Got Nature? Blog

Remove perches from wildlife nest boxes like the bluebird box pictured here. Perches allow undesirable birds to harass native cavity nesters and take over a nest box.

Even though we have had some rough weather lately, this winter didn’t seem so bad to me. Now that the weather forecast is looking positive and the days are getting longer (this month, we gain about 75 minutes – I am embarrassed to admit that I check this frequently during the winter because it helps me get through the winter doldrums), it is a good time to think about wildlife habitat projects.

Sometimes landowners and homeowners can be overwhelmed by all the different ways they can help wildlife on their property. An easy project that is also fun to build and place on your property is a nest box. You don’t want to wait much longer. Erect your nest box well before the average start of the nesting season (most birds start in mid-April, but some start sooner). Some species will set up their nesting territory three to four weeks prior to egg laying.

Many species of native birds and mammals will utilize nest boxes. When we put out a nest box, all we are doing is replicating what nature already provides with cavities in both live and dead trees. Woodpeckers are primary cavity users because they create their own. Other birds and mammals are secondary cavity users because they use what is already there – either those that occur in older, dying trees or those that are created by woodpeckers. Installing nest boxes in areas where cavities are likely scarce such as urban environments or young woods may be particularly beneficial.

Tips

• ​Use quality materials that are weather resistant. Exterior grade plywood and lumber are good choices. Cedar and other rot-resistant woods are best. Avoid using treated lumber and metal.
• Avoid painting or staining inside nest boxes. Painting the outside can prolong its life and may be attractive for some species (white for purple martins, for example).
• The roof should be sloped to allow water runoff and should hang over the sides.
• Drill at least four 3/8-inch drainage holes on the floor.
• The roof or one side should open to allow easy access for cleaning.
• Avoid perches. Natural cavities don’t have them and neither should your nest box. Perches also allow European starlings and English house sparrows, non-native invasive species, to harass native cavity nesters and take over a nest box.
• Near the top of each side, leave gaps or drill 5/8-inch holes (at least two per side).

More tips on design, such as nest box specifics by species (dimensions, hole size and placement, box placement and location), maintenance and problem species, can be found in our Nest Boxes for Wildlife publication​.​

Other resources available:
Attracting Hummingbirds to Your Yard, The Education Store
Birds of Benton County, Indiana, The Education Store

Brian MacGowan​, Extension Wildlife Specialist
Department of Forestry and Natural Resources, Purdue University

“When it snows…
and temperatures drop,
That’s when you’ll hear
The Snap, Crackle and Pop.”

Few things can compare to the peacefulness of walking in a forest filled with snow covered trees until you hear a snap, crackle or an explosive “POP” echoing through the woods. What on earth was that? If the noise is followed by a “whoosh,” it may be a limb that just broke and crashed to the ground. If it sounded like a gunshot but nobody is there, you may be listening to the sound of a frost crack forming on a tree.

What are frost cracks?
Nobody knows for sure. You may hear one happen, typically on a cold late winter morning after a warm spell. They sound like muffled to loud rifle shots. Typically, these cracks occur on the south side of the trunk between two and five feet up the tree (when measuring from the ground). With leaves on, water is pulled upwards from tree roots through the xylem vessels by the differences in water potential from the air to the soil and escapes through the leaves (the soil-plant-air continuum).

Water in the plant is under a negative water potential, or in common terms, under tension. In the winter, when deciduous trees have no leaves, the water pressure in the sap becomes positive. A flow occurs where water moves up in the xylem and cycles down in the phloem (food conducting cells). The mechanism of this winter flow in temperate trees is not well understood physiologically. The sap increases in simple soluble sugars as the cold weather begins and increases until midwinter to work like antifreeze, depressing the freezing point of water. This is why maple syrup can be tapped in late winter.

Scientists are challenged to study the phenomena of frost cracks. They involve thousands of xylem vessels in a very narrow vertical line bursting all at once – as if a line of sap is too low in sugar concentration – and then freezes hard explosively bursting the vessels. After several growing seasons, most trees will heal over the crack, but callus growth makes them appear wider. Valuable timber logs can still be profitably harvested with frost cracks as millers can cut through them to minimize the defect.

Species with darker colored bark and thinner bark can be affected by frost cracks. Some genotype effects have been found in black walnuts at Purdue. Field conditions and topography that effect cold air movement can affect frost cracks. Most form on the southwestern section of the trunk, the area most affected by warming from sunlight during winter afternoons. Somehow, this conditioning sets up the tree when temperatures plummet to single digits (in Fahrenheit) or lower, especially after a warmer period.

So if you wander through the woods this winter, stop but don’t “drop” when you listen to the sounds of the trees.

“When the snow twinkles
and the skies are bare…
Temperatures drop
and a chill fills the air.
If you listen real close
and adjust your cap,
You just might hear
a tree go ‘Snap!’”

Resources
Bark Splitting on Trees, Cornell University
Video: How Do Trees Survive Winter? MinuteEarth
Winterize Your Trees​, The Education Store

Shaneka Lawson, Adjunct Assistant Professor
Department of Forestry and Natural Resources

James McKenna, Operational Tree Breeder
Department of Forestry and Natural Resources​​​​​