WINTER 2001/VOLUME 15, NUMBER 1
by Tina Phillips
Low numbers of nesting
attempts by cavity-nesting birds spur conservation agenda
Since 1997, The Birdhouse Network (TBN) has developed annual
"Top 10" lists of the most commonly reported cavity-nesting
birds. With little variation, the usual suspects always appear
- Tree Swallows, Eastern Bluebirds, House Wrens, House Sparrows,
Mountain Bluebirds, and Western Bluebirds. This year was no exception,
but for the first time, we looked at nesting attempts of cavity-nesting
birds from the bottom of the list. In total, there are 16 species
for which TBN has fewer than 50 recorded nesting attempts over
a four-year period (Table 1). Because
of the low numbers of nesting attempts in our database, we have
termed them "TBN's Most Wanted List."
Why do we have so little data on these species? Are they truly
rare? Are their habitats too remote for nest-box monitors to
access? Are they finding enough natural nest sites in the wild,
eliminating the need for nest boxes? Or are nest-box monitors
simply not trying to attract them?
| During the last 20 years, monitoring programs such as The Birdhouse Network have, in part, helped birds of "conservation priority" rebound from population declines. The Eastern Bluebird, for example, has benefited greatly from the concerted efforts of people setting up nest boxes during the last 40 years. It is likely that our Most Wanted List birds might also benefit from the efforts of nest-box monitors if we focus our attention and attract them to suitably placed nest boxes. The simple action of placing nest boxes for less- common species presents an ideal opportunity for citizen scientists to initiate a proactive approach to conservation. If TBN's Most Wanted List species are truly experiencing population declines, then as nest-box monitors and environmental stewards, we should take special notice of them and promote a conservation agenda.. |
|
To determine whether some of our less-reported species are actually as rare as they appear, we looked at long-term population monitoring databases. The U.S. Geological Survey Patuxent Wildlife Research Center <http://www. mbr.nbs.gov/> offers a wealth of information on surveywide population changes of bird species as recorded by the North American Breeding Bird Survey (BBS). The left half of Table 1 shows TBN's Most Wanted List, along with their numbers and percentage of total nesting attempts in our database. A nesting attempt was defined as the presence of at least one egg laid in the nest. In 16 of these species, less than 0.5 percent reported nesting attempts; combined, they make up only 2.5 percent of TBN's entire nesting attempt records. The right half of the table depicts the BBS species population change per year over the last 19 years, number of routes surveyed, and significance of the change. In all, 9 of our 16 Most Wanted List birds show population declines, with 6 of the 9 showing statistically significant declines. The remaining 7 species show either a significant or nonsignificant increase. Interestingly, the Western Bluebird and the Carolina Chickadee are listed as having significant declines by the BBS, but they don't make our Most Wanted List, because they constitute 4.5 percent and 2.4 percent of all reported TBN nesting attempts, respectively. Given their BBS population changes, however, we will keep a close eye on Western Bluebird and Carolina Chickadee data in the future.
We are in no way implying that these 16 species are experiencing population declines based on the fact that TBN has few data on them. The TBN database, although not able to determine whether populations are changing, can help to diagnose why populations are changing through analysis of nesting success data. With continued data collection by TBN participants, we can acquire the amount and kind of information necessary to analyze why cavity-nesting bird populations are increasing or decreasing.
To obtain more data on these priority birds, The Birdhouse
Network will begin a concerted conservation effort aimed at educating
nest-box monitors about their nesting requirements and encouraging
participants to erect homes for them. TBN's Most Wanted includes,
but is not limited to, all of the birds listed in Table
1. Whenever possible, we will spotlight a rare TBN cavity-nester
in future issues of Birdscope and describe habitat, range, and
special nesting and nest-box requirements. We will give priority
to the secondary cavity-nesters (which readily use nest boxes)
that show declines in the BBS database. For many of these priority
species, our information about breeding biology is scanty at
best. Nest-box monitors who provide special requirements for
these birds will not only add valuable information to science,
they may help promote the conservation of these less-reported
species. We hope these efforts will increase the diversity of
our database and our continent as well.
When possible, The Birdhouse Network will spotlight a rare
cavity nester, such as the Purple Martin, in future issues of
Birdscope.
photo by Lang Elliott