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

Boulder County Audubon Society volunteers once again monitored nest boxes for bluebirds and other species in 2010. This was the sixth 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, 107 boxes total. 22 volunteers checked nest box status approximately weekly from late April to early August.

Spring 2010 was unusually cool and wet, which likely was a factor in an unusually large number of nest failures. White-breasted Nuthatches, in particular, built nests early in several places and suffered subsequent failures. There was also more nest predation than we have experienced in past years. As a result, fewer total birds fledged from the boxes in 2010 than in the past couple of years.

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 six 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 2010, so the species mix can reasonably be compared, even though there were significantly fewer birds fledged in 2010. In both 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, in both years, there were about 1.4 times as many WEBLs fledged on the lower trails as at Walker Ranch. Total chicks fledged on all trails in the two years were: 2009 — 67 MOBL and 262 WEBL; 2010 — 70 MOBL and 115 WEBL. There were a great many WEBL double clutches in 2009, none in 2010.

The graph on the right outlines  bluebirds fledging at Walker Ranch over the six 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.) Note that the number of MOBL chicks increased somewhat in 2010, which was a relatively bad year for the WEBL population.

Monitors record data about the nesting during the season that is then submitted to a national database maintained by Cornell University. Over 7000 nesting attempts have been reported to the database by Colorado monitors since 1997. Only Ohio and Pennsylvania have contributed more. Monitoring the nests is enjoyable and rewarding; find out more about what is involved.

Pictures from Boulder Audubon Nest Monitoring Activities
A good digital camera is a wonderful addition to monitoring and has yielded a large picture collection. 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
• Monitoring activties and other animals seen

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 MOBL perched on a snag above its box.	Male MOBL on a fence wire.	Male WEBL on branch.	WEBL pair inspecting box.	Female MOBL with nest material.
5 WEBL eggs.	WEBL hatching.	WEBL chicks in nest.	Male WEBL with food.	WEBL chick in a tree cavity. We sometimes find nests in places other than our boxes.
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.

Tree Swallow (TRES), indicated by the eye within the colored area.	Violet-green Swallow (VGSW), indicated by white around the eye.	Tree Swallow eggs.	WEBL eggs with one Violet-green Swallow egg, after contest for box. The WEBL eggs hatched and the chicks fledged. The swallow egg was buried in nest material after the WEBLs fledged.	Tree Swallow chicks in the nest.
Violet-green Swallows (VGSW) just hatched.	3 VGSW chicks.	VGSW mom "hiding" and leaving very young chicks exposed.	VGSW chick ready to fledge.	Tree Swallow at nest in a tree cavity.
Pygmy Nuthatch at box in Betasso.	Pygmy Nuthatch by self-made hole (by bird's feet).	White-breasted Nuthatch at box.	White-breasted Nuthatch feeding chicks in nest.	Feeding an ambitious chick at the hole.

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

Pasque flowers are among the first in the spring.	The ball cactus also flowers in April or early May.	Spring Beauties, also early and very small.	Sand Lillies, another early flower.	Mouse-ear Chickweed.
Wild Irises.	Narrow-leaf Penstemon.	A field of Penstemon on Shanahan Ridge.	Colorado Loco .	Early Larkspur.
Mariposa Lily.	Gaillardia with firemoths. The moths are Gaillardia specialists and camouflaged to be hard to spot on the flowers.	Beebalm, Betasso.	Photographing the thistles, the hummingbird was a surprise bonus.	Prickly Pear, late July or even August.
Boulder Raspberry, sometimes quite a large bush, numerous on Shanahan Ridge.	Leafy Cinquefoil.	Harebell, common at Betasso.	Wallflower.	Field of Bush Sunflowers at Betasso. Box 2 is on the tree.

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

Red Crossbill.	The pair of crossbills were in the same parking place at Betasso several weeks in a row.	Common Nighthawk in its daytime perch, Betasso.	singing Spotted Towhee.	Vesper Sparrow with food. They are numerous at both Walker Ranch and Betasso.
This Broad-tailed Hummingbird was perched on this twig every week.	Western Meadowlark with food.	Killdeer.	Dark-eyed Junco, Gray-headed race.	Clark's Nutcracker.
Northern Flicker feeding chicks at the nest.	Coyotes raised a family under one of the buildings at Walker Ranch.	White-tailed Deer.	Checking a nest box.	Note the hazy peak in the background. We hustled back to the car just as it started to rain.

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