On February 24th, the Greater Princeton Branch of AYLUS (GPA) Environment Committee gladly took a volunteer bluebird nest box monitoring opportunity offered by the Mercer County Park Commission.
The Eastern Bluebird is a formerly threatened bird species that has made a tremendous comeback because of the efforts of amateur conservationists throughout the United States. Mercer County Park Commission staff and volunteers aid the nesting of bluebirds and other native bird species by monitoring boxes for nesting attempts by non-native birds.
The Mercer County Park Commission has five bluebird box monitoring locations available. One is at the Mercer Meadows Pole Farm (Lawrence/Pennington), two are at Mercer Oaks Golf Course (Hamilton/West Windsor), one is at Mountain View Golf Course (Ewing), and the last is at Mercer County Park (Hamilton/West Windsor). Monitoring is typically a 2 hours/week commitment from about March through July. New monitors will need to have a 15-30 minute training.
WHY Monitor a Bluebird Nest Box?
It is very important that bluebird nest boxes be actively monitored (checked) at least once a week. Bluebirds are tolerant of humans, and will not abandon a nest box that is properly monitored. All bluebird boxes should be built so that they can be opened either from the side, front, or top.
A box that is not monitored may do more harm to bluebirds than good. Monitoring increases the chances of success for bluebirds using the box. When good records are kept, it is also valuable for determining population trends. Monitoring nest boxes will alert you to problems birds may be having with predators and competitors. House Sparrows (sometimes called English Sparrows) and European Starlings are non-native species introduced from Europe. Their aggressive seizure of cavity nest sites is a primary reason for declines in bluebird populations. Starlings nest in many of the natural nest sites but can be excluded from nest boxes by using 1½ or 1⁹⁄₁₆ inch entrance holes. House Sparrows are smaller, so they can readily enter bluebird nest boxes. They frequently kill adult and nestling bluebirds, destroy their eggs, or drive them from their nests. At no time should they be allowed to successfully nest in bluebird boxes. Doing so will increase the House Sparrow population and further reduce the number of bluebirds. See the NABS factsheet on House Sparrow Control (available on our website at www.nabluebirdsociety.org/bluebirdfacts.htm).
A paper wasp or mouse nest will drive nesting birds away from the box, and should be removed. Take appropriate precautions to avoid breathing the dust from a mouse nest. Knowing what species is using the box is also beneficial. Bluebird societies would like you to monitor and report all species using your nest boxes, not just bluebirds. Tree Swallows, titmice, chickadees, Carolina and House Wrens and nuthatches are all native, beneficial birds. Remember: It is illegal to remove an active nest of any native cavity-nesting bird. Keeping records on a weekly basis and sending survey forms in at the end of the nesting season increases our knowledge of cavity-nesting birds.
After any nesting effort has ended, either due to nest failure or successful fledging of the young, remove the used nest from the box. When a bluebird nest is successful, re-nesting in the same box may be encouraged if the first nest is removed. This can be done as soon as all chicks have left the nest. Females usually build a new nest.
WHAT TO MONITOR
When you monitor a box, determine which species is using it by examining nesting material and eggs. Record the date and the number of eggs or young observed. Knowing when the eggs were laid will help you determine if they are infertile, or when they should hatch and when the young would be expected to leave the nest. In the case of most cavity nesters, one egg is laid one each day until the entire clutch is complete. Incubation will then begin. For bluebirds, incubation typically lasts approximately 12–14 days. After hatching, the chicks will remain in the nest for about 17–21 days. Your monitoring should be limited to viewing from a distance after the 12–13th day, or the chicks might jump or fly from the box prematurely.
HOW TO MONITOR
Nest monitoring should only be done during calm, mild, and dry weather conditions to reduce the chance of chilling chicks or eggs. Open the nest box carefully and do not allow the eggs to fall out or chicks to jump out. Songbirds have a poor sense of smell and will not abandon the nest due to monitoring the nest, eggs, or chicks. Even so, you should avoid touching eggs or nestlings.
Complete monitoring as quickly and quietly as possible to minimize disturbance. Avoid disposing of used nest material near the nest site as it may attract predators—instead put it in a paper or plastic bag and dispose of it in the trash far from the nestbox. Always be certain to close the box door securely before leaving. Record what you observed.
