" devices and the relatively inexpensive mothballs. Thus, excluding bats from buildings is the only way to deal with them. Understanding some bat habits is the key to successful exclusion.
What you need to know about the bats sharing your home
First, bats are nocturnal. They emerge from their roosts at dusk each evening, searching for food and water. Thus, exclusion activities must be done after they've emerged, NOT during the daytime. Blocking entrances during the day only guarantees more severe problems, increasing the likelihood that they will come down through the walls in search of a way out or die in the house, causing a different set of problems for the homeowner.
Second, bats follow air currents. Any spaces--say, your attic and a bedroom--that have different temperatures and are connected by a crack or hole, automatically have airflow between them. Bats simply follow those air currents. Blocking those air currents is the key to successful bat exclusion.
Third, August and September are the best time to do the exclusion. Bats are mammals and often form maternal colonies, a mother and her one or two young hanging together with dozens of other mothers and young. Since young bats are naked and blind, mothers leave them behind each night to seek food and water, returning later in the night to nurse. If exclusion is done prior to August you may only exclude the mothers and end up having the young die in your house.
Finally, only two of Iowa's nine bat species, the big brown bat and little brown bat, commonly use buildings in the summer for colonies. Only the big brown bat uses buildings in winter. It is mainly these two species that cause problems for homeowners.
Step 1: Find the entry points.
Finding the entrance can be a family affair. Take lawn chairs, your favorite drinks, and a flashlight and sit outside in your yard about sundown. Watch for emerging bats. Check the obvious places first: around the chimney, gable vents, or roof vents. Don't forget the not-so-obvious places also: under the eaves, behind the rain guttering, under torn shingles. All these are common entrance sites and indicate that some repair is in order. Some buildings have more than one entrance site. Any holes the size of your thumb or larger are enough for bats to find and exploit. Don't forget, many bats may use the outside of your house without posing any issues to the inside, so be sure to find likely entry points, as illustrated in this figure.
Step 2: Allow the bats out, but not back in.
Once you've identified the entry points around your home build a one way door on the outside of the house to allow the bats to crawl out of the hole, but not fly back in. A one-way door will be anchored above the hole and then hang loosely below. It can be made from half-inch mesh bird netting, screen wire, heavy cloth, or even a sock with the end cut off to create a tube aroudn the hole.
Let's say, for example, the entrance is a crack one half inch wide and 6 inches long. Cut a piece of netting or screen. Place it over the entrance crack so that the entrance is in the upper half of the net/screen. Use duct tape to tape the top and two sides of the screen to the building, leaving the bottom edge open and just loose enough for the bats to squeeze out. Bats will emerge that evening, hit the screen, crawl around until they find the bottom loose, and then fly out. When they return, they return to where the air current is--the crack--not to the bottom of the screen. If you leave this up for 4-7 days, you can be assured that all bats are out and the repairs can be made, this time during the daylight hours.
Step 3: Repair the holes and entry points
Use foam sealants, fine (half inch or less) wire mesh, new boards or soffit, plaster, or any other means necessary to fill all holes in and around your home to prevent bats from finding their way in again.
For more detailed information on issues with bats around the home visit the detailed article on bats from the Prevention and Control of Wildlife Damage manual.
Photo credits: One-way door, Bat Conservation International, http://www.batcon.org/