Boulder Audubon's Nest Box Monitoring Program

• Introduction
• The Bluebird Nesting and Monitoring Season
• Violet-green Swallows and Bluebirds
• Nuthatches at Work
• Flowers along the Nestbox Trails
• Other Animals seen while Monitoring Nests

Boulder County Audubon Society volunteers had another successful season of monitoring nest boxes for bluebirds and other species in 2008. The collaboration with Boulder County Parks and Open Space was expanded to include a second trail at Betasso Open Space and one at Heil Ranch, in addition to Walker Ranch/Meyers Gulch. A collaboration with City of Boulder Open Space and Mountain Parks began with the installation of boxes on Shanahan Ridge in 2007. Three additional nest box trails are planned for the 2009 season. The added trails will require more volunteers. Monitoring the nests is enjoyable and rewarding; find out more about what is involved.

In the 1980s, the Western Bluebird was considered "rare and declining" in Boulder County, meaning that there were fewer than 3 known nesting pairs. That is no longer the case, perhaps partly because of nest boxes at Walker Ranch and elsewhere in the county. (Current rare and declining list)

The table below summarizes bluebird fledging at Walker Ranch for 2005 through 2008. Not only are Western Bluebirds (WEBL) no longer rare, they have become the majority bluebird species in the park. A large part of the enormous increase of WEBL in 2008 is due to numerous cases of second broods in the same box. Research in Montana has shown a similar case of Western Bluebirds displacing Mountain Bluebirds and related it to aggressive male WEBLs. Another possible reason for the changing species ratio is the mix of nest sites at Walker Ranch. Western Bluebirds seem to prefer boxes in areas with large trees, while Mountain Bluebirds have remained more common in boxes on fence posts in open fields.

The Walker Ranch nests are at an elevation of about 7300 feet, so nesting is a bit later than in many parts of the country. The birds start building nests around the first of May and lay their first eggs in mid-to-late May. Once the first egg is laid, another is added each day, typically for three to five more days. Brooding starts when all the eggs have been laid, so that all will hatch on the same day, 12-14 days later. The chicks fledge 18 to 21 days after hatching.

While the focus of the program is bluebirds, other cavity nesters also benefit. At Walker Ranch, these included Tree Swallows, Violet-green Swallows, Mountain Chickadees, White-breasted Nuthatches, and House Wrens. The swallows start their nests later than the bluebirds, but there is enough overlap that there is often conflict over possession of nest boxes. Where we have noticed the conflict, we have sometimes added another box nearby. That leads to one species in each box and resolves the conflict.

In 2006, we saw a similar battle between Mountain Chickadees and Mountain Bluebirds. In this case, the chickadees had a head start but were being heavily harassed. When we installed another box nearby, it was occupied immediately by the bluebirds.

An experimental nest box trail was installed at the Betasso Open Space in 2006 and expanded to nine boxes for the 2007 season. Successful results during those first two years encouraged us to add an additional trail of 11 boxes in 2008.

Five boxes were installed late in the 2007 season near the Shanahan Ridge Trail, on City of Boulder Open Space. We knew at the time that we were probably too late for bluebirds to use the boxes. However, one box was used successfully by Violet-green Swallows, and we located a Western Bluebird nest in a snag near one of the boxes. A sixth box was added for 2008. One box had Western Bluebirds, two had Violet-green Swallows, and two had White-breasted Nuthatches.

Eight boxes at Heil Ranch in 2008 fledged 21 Mountain Bluebirds and 13 Western Bluebirds.

Pictures from the Bluebird Nesting and Monitoring Seasons
These pictures from the 2006 through 2008 seasons describe the bluebird nesting and monitoring season. Most of the photos are from Walker Ranch, with a few from Shanahan and Betasso labeled. Photos by George Oetzel.

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Some of the Audubon Society volunteers joined Denny Morris, of Boulder County Parks and Open Space, in April '06 to visit box locations changed since the '05 season.	Male Mountain Bluebird perched on fence near box.	Female Mountain Bluebird. Nice pose near a box with chicks. (6/8/07)	Tree Swallow at nest hole in tree.	Tree Swallows also use the boxes. They nest later than the bluebirds and sometimes move into a box after the bluebirds have fledged.
Female Mountain Bluebird with food. (6/14)	Female Mountain Bluebird checking on the box. After the box has been opened for monitoring, they often perch briefly to check before re-entering the box. (5/26)	Female Mountain Bluebird with nesting material. (4/23)	Monitoring a box that opens in the front.	View of one box location at Betasso
six Mountain Bluebird eggs just after the first has hatched.	Chicks at 2 or 3 days of age. (6/14)	Western Bluebird chicks, perhaps 10 days after hatching.	Western Bluebird nestling nearly ready to fledge from natural cavity at Shanahan Ridge. (7/9/07)	Mountain Bluebird 3 to 4 weeks after fledging. (7/18/07)
Western Bluebirds checking a box inside and out before starting a nest. (4/21)	Male Western Bluebird with food for nestlings. (7/10/07)	WEBL chick ready to fledge, perhaps reluctant.	Used Nest. They're not neat!	This Mountain Bluebird found a nest hole in a power pole

Violet-green Swallows and Bluebirds
We have seen numerous instances of conflict over nesting sites between Violet-green Swallows (VGSW) and both bluebird species. This has included VGSW entering a box where we had just found a bluebird hen sitting on eggs. In another case, we found a VGSW looking out of a box where we expected that Western Bluebird (WEBL) chicks were near fledging. A later check of that box revealed 5 WEBL eggs (a second brood) and one VGSW egg. The WEBLs later fledged, and the VGSW egg failed to hatch.

Violet-green Swallow at Shanahan Ridge. The Violet-greens have become more common than the tree swallows in the past few years.

Violet-green Swallow hatchlings.

Violet-green Swallow hen exposing chicks.

Violet-green Swallow chicks waiting for food. The parent feeds without landing. These chicks should fledge within a day or two of this picture. (7/28)

Violet-green Swallow leaning out of WEBL nest box.

5 WEBL eggs surround one VGSW egg that didn't hatch.

Nuthatches at Work
White-breasted Nuthatches sometimes use the boxes. Pygmy Nuthatches have as well, although here we caught pictures of one making its own cavity.

White-breasted Nuthatch Chick. Where's Mommy?

Mommy nuthatch arrives with food.

Feeding the chick.

Feeding others in the nest.

Pygmy Nuthatch by its hole.

Pygmy Nuthatch excavating in the hole.

Flowers along the Nestbox Trails
The nesting season is also the season of spring wildflowers. Here is a sampling of those we spotted while visiting nest boxes. If not specified, pictures are from Walker Ranch. Photos by George Oetzel.

Ball Cactus visited by a bee. (5/2)	Sand Lily (or Star Lily). (5/2)	Wild Geranium. (5/26)	Gaillardia (Blanketflower) with 2 firemoths. The moths are Gaillardia specialists. Their coloration provides excellent camouflage, especially when they are carefully aligned with the flower's colors. (6/14/06) Only a single firemoth was spotted in the 2007 season.	Lilacs near Walker Ranch buildings. (5/25)	Spring Beauty. (5/2)
A forest of penstemon, Shanahan Ridge (5/24)	A small wild rose. (6/21)	Mariposa Lily. (6/29)	Narrow-leaved Penstemon. (6/21)	Wallflower, Betasso (6/1)	Prickly Poppy, Betasso (7/4)
Irises. (5/26)	Early Larkspur. (5/17)	Pasque flowers are among the earliest to bloom. (4/23)	Mouse-ear Chickpea, also goes by a number of other names. (5/25)	Prickly Pear Cactus, Betasso. (7/4)	Whisk-broom Parsley. (5/26)

Other Animals and seen while Monitoring Nests
The nest boxes are sometimes used by other birds, as well as the two species of bluebirds. Other animals also pass by sometimes during the monitoring days. Photos by George Oetzel.

There was a coyote den under one of the buildings. We didn't see the pups, but we did get a nice look at this coyote passing by.	Mule Deer are fairly common at Walker Ranch, although not usually this close by.	Other birds also nest at Walker Ranch without occupying our nest boxes. Here a mother Northern Flicker feeds her chicks. (6/14)	The Dark-eyed (Grey-headed) Junco probably nested at higher altitude.	There was a male Broad-tailed Hummingbird on this twig almost every time we passed in both the 2006 and 2007 seasons. The males don't help raise the brood. The perch was also used in the '08 season, perhaps by the same bird.
Meadowlark with food for chicks in an unknown nest location. Meadowlarks nest on the ground, and don't use the nest boxes. (6/29/07)	Singing Green-tailed Towhee	Song Sparrow, Walker Ranch.	This Lark Sparrow probably was a transient visitor, nesting elsewhere.	Seeing deer while monitoring at Betasso is quite common.
Male Red-winged Crossbill. Crossbills are spotted occasionally. They aren't cavity nesters; none of the volunteers have spotted nests or adults feeding young.	Common Nighthawks fly into Betasso early in the morning to roost for the day.	We were surprised to find the Clark's Nutcracker in Betasso, only a little above 6000 feet.	Although it's conceivable that the Killdeer might nest at Walker Ranch, its nest more likely would be nearer a body of water. There are lakes within a few miles.	Vesper Sparrows are very common throughout the season. This one is waiting to take food to a chick. We didn't locate the nest. (6/20/07)

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