The nestboxes at Haehnle Sanctuary consist of 25 boxes sized for small cavity nesters, 2 American Kestrel boxes, and 5 Wood Duck boxes. We also monitor a Purple Martin rack. The boxes are monitored starting in late March to typically the end of July, sometimes into August depending on weather. The two most common species attracted to the nestboxes at Haehnle are Tree Swallows and Eastern Bluebirds.

Tree Swallows arrive in Michigan in late March to April and immediately begin trying to establish their nesting territory. During the nesting season it's very typical to see them guarding "their" boxes. Tree Swallows can be very protective of their territories, so it's not uncommon to get dive bombed by them while they are nesting.

Tree Swallows typically only have one brood per season, so there is some urgency to establish those territories so they can raise their young in time to migrate south in the fall. Tree Swallows will generally lay somewhere between 4-7 white eggs per brood. They build a nest made of grasses, then line it with feathers, as shown in the photo above. Incubation begins after the last egg is laid, and will take approximately two weeks before the eggs hatch. Both adults will feed the nestlings (primarily insects) for the next two to three weeks until the nestlings are ready to fledge. When the nestlings fledge, they will hopefully be strong enough to make their first migration flight south.

In August, Tree Swallows will migrate to the southern part of the U.S., Cuba, Mexico, and Central America. They remain there for the winter where more food is available, then migrate back to the U.S and into Canada again the following year to breed.

Eastern Bluebirds are year-round in Michigan. Most people think they migrate, and some bluebirds will move further south to areas where more food is available, but they move to more forested areas in the winter here in Michigan, which is why most people won't see them during those months. Their diet changes from eating insects, which are easy to find in open grassland areas, to fruit and berries which are in brushy, forested areas.

Bluebirds will have 2-3 broods per year. The male bluebird will put a few pieces of grass in a nestbox to see if the box is acceptable to the female, at which time she will complete the nest is she approves. The female will lay 4-6 blue eggs. Incubation lasts two weeks, at which time both adults will feed the young (primarily insects). The nestlings will fledge at 14-16 days old. They will stay in the area and continue to be fed by both adults. Some fledglings will assist in caring for the next brood.