For the Love of Nesting Birds

Observations from the Field

Betsy Cross

Some of us are fascinated by the mysterious methodologies of birds’ building nests and fledging their young. I’ve been peering into bird nests for as long as I can remember. But when I discovered that I could put a wooden box on a pole and periodically open a hinged door to see a bird’s eggs and chicks inside and then watch the parents deliver food and eventually coax fledglings out for their first flight, I was hooked.

Every year in the late fall, bird enthusiasts and citizen scientists across the country start preparing for the spring nesting season, which in Central Texas begins in early February. We never tire of monitoring bird boxes, nest cams, and natural cavities to get an intimate glimpse into the secret lives of birds. We log data to help experts track reproduction numbers, to understand migration patterns, the impact of habitat loss and the effects of climate change, and ultimately to diagnose the viability of a species.

Each bird species has a unique nesting style. Nest placement and construction preferences are specific to the species. In some species, both parents work together to construct the nest and take turns incubating the eggs and bringing food to hatchlings. For others, it’s a single parent event, start to finish. Some birds parasitize the nests of others, laying eggs in the nests of a different species and leaving the rearing of young up to the foster parents.

The closer I observe the nesting patterns and preferences of different birds, the more I consider questions such as these:

Why do some birds build open-air nests in the crook of a tree branch while others are cavity nesters?
Why does an Ash-throated Flycatcher build a nest foundation of Ashe juniper strips and then cover it in heavy pelt-like layers of animal fur?
Why do titmice add a piece of snakeskin to their nests of fresh green moss lined with soft fur (and sometimes with pink insulation or other artificial stuffing)?
What would drive an Eastern Phoebe to choose a half-inch ledge under my front porch, onto which it applies mud in the form of a cup and then covers it with soft trailing moss and lines the cup with a single variety of grass in a perfect oval?

These unique qualities are the signatures of birds.

Project 702 RM Bluebird Nest Box Monitoring

I’ve monitored bird boxes for over ten years, the last five years at Jacob’s Well in Hays County, Texas, under HCMN Project 702 coordinated by Hays County Master Naturalist Bonnie Tull. I’ve documented 6 species of birds that utilize the 11 nest boxes across the 81-acre property at Jacob’s Well. The Eastern Bluebird is our target species for habitat enhancement. Their populations fell in the early twentieth century when aggressive species such as European Starlings and House Sparrows were introduced. These non-native species made natural nest holes increasingly difficult for bluebirds to hold on to. In the 1960s and 1970s the establishment of bluebird trails and other nest box campaigns alleviated much of this competition, especially as people began using nest boxes designed to keep the larger European Starling out. Eastern Bluebirds have been recovering since. https://www.allaboutbirds.org/guide/Eastern_Bluebird/lifehistory.

The Brown-headed Cowbird, a native to North America, can also pose a threat to bluebirds. Female cowbirds lay their eggs in the nests of other birds, usually at the expense of at least some of the host’s own chicks. Female cowbirds forgo building their own nests and instead put all their energy into producing eggs, sometimes more than three dozen a summer. Cowbird eggs hatch faster than other species’ eggs, giving the cowbird nestlings a head start in getting food from their unwitting adoptive parents. Young cowbirds also develop at a faster pace than their nest mates, and they sometimes toss out eggs and young nestlings or smother them in the bottom of the nest. https://www.allaboutbirds.org/guide/Brown-headed_Cowbird/overview

Through Project 702, Hays County Master Naturalists are contributing to the creation of additional habitat for bluebirds. So you might ask, what about the other five species that are using the boxes? I do not discourage nest box occupation by the other species discussed below, though proper placement of nest boxes for use by bluebirds is an important consideration and a priority. Furthermore, it’s illegal to disturb any native species’ nests.

In addition to the bluebirds and other bird species in the boxes at Jacob’s Well Natural Area, I’ve documented a variety of bird species nesting in natural cavities on that property. The following images are all part of my contribution to Project 702 at Jacob’s Well. Let’s take a look. Click on any image to scroll through a full screen view of the photos in a series.

Eastern Bluebird
Sialia sialis

Black-crested Titmouse
Baeolophus atricristatus

Bewick's Wren
Thryomanes bewickii

Ash-throated Flycatcher
Myiarchus cinerascens

Carolina Chickadee
Poecile carolinensis

Carolina Wren
Thryothorus ludovicianus

Life in A Dead Tree

It’s interesting and educational to monitor and document birds in nest boxes, but I never miss a chance to look for other nesting behaviors along the way. Cavity nesting birds, such as the ones shown above, also utilize old woodpecker holes, and they can provide fascinating birdwatching opportunities.

In the early Spring of 2018, I noticed a lot of bird activity—bluebirds, chickadees, woodpeckers—around a dead tree on the west side of the path at Jacob’s Well between the upper parking lot and “The Well.” I looked closely and discovered that these cavity nesters were exploring a woodpecker hole. Eventually, the Ladder-backed Woodpeckers won the battle for occupancy. After all, it was a woodpecker hole, and maybe they were the original creators.

March 9 - First photo of the male Ladder-backed Woodpecker cleaning out the nest. I photographed him each week throughout the nesting cycle. Sometimes he would be peering out when I arrived. Other times if I waited a bit, he would fly in.

Then in the Spring of 2019, a new tenant moved into the dead tree—the same tree used by the woodpeckers the previous year. If you look closely at this first photo below (or click to enlarge it), you will see the woodpecker hole just about level with the top of the oak tree in the background.

A closer look at the tree reveals an Ash-throated Flycatcher on the high left perch. That spot, and especially the limb on the right side in closest proximity to the hole, served as “staging perches” for the parents tending the nest.

In the Spring of 2020, an Eastern Bluebird couple found its way into the dead tree and raised a family. On one occasion, I observed the male bluebird defending his turf at the woodpecker hole. The aggressor appeared to be the Ash-throated Flycatcher.

May 10 - The male bluebird brings the female in to evaluate the woodpecker hole as a potential nesting site. They study the landscape from the staging perch as she considers the situation.

I’ve had the opportunity to document different bird species that utilize old woodpecker holes in a variety of dead trees at Jacob’s Well Natural Area—bluebirds, woodpeckers, chickadees, flycatchers. The amount of activity and the diversity of birds that nest in woodpecker holes is impressive. I would submit that as long as a dead tree doesn’t create a safety concern, it should always be left in place for the benefit of these birds.

We know the bluebird population in Texas was negatively impacted by Winter Storm Uri in mid-February, 2021…

…and it’s important to note that since June, 2020, when the bluebirds last nested in the woodpecker hole, I have not seen an Eastern Bluebird at Jacob’s Well—not in a nest box and not in a tree.

Rebekah Rylander PhD, who was still conducting her Black-crested Titmice research at Texas State University at the time, reported that a manager at Freeman Ranch opened one of her nest boxes after the storm and found 12 dead bluebirds inside.

Texas Bluebird Society President Pauline Tom reported in July, 2021, that Cornell’s eBird app recorded only 7,064 Eastern Bluebird sightings in Texas in March, 2021, compared to over 10,000 in March, 2019, and in March, 2020. She also mentioned that at a festival booth in 2021 another individual reported dozens of dead bluebirds in a single nest box after the storm. Pauline did indicate, however, that before the storm, the population was quite strong, and she was hopeful that an increase in the quantity of nest boxes spread across Texas would help bluebirds rebound. TBS Newsletter July 2021

Based on my observations, preserving dead trees for natural nesting habitat is critically important for bluebirds. It’s my impression that when available, bluebirds might prefer a natural cavity such as an old woodpecker hole to a nest box. But bluebirds will also utilize nest boxes for roosting all year long and especially during cold weather. And as noted earlier, even though nest boxes and natural cavities benefit a number of native bird species, we hope that our work in providing and maintaining healthy nest boxes will encourage the return of Eastern Bluebirds to the property and will eventually help to restore the bluebird population that we’ve come to love at Jacob’s Well Natural Area.

If you are interested in learning more about how to construct, install, and monitor bluebird nest boxes, you will enjoy a companion article. Just scroll down below the photo and click the link on the right to read Bluebird Nest Box Management by Hays County Master Naturalist Bonnie Tull.

Project 702 RM Bluebird Nest Box Monitoring

Eastern Bluebird Sialia sialis

Black-crested Titmouse Baeolophus atricristatus

Bewick's Wren Thryomanes bewickii

Ash-throated Flycatcher Myiarchus cinerascens

Carolina Chickadee Poecile carolinensis

Carolina Wren Thryothorus ludovicianus