by Leslie Palmer

Columbia Audubon Nature Sanctuary (CANS) and Bonnie View (BV) Nature Area provide protection for plants and animals that live there as well as nature viewing for visitors.  Nest boxes provide additional nesting sites as green space shrinks and urban areas expand.  CANS/BV supports 14 nest boxes that are monitored weekly.  The North American Bluebird Society publication “Bluebird” Spring 2024, Vol. 46, No. 2 suggests that the Eastern Bluebird (EABL) populations vary across ranges.

The 2024 nest box weekly monitoring began February 20 with a walk-through to assess nest box and habitat maintenance required for this nesting season, which began approximately the second week of March.  The last week of February monitoring included brush removal and weeding underneath and around nest boxes as well as the approach to the boxes.  Nest boxes were opened, brushed, cleaned and assessed for needed upkeep (screws tightened, wasps and/or ants as well as grass and wood shavings were removed.)  Five nest boxes showed evidence of Eurasian House Sparrow (HOSP) nests, which were removed and destroyed.

This season, all nest boxes were used except one (CANS 7).  One nest box contained one dead baby EABL; two nest boxes were used by EABL within one to two weeks of having previously fledged; 4 blue eggs were robbed from one EABL nest while 5 white eggs were robbed from another EABL nest.  The eggs were taken with no other sign of disturbance suggesting a black snake or possible human involvement.  Additional predation comes in the form of weather/climate, loss of habitat, raccoons, cats, etc.  The final count for the 2024 season indicates that 56 EABL eggs were laid (5 were white), there were 11 successful nesting attempts which generated 46 fledglings.  The Black-capped Chickadees (BCCH) laid 18 eggs in three attempts generating 18 fledglings.  Last year, the 2023 season produced 45 EABL eggs laid and 44 fledglings in 9 successful nesting attempts.  BCCH’s laid 12 eggs and fledged 12 chicks after two successful nesting attempts.  The House Wren’s (HOWR) produced 19 eggs in three successful attempts and fledged 13 young.

The HOSP is a non-native bird that was brought to the Northeast coast of the US in the mid-19^th century, according to the above-mentioned publication (page 9).  The HOSP is an aggressive species that multiplies quickly (may nest as many as four times in a season), destroys and overtakes nests of other species and will even kill an adult bird in competition for a nesting site.  This season alone, HOSPs moved into two separate nest boxes to build nests on top of already existing BCCH nests.  In 2020, a HOSP attacked the nest of an EABL poking holes in each of the four blue eggs.  The HOSP poses a serious threat to other bird species as well.

Routine weekly monitoring of these 14 nest boxes involves removing HOSP nests, recording the species and number of full nests found.  The number of eggs laid, young birds viewed in each nest box and number of young birds fledged, the number of nesting attempts, the number of failed attempts and successful attempts is all reported the last week of August to the Missouri Bluebird Society, that reports the findings to the North American Bluebird Society database.  Retired nests are removed as soon after fledging as possible and treated for ants, wasps, bacteria, etc. to make ready for the next nesting attempt.

CANS/BV offer visitors bird viewing and education in a natural setting surrounded by native plants, which provide food and habitat for numerous birds, insects (especially butterflies) and other animals in a pleasing landscape.  It is our good fortune to monitor nest boxes once a week during the summer months at CANS/BV.  Monitoring nest boxes can be filled with surprises (good and bad), so it is good to try to be prepared for the unexpected.  We are excited to be a part of helping bluebirds survive and thrive. Master Naturalists (Boone’s Lick Chapter)

Kitty Peer, Leslie Palmer and Pat Smith