Boulder Audubon's Nest Box Monitoring Program
Web page composition by George Oetzel.

Boulder County Audubon Society volunteers once again monitored nest boxes for bluebirds and other species in 2011. This was the seventh year of collaboration with Boulder County Parks and Open Space (BCPOS) and the fourth year of collaboration with the City of Boulder Open Space and Mountain Parks (OSMP). With three new trails added in 2009, the program has grown to 11 trails of 6 to 13 boxes each, 106 boxes total. 22 volunteers checked nest box status approximately weekly from late April to early August.

Although it’s often referred to as a bluebird program, several other species also use the boxes. The goal is for every box to be checked and data recorded approximately weekly from May through July. Weekly recording assures that the number of eggs and hatched chicks are known, so that nesting success can be evaluated and yield an accurate count of the number fledged. Data are submitted to a national database maintained by Cornell University in September or October. Although many monitors return year after year, we expect to need several more for the 2012 season. Monitoring the nests is enjoyable and rewarding; find out more about what is involved.

Over 7000 nesting attempts have been reported to the database by Colorado monitors since 1997. Only Ohio and Pennsylvania have contributed more. (Denver Audubon has one of the largest monitoring programs in the U.S.)

A Little History of Boulder County Nest Monitoring

In the 1980s, the Western Bluebird was considered "rare and declining" in Boulder County, meaning that there were fewer than 3 known nesting pairs. (Current rare and declining list) In the seven years of the Boulder Audubon program, we have seen a dramatic increase in Western Bluebird (WEBL) nests and a slight decrease of Mountain Bluebird (MOBL) nests.

Walker Ranch has the longest history of nestbox monitoring in Boulder County. The table below shows the bluebird nesting recorded in 1989-91 and 1995, the few years for which there are reasonably good records. A single WEBL nest was recorded in 1989, none in the other years. Although people seem to have looked at boxes in the late '90s, they didn't produce useful nesting records. There may have been more box use by WEBLs during 1996-2004, but there are no records.

Current Program Results, beginning 2005

More boxes were added at Walker Ranch in 2005, so 46-48 boxes have been monitored there in the years since. Those boxes average about 7250 ft elevation, mostly mounted on trees with much open, grassy area around them. Additional trails were added in various county and city open space areas beginning in 2007. Those trails are generally lower, averaging about 6350 ft and mostly in areas with a higher density of trees. As a result of these differences, the mix of MOBL and WEBL nests differs substantially between the Walker Ranch trails and the newer trails.

The two sets of trails had only very minor changes between 2009 and 2011, so the species mix can reasonably be compared, even though there were significantly fewer birds fledged in 2010. In those years, there were approximately 3.5 times as many MOBLs fledged at Walker Ranch as on the lower trails, even though the lower trails have almost 50% more boxes. Correspondingly, there were about 1.4 times as many WEBLs fledged on the lower trails as at Walker Ranch. Total chicks fledged on all trails for 2008-2011 are shown in the table below. There were a great many WEBL double clutches in 2009, none in 2010, and just one in 2011.

The graph on the right outlines bluebirds fledging at Walker Ranch over the seven years of the current Boulder Audubon monitoring effort. In 2005, there were still only 8 WEBL nests at Walker Ranch. The increasing number of WEBL nests in the first 3 years is probably a result of returning birds and the larger number of available boxes. The huge increase of WEBL chicks in 2008 is due to 11 double clutches. There is a suggestion in the 2008-10 results that competition with WEBLs has reduced the MOBL success. (Similar observations have been reported elsewhere.) However, the number of MOBL chicks has been rather stable for the past three years.

As the table below shows, overall results vary considerably from year to year. There are always some boxes that remain unused, while others have two nests, the second after chicks have fledged from the first. In both 2008 and 2009, favorable weather allowed an early start to the nesting season, so there were many cases in which the same pair was able to produce two clutches of chicks in one box. In 2010 and 2011, the weather was less favorable in the early season. In addition, there was more predation of boxes in the 2010 season than we have seen in any other year, apparently due to snakes.

Pictures from Boulder Audubon Nest Monitoring Activities
George & Marti Oetzel have monitored different trails over the seven years, and the picture collection has benefitted from that variety. This year, we have added a few pictures by other monitors. The pictures are divided into 4 categories:

• Bluebird nesting activities
• Other bird species using boxes and in the area around them
• Flowers at Walker Ranch and Betasso
• Other birds and animals seen, ans some monitoring activities

Most of the picures on this page are by George Oetzel and a few by Marti Oetzel; those contributed by others are labeled.

In each group, click to expand pictures, click on expanded to return to thumbnail. You can also use arrow keys to move to next/previous expanded picture.

This first group features Mountain Bluebirds (MOBL) and Western Bluebirds (WEBL). There is great demand for the boxes among returning adults and chicks. We occasionally spot bluebird nests in cavities in trees or poles, made by woodpeckers or sometimes broken limbs. There have been a few reports of Eastern Bluebirds nesting in Boulder County, but none so far in the boxes we monitor.

Male Mountain Bluebird (Sue Olmsted photo).	Male Western Bluebird.	Bluebird pair checking box in April, Meyers Gulch.	Western Bluebird at box.	Female Mountain Bluebird with nesting material.
Mountain Bluebirds started a nest in the grill at Betasso. We closed the grill entrance and put up boxes nearby.	The "grill birds" nested successfully in the nearby box. Here, the male bringing food.	Mama Mountain Bluebird brings food to the box.	Bluebird eggs in nest.	We caught the first egg hatching.
Newly hatched birds have some fuzz that will later become feathers.	These chicks are a few days old.	As the feathers grow, the chicks are always hungry.	Western Bluebird with a tasty bug for the chicks.	Mountain Bluebird brings a bug to the vicinity of the nest.
Usually the hen leaves the box when it is opened. Sometimes the urge to protect the chicks is so strong that she just moves to the back of the box and refuses to leave. This can make it challenging for monitors to count the chicks.	Recently fledged Mountain Bluebird, Walker Ranch.	Recently fledged Mountain Bluebird on a small tree.	Bluebird fledgling at a small Walker Ranch pond.	Bluebird chick looking out from a nest in a snag, Shanahan Ridge.
MOBL pair after we closed entry to nest start in the grill at Betasso. We added boxes nearby to give them the alternative shown in the next pictures.	Female MOBL at box substituted for grill nest.	Male MOBL with food for chicks in substitute box.	WEBL chick after fledging.	MOBL chick on a mullein.

Violet-green Swallows (VGSW) and Tree Swallows (TRES) are the most common other species that use our nest boxes. Other sometime users include White-breasted Nuthatches (WBNU), Pygmy Nuthatches (PYNU), Mountain Chickadees (MOCH) and House Wrens (HOWR).

Tree Swallow on a snag.	Violet-green Swallow.	Tree Swallow with nesting material at a box, Meyers Gulch.	Violet-green Swallow eggs.	Tree Swallow eggs. The color difference between the two swallow species egg pictures is probably due to lighting, rather than actual color.
Violet-green Swallow hatchlings.	Hungry chicks anticipating food. This is sometimes the reaction when monitors open the box.	Last Tree Swallow chick is ready to leave the box, Betasso.	Tree Swallow at nest cavity in a tree, Betasso.	We watched this Pygmy Nuthatch excavating its nest hole.
Pygmy Nuthatches also use nest boxes. This one, at Bald Mountain, raised 10 chicks.	White-breasted Nuthatch delivering food to an older chick.	Newly hatched White-breasted Nuthatch chicks. (Catherine Labio photo).	Same White-breasted Nuthatch chicks six days later. (Catherine Labio photo).	A few Mountain Chickadees also use our nest boxes each year.

One of the pleasures of monitoring the nest boxes is watching the changing flowers as the season progresses.

Pasque flowers are among the earliest of the season, usually in April.	Ball Cactus with a bee in early May.	Spring Beauties in early May.	Sand Lillies in late May.	Mouse-ear Chickweed, late May.
Wild Iris cluster, late May 2006. Iris blossoms were scarce and late in Meyers Gulch in 2011.	Light Iris, Meyers Gulch, late July 2011.	Narrow-leaved Penstemon, June.	Forest floor covered with Penstemon at Shanahan Ridge, late May.	Colorado Loco and Sulphur Flowers, June.
Mariposa Lily (Sego Lily) August.	Gaillardia with Firemoths, specialists that are camouflaged to match the flower. Walker Ranch, June.	Variable Checkerspot butterfly on Gaillardia, Walker Ranch, June.	Beebalm at Betasso, July.	Wild Geranium, June.
Boulder Raspberry, June.	Leafy Cinquefoil, June.	Harebell, June.	Early Larkspur, early June.	Golden Banner, June.
Green Gentian, Shanahan Ridge, May.	Miners Candle, Meyers Gulch, June.	Prickly Poppies, Betasso, late June.	Prickly Pear Cactus, Betasso, July.	Field of Common Sunflowers at Betasso, June. The tree has a nest box.

This last collection of pictures includes some birds that don't use our boxes, other animals, and monitoring activities.

Broad-tailed Hummingbird, Walker Ranch. The bird was perched on this branch every week during the monitoring season.	Two Red Crossbills in the Betasso parking lot.	Common Nighthawk on its daytime perch at Betasso.	Williamsons Sapsucker at nest hole in Meyers Gulch.	Song Sparrow.
Red-headed Wookpecker, Eldorado Mt, 2011.	Killdeer, Walker Ranch.	Gray-headed Junco.	Northern Flicker feeding young in Meyers Gulch.	Western Meadowlark with food for chicks.
Vesper Sparrow with a bug.	Deer watching the nest box monitors. See the next picture for the bird on the deer's back.	Cowbird on the deer.	Coyote, Walker Ranch.	Mule Deer, Walker Ranch.
Warning sign along the trail in Meyers Gulch. Nobody has reported seeing a Mountain Lion while monitoring. Bears, however, have been seen occasionally.	Visiting a box in Meyers Gulch.	Checking a box at Walker Ranch.	Checking a box at Heil Ranch.	This box was destroyed by a bear. This happens about once a year on one or another of the trails.

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