Newsletter No. 2

Roosting boxes for overwinterizing bluebirds
Don Wills

The above normal temperatures of the last few winters continued in 1999-2000 allowing many Eastern bluebirds in the southern part of the province to overwinter successfully.
Both males and females were observed late in December along with an abundant supply of staghorn sumac. Thirty-nine nestboxes checked in late February contained various amounts of purple coloured manure from bluebirds eating sumac.

Only 3 Peterson boxes were used possibly due to the slanted floor, 2 Coker boxes contained large deposits and the standard NABS box with the flat floor were used by the rest.

Leaving boxes open over the winter can be a lifesaver for bluebirds as long as house sparrows are not found nearby. All roosting boxes were located near large sumac groves and some of these were the first boxes used in spring.

Weather – Bluebird Enemy No. 1

In the last 4 years, bluebird young and bluebird trail operators have suffered some miserable late May weather. 1997, 1999 and 2000 were killer years for my trail, while 1998’s perfect May, early June produced record numbers.

The holiday weekend of May 23, 2000 started cold and wet with very few noticeable insects. I lost 61 young over that weekend, most at the 6-7 day old stage. After nest failure, most of these adults started again in other boxes having only one successful nesting for 2000. Over the summer, conditions were normal with second broods starting quickly for pairs that had lucky early first nestings.

However, in early August, I noticed that in my area, the population of grasshoppers and other insects which are vital to bluebirds were in short supply. During this time several second brood nests were abandoned killing another 11 nestings. It was also the first year I can remember when 2nd brood females abandoned nests as soon as the young hatched.

Overall, the weather in 2000 made monitoring eastern bluebirds a difficult, stressful adventure, one that I hope is not repeated.

P.S. One insect that had a good season was the wood tick. Starting early in May, I removed more than 300 ticks from myself and the family dog!

Results for 2000 season Eastern Bluebird 340 nestboxes
105 pairs produced 532 fledglings.

Cowbird Parasitism

Fragmented woodlots in southern Ontario have enabled cowbirds to find the nests of many forest nesting species such as wood thrushes, veeries and wood warblers. I removed cowbird eggs from a veery’s nest in the most remote part of Backus woods – one of the largest tracts of Carolinian forest left in Ontario.

This year was the first time that I have had cowbirds entering bluebird boxes. Three tree swallows and 1 eastern bluebird nest contained cowbird eggs. The tree swallow boxes were the Peterson design with the slotted hole. The bluebird nesting was in a P.V.C. plastic design also with an oval entrance. After removing the intruder’s eggs, the tree swallows fledged, but the bluebird abandoned her 2nd brood clutch. Also Don Bull from Caledonia who uses all Peterson boxes with oval holes found early starlings were slipping through the entrances. He added panels with the 1½” entrance hole to solve this problem.

I would recommend that all boxes for bluebirds continue to use the standard 1½” round entrance to repel these avian intruders.