Habitat structures

A feature that enhances habitat for a variety of species.

Practice description

Habitat structures are anthropogenically created or intentionally retained features within habitats that provide opportunities for germination, foraging, cover, nesting, roosting, hibernation, basking, or other activities. 

• Soil exposure
• Snake hibernacula
• Brush piles
• Coarse and fine woody material
• Snags and cavity trees
• Bird nesting structures
• Bat roosting or maternity trees
• Bat roosting structure
• Canopy gaps
• Legacy trees 

Goals and ecological processes 

Habitat structures are intended to supplement naturally occurring habitat features that are typically created through ecological processes such as flooding, ice or wind events, wildfire, pathogens, and naturally occurring changes in vegetation over time, succession. These events result in exposed soil, downed logs, treetops, or whole trees, snags, cavities, canopy gaps, or old growth features of mature forests such as legacy trees. 

Target habitats and species 

Habitat structures or features enhance habitat for plants, bees, other insects, amphibians, reptiles, birds, bats and mammals. A variety of habitat structures may be included in management of the following habitats.

• Mature forest
• Young forest
• Cultural shrubland
• Cultural grassland
• Dry grassland
• Shrub swamp
• Wet meadow
• Small streams 

Associated practices 

Selective tree removal

Prescribed fire

Grassland bird management

Mowing and mulching

Prescribed fire

Soil exposure 

Exposed soil is an important habitat feature offering germination sites for plants, nesting opportunities for some insects and turtles, or basking habitat for reptiles. Providing access to bare soil is particularly beneficial in barrens, sandplain grassland, and cultural shrubland habitats. Soil exposure can be achieved through the use of prescribed fire, or through mechanical processes such as scraping, disking, plowing or harrowing. The following guidelines provide details about the appropriate placement or timing and other considerations to make for conducting activities that expose bare soil. 

• Plant germination sites: Exposure to bare soil provides germination sites for native warm season grasses and flowering plants. Where invasive plant species or aggressive native species such as clonal goldenrod are dominant, a fall herbicide application followed by dormant season light discing or harrowing can break thatch and increase germination sites for native plant species.
• Native bees: Ideal nesting opportunities for many native bee species occur near nectar sources on south-facing, well drained slopes where plants are sparse and direct access to soil is available. Dry, sandy areas that are covered by duff and dense vegetation but would could otherwise support nesting bees, can be scraped just deep enough to expose the mineral soil. These scraped areas should usually be relatively small (~2,500’ square), but if a habitat is large enough, multiple scrapes can be made. If the openness of a scrape cannot be maintained over time with periodic disturbance (ex. prescribed fire), creating new adjacent scrapes will ensure that adequate nesting habitat is available through time.
• Turtle nesting sites: Turtle nesting habitat consists of open areas with bare, often sandy, well drained substrate. Female turtles will travel great distances from feeding wetlands to lay eggs if an adequate nesting opportunity is not nearby, and so one important approach to reduce road-related mortalities is to provide access to nesting habitat near feeding and overwintering wetlands. MassWildlife has developed guidelines for creating nesting habitat for turtles where nesting habitat is lacking. 

Snake hibernacula

Access to suitable hibernaculum is a critical component to the life history of all New England snakes. Lack of access to hibernaculum is also a major limiting factor to the number of snakes a site can support. Natural features in which snakes will hibernate include deep bedrock rock crevices, talus and traprock ridges. In areas where these features are limited, or where threats such as road crossings are present, hibernacula can be created. Many snakes and multiple species of snakes will share the same hibernaculum if it is large enough, and therefore the creation of a large hibernaculum can greatly bolster the carrying capacity of snakes on a landscape.

• Select a location well away from roads associated with a south facing slope consisting of sandy or sandy loam soils so that it will not become flooded. It should have an open canopy to provide basking areas for snakes in the early spring and late fall.
• Dig a hole that is a minimum of 15’ in diameter. It should extend well below the frostline, but remain just above the water table so that it is humid, but does not freeze of flood.
• Fill the hole with round rocks ranging from 6-18” in diameter. The voids between the rocks should be large enough so that snakes can pass through them, but not so large that cold air easily penetrates to the bottom of the hole. Concrete pipes can be placed at various depths to provide hibernation chambers. Avoid using materials that will break down and fill chambers and passageways such as tree limbs, logs, or other woody debris.
• Consider the potential for intentional human-caused snake mortality when siting hibernacula. Hibernacula on land open to the public should be easily monitored by managers, and if possible, surrounded by chain link fence to reduce the likelihood of someone entering the hibernacula to purposely harm snakes.

Brush piles

Brush piles offer a dense cover of branches and twigs that can provide forage, sites for denning, perching, or nesting. The gradual breakdown of fine and coarse woody material contributes to ecological functions on the forest floor. This habitat feature can be created by piling brush or hinge cutting trees in mature forest, young forest, or old field habitats.   

• Construct one or two brush piles per acre to provide cover, perch sites, and nesting sites. Begin with a bottom layer of logs spaced 10"-12" apart and a second layer perpendicular to the first and also 10"-12" apart then top the pile with smaller limbs and branches. Limbs and branches can periodically be added to extend the longevity of the piles.  Brush piles should not be constructed in areas that are intended to be treated with prescribed fire.
• Hinge cutting is another alternative for providing piles of brush cover on the forest floor. This practice involves cutting a tree part way to fell only the top. The top remains alive providing forage and cover. 

Coarse and fine woody material

Coarse and fine woody material consists of fallen trees, downed logs, large fallen limbs, treetops, or slash. This habitat feature may be present in terrestrial, palustrine, or aquatic habitats. Ecological processes including flooding, wind events, icing, or wildfire typically contribute woody material to these habitats. Coarse and fine woody material may be intentionally placed or retained to enhance germination, foraging for insects, cover for amphibians, reptiles, and fish, spawning sites, or to provide display habitat for ruffed grouse. Coarse and fine woody material can provide other benefits and contributes to ecological processes of the habitats within which they are present. 

• Terrestrial habitats including mature forest, young forest, and cultural shrublands can be enhanced by the addition of coarse and fine woody material. Downed woody material/slash currently present as a result of other management activities such as tree clearing, or thinning may adequately offer this habitat feature. Cutting two trees per acre that are 14 to 16 inches in diameter and leaving logs that are at 8 to 10 inches long on the forest floor will provide coarse woody material. Retaining tree tops will offer fine woody material. Girdling trees is also a technique that can be used to contribute coarse and fine woody material to the forest floor over time. Coarse woody material should not be placed or intentionally retained as described above in habitats where prescribed fire will be implemented as a management practice.
• Palustrine habitats, particularly forested swamps, often contain coarse and fine woody material as a result of flooding that kills trees. Standing dead or dying trees in wetland habitats provide nest sites for herons, cavities for nesting songbirds or wood ducks, and foraging opportunities for insects and birds. Downed limbs and trees offer basking sites for turtles and refugia for fish. Girdling trees in wetland habitats is a technique that can be used to create this habitat feature.
• Aquatic habitats with coarse and fine woody material provide increased habitat complexity consisting of cascades riffles, and pools. These provide escape cover, basking sites, gravel bars for spawning, and foraging habitat for insects. In addition, woody material in streams contributes to the ecological process of connecting the aquatic habitat to the adjacent upland habitat and the floodplain slowing the flow of water and enabling water to move over land, which contributes sediment and nutrients to the riparian habitat. Techniques for providing coarse and fine woody material in aquatic habitats are described in the channel and shoreline habitat practice.

Snags and cavity trees 

Snags are standing dead trees. Cavity trees are live or dying trees with broken limbs and branches. Each are naturally created in flood prone areas, by insect outbreaks, fungal or other tree diseases, and as the result of wildfire. Snags and cavity trees can also be created naturally by foraging rodents, rabbits, birds, or insects. Snags and cavity trees increase foraging, perching, and nesting opportunities for birds, small mammals, and bees in upland forest, forested swamp, shrubland, or grassland habitats. As limbs and snags decay and fall they also serve as coarse woody material that offers cover and foraging habitat for ground dwelling animals and germination sites for some plants.

If there are insufficient existing snags on a landscape, snags can be created by girdling. Some considerations regarding snags include:

• Species that use snags are typically more concentrated near water.
• Retain snags, as well as stumps for cavity nesting bees at the edges of grasslands and shrublands.
• Nest boxes can be installed to provide cavity nesting opportunities for songbirds, especially in grassland and shrubland habitats.
• Caution should be taken to locate snags away from areas such as trails where they could be a safety concern if they fall. Retaining a cluster of live trees around snags can reduce safety risks.
• The use of prescribed fire can result in creation of snags and cavity trees. Additional snags should not be created in habitats being managed with fire. Snags present a hazard for prescribed fire crews and add great complexity to prescribed fire events.  

Bird nesting structures

When tree cavities are insufficient or unavailable, nesting structures provide birds with opportunities to breed. Many common bird species such as house wren, carolina wren, black-capped chickadee, eastern bluebird, and tree swallow use nest structures installed within grassland or shrubland habitats. Barred owl and screech owl will use nest boxes installed in mature forest habitats, and wood duck will use nest boxes in a variety of wetland habitats. The Massachusetts Audubon Society provides detailed information about birdhouses including a birdhouse and nesting chart specifying size and placement appropriate for different species that can be referenced for additional species. 

Rare or declining species that use nest structures include American kestrel and barn owl. Tern and osprey nesting opportunities can also be enhanced with nesting structures. Following are guidelines for constructing and installing American kestrel, wood duck, and osprey nest structures in those habitats where they are likely to be utilized by these species. Consult MassWildlife Habitat Program staff for further guidance when planning the use of bird nesting structures for rare or declining species.

American kestrel nest structures

Open fields, pastures, hedgerows, and power line rights-of-way comprised of or surrounded by at least five acres of grassland or shrubland habitat and within 20 yards of trees with dead limbs, utility poles, or other perches make the best habitat in which to place American kestrel nest boxes.

• Purchase or construct an unpainted, unstained, or otherwise untreated nest box made from white pine or cedar that is rough on one side. See attached instructions for nest box building or characteristics a nest box should possess.
• Place nest boxes 12 to 20 feet high on a pole in a field at least 50 yards from woodland edges and away from agricultural fields treated with pesticides as the primary food source for American kestrel is insects. If more than one box is installed, they should be at least 1,000 feet from each other.
• Face the box entrance east/southeast to avoid direct winds and to take advantage of the sun's rays.
• Install a predator guard on the pole 6 to 12 inches below the bottom of the box and remove vines or other climbing vegetation from the pole.
• Line the bottom of the box with 2 to 3 inches of wood chips or shavings, straw, or pine straw.
• After the nestlings have fledged, generally by August 1, clean all nesting materials out of the box.
• Boxes should remain out during the winter to provide cover for kestrels, screech owls, and other resident birds.

Wood duck nesting structures

Cavities in snags or live trees provide habitat features preferred by wood duck for nesting. They nest in habitats consisting of ponds with marshy cover or marshy borders, marshes or wet meadows that contain potholes and other open water areas throughout the summer, slow streams with quiet pools and backwaters that have aquatic cover available, and forested swamps or beaver flowages that hold standing water at least until August. Nesting opportunities for wood duck can be offered by installing nest boxes. 

• Placing boxes over water is the preferred location with the greatest chance of nesting success. It is best if only a few boxes are erected in any new area at first. Box numbers can be increased when wood ducks are utilizing at least half of them. Erect the box on a wooden pole, iron pipe, or other suitable structure out in the open water of a marsh, pond, stream, or swamp. This type of over-water erection has a higher rate of use by wood ducks, predation is reduced and competition from squirrels is eliminated. Also, ducklings are spared the hazardous overland journey to water. Sometimes isolated dead trees are found standing in the water some distance from dry land. If such a tree is used for placing a box, the top and limbs should be trimmed to prevent toppling in heavy winds.
• When the pond or marsh bottom will not permit a pole to be firmly driven into the mud, the only alternative may be to erect nesting boxes on trees along the shoreline. These boxes must be protected with predator guards, and many may be taken over by gray squirrels. Limbs should be removed allowing wood ducks a clear flight path to the entrance of the box.
• All nests should be checked and cleaned out annually to make the boxes available for duck usage. Do not do this during the wood duck nesting period, April to July. Repair and clean out as necessary. Boxes filled with debris from squirrels or starling nests will not be utilized by wood ducks. Replace nesting litter or saw dust or shavings as necessary and check that the box cover is securely fastened.

Osprey nest structure

Osprey prefer to nest in areas with sparse tree cover near shallow waterbodies (fresh or salt), and nesting platforms are more likely to be used if there is currently another active nest within a few miles. A nest platform can be provided according to the following guidelines and attached nest platform construction designs from The Cornell lab of Ornithology Nest Watch Platform for Success, Center for Conservation Biology Osprey Watch, The International Osprey Foundation, and New Jersey Division of Fish and Wildlife webpages. 

• Locate the platform within 1,600 feet of water. If the platform is to be located in water, it should be at least 15 feet above the surface.
• Ensure that the platform or snag is at least 20 feet tall and/or taller than any nearby trees.
• Follow a platform construction design that provides instructions for one that is at least 3 feet by 3 feet and can support 300 pounds.
• Provide multiple drain holes in the base of the platform to prevent flooding during heavy rain.
• Offer at least one perch pole on the platform and a perch pole on the ground within 50 feet of the nest.
• Include a guard to protect eggs and young from predators that will climb the pole, such as raccoons.

Bat roosting and maternity sites

Most colonial bats are found near habitats near where they forage for insects, such as rivers, lakes, bogs or marshes. The closer roosting or maternity sites are to foraging habitat, the greater the probability that bats will benefit. Both live and dead trees are habitat features on which bats depend for roosting and foraging. Bat boxes can be also offered to provide both roosting and foraging opportunities. Roosting or maternity sites located more than one-half mile from foraging habitats have a greatly reduced probability of being used. Bat houses or boxes can be useful in providing secure roosting sites for bats and may be especially helpful in providing habitat for bats that are displaced from dwellings. 

Retain trees preferred by bats including ash, cherries, elms, maples, spruce, walnut, or willow with the following features 

• thickly leafed parts
• hollow trees
• trees with loose bark
• clustered stands of large trees, especially live or dead hardwoods with large, tall cavities
• dead leaves on mature live or recently dead deciduous trees
• dead needles of living pine
• promoting predominately hemlock, spruce, and white cedar in the foothills of 2,000 foot mountains with caves 

Install bat boxes using a design available from the Massachusetts Division of Fisheries & Wildlife under the following conditions 

• on the side of a building, on a tree, or on a pole roughly 12-15 feet above ground
• preferably where it will receive morning sun but will be shaded during the afternoon
• in a location relatively protected from wind

Canopy gaps

As a habitat feature, canopy gaps are openings in a mature forest canopy that are less than five acres. They are naturally created as a result of storms or pathogens that remove individual or small groups of mature trees from the canopy. The resulting gap allows sunlight to reach the forest floor and stimulate the germination of herbaceous and woody vegetation. The small patch of vegetation on the forest floor offers food, cover, perching, or nest sites for ground dwelling forest animals. Some mature forest breeding birds that build nests on or near the ground depend patches of dense vegetation on the forest floor. Other animals such as moose or New England cottontail are provided with foraging opportunities, especially important in winter months. Canopy gaps can be created in mature forest or forested swamp habitats. 

Legacy trees

Legacy trees are trees that offer a variety of habitat features which typically develop as they age. These can include large crowns, thickly leafed parts, broken limbs, cavities, or loose bark. In addition, they contribute coarse and fine woody material to the forest floor as limbs or crowns break. A minimum 5-10% of well-distributed overstory trees consisting of a variety of species in a mature forest habitat can be designated as legacy trees retained in perpetuity. Retention of legacy trees within 1,000 feet of vernal pools in upland forest habitats is recommended and should consist of deciduous species.