Nest Box Monitoring
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 generally need several new monitors each season. Monitoring the nests is enjoyable and rewarding. If you are interested in getting involved, contact the Bluebird Trail Coordinator.
Project NestWatch
All of the data collected from the Boulder County Audubon nest box trails is entered into Cornell University Lab of Ornithology Project NestWatch. This means that these data are not only accessible to scientists working to better understand avian biology but also to you! NestWatch provides many interactive tools to explore the data from maps to downloading the data. They also have many tools for learning more about building nest boxes designed for your area, identifying bird nests, and more. You can also participate in NestWatch on your own by becoming a certified NestWatcher.
A Short 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 nest box 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.
Bluebird Nesting Box Success Data
Male Mountain Bluebird. Blue feathers results from their structure, rather than from pigment. Because of this, the apparent color varies with the lighting.
Current Program, 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. 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.
Walker Ranch Nesting Data
2011 Season Overview
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.
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.)
Pictures from Boulder Audubon Nest Monitoring Activities
George & Marti Oetzel have monitored different trails over the seven years, and the picture collection below has benefitted from that variety. 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 animals seen and monitoring activities
Most of the pictures on this page are by George Oetzel and a few by Marti Oetzel; those contributed by others are labeled.
Navigation: 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.
Bluebird nesting activities
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.