About Eastern Bluebirds

Author: Bill Read

Introduction

The Eastern Bluebird is a cherished sight for birdwatchers across its range in Ontario. It held a special place in the folklore of our early settlers who welcomed it as a true harbinger of spring. Its colourful appearance and distinctive calls make it easily recognizable. The Eastern Bluebird breeds throughout the province except in the Hudson Bay lowlands. It is found in a variety of habitats from apple orchards to boreal forest, and will nest in almost any area with short vegatation as long as suitable nest cavities are available.

Breeding Biology

Most nests in Ontario are found in nest boxes, natural cavities, old fence posts and tree branch stubs. Nests are relatively easy to find because of the bluebirds habit of searching for food from overhead perches and by its distinctive call which is easily recognizable. Bluebirds frequently (but not always) make distress calls when a nest site is approached. In Northern Ontario bluebirds are found in timber clear cut areas and forest fire burn areas where they nest in trunk and branch stubs. Heights of 97 nests in natural sites ranged from 0.6 to 18 m (2 to 60 feet) with 49 averaging 1.4 to 3.7 m (4.5 to 12 feet). [Peck and James]

In Southern Ontario most bluebirds migrate west along the north shores of Lake Ontario and Lake Erie until they cross over into Michigan. On Oct 27, 1991, 825 Eastern Bluebirds were recorded as they migrated past Holiday Beach near Windsor. In Northern Ontario bluebirds migrate west along the north shore of Lake Superior until they reach Minnesota. In the fall of 2001 Thunder Cape Bird Observatory recorded 740 bluebirds during migration. Since 1985 more and more bluebirds have been overwintering in Ontario mostly in Carolinian areas inland from lakes Ontario and Erie. During the 2002 Christmas Bird Counts in Ontario 779 Eastern Bluebirds were recorded. With global warming this trend should continue.

The Eastern Bluebird breeds throughout the province in a wide variety of habitats, forest clear cuts, forest fire burn areas, agricultural areas adjacent to urban centres, fallow fields, grazed pastures, fruit orchards or almost any open area with short grass and suitable nest cavities. It eats mostly insects during the breeding season with fruit forming a small part of its diet in late summer especially when feeding young. Bluebirds nest individually or in loose colonies where suitable habitat exists. Egg dates from April 10 to September 2 [Peck and James] and from March 27 to August 11 [Risley]. Barry (1970,1974) reported a range of 1-6 egg clutches in the Oshawa-Lake Scugog area, with average number of eggs laid per attempt ranging from 4.01 to 4.45 from 1967 through 1971. Confirmed breeding can be established by seeing fledged young with adults which stay close by as adults renest.

Distribution and Population Status

At the time of the first Ontario Breeding Bird Atlas (1981 – 1985) the Eastern Bluebird was found in all areas of the province except the Hudson Bay lowlands. The major concentration of the species was found along the southern edge of the Canadian Shield (Simcoe Rideau area). The second Ontario Breeding Bird Atlas (2001 – 2005) showed significant increases in all areas with the largest increases in the Carolinian area (39%) and the Simcoe Rideau area (38%). This represents a 69% increase in the number of squares occupied between atlases. BBS data showed a decline (% change per year) of 1.072% from 1966-1978 and an increase of 11.895% from 1978-1987 [Sauer and Droege 1990]. Overall from 1968-2005 BBS data indicate an annnual increase of 6.5% [Sauer and Droege 2006].

Weather has always been the primary limiting factor contributing to Eastern Bluebird population declines but these declines were followed by rebounds to former levels within a few years. Beginning in the early fifties these rebounds appear to have failed. Well managed predator proof nestbox trails now provide a means for successfull rebounds. Warmer weather both of average temperature and a decline in the number of cold days -15c or below have meant that more eastern bluebirds are able to survive the winter and return to breed [Phillips 2006].

The formation of the North American Bluebird Society in 1978 and the Ontario Eastern Bluebird Society in 1988 also contributed to the increase in numbers by encouraging thousands of individuals and groups across North America to put up nestboxes for Bluebirds. The Eastern Bluebird was declared rare by COSEWIC and MNR based on its low population following the severe winters of 1976 to 1978 [Risley 1987]. The population has increased significantly since to a point where it was delisted in 1996 based on a COSEWIC report [Read and Alvo]. Due to the ease of detecting this species the atlas map is an accurate depiction of its breeding distribution. 

Abundance

The relative abundance map shows a fairly even distribution throughout most of Southern Ontario with a general decrease northward with the lowest numbers in the southern and northern shield areas. Areas of higher density in Northern Ontario are closely associated with pockets of agriculture adjacent to urban centres such as Cochrane, Sault Saint Marie, Thunder Bay and Rainy River. This distribution generally reflects a scarcity of suitable habitat although bluebirds nesting in timber clear cuts and forest fire burn areas could be missed because of a lack of atlas coverage. Suitable habitat exists in many areas of Ontario but a lack of suitable nest cavities may prevent it from occupying these areas.

Point counts revealed that abundance was greatest south of the shield in the Simcoe Rideau and Carolinian areas. Higher densities are almost always correlated with areas that have well managed predator proof nest box trails. An estimate of 2-10 pairs per square with breeding evidence in 1237 squares would represent a range of 2474 to 12370 pairs of Eastern Bluebirds in Ontario at the end of the breeding season in 2005. Highly volatile weather attributed to global warming will result in a fluctuating bluebird population in the future.

Listen to Eastern Bluebirds

Bluebird Range Map

For an interactive species map, go to: www.birdsontario.org/atlas/map.jsp. Select “Eastern Bluebird” from the “Select a species” drop-down list and click on “Display map”.

References

Barry,D. 1970 The Eastern Bluebird in the Oshawa-Scugog area. ONT. Bird Banding.6[2]:39-51.

Barry.D. 1974. Eastern Blubird Nestbox Project. Appendix F pp 347-354 in R.G. Tozer:J.M.Richards. Birds of the Oshawa-Lake Scugog Region. Alger.Press. Oshawa.

Peck.G.K and R.D James. 1987 Breeding Birds Of Ontario.Nidiology and Distribution. VOL 2:Passerines.Royal. ONT. Museum.Life Sci. Misc. Publ., Toronto.

Phillips David, Senior Climatologist, Environment Canada Weather Office personal communication.

Read,W.F and R Alvo. 1996 Updated status report on the Eastern Bluebird in Canada.

Risley C.J. 1981. The Status of the Eastern Bluebird (Sialia Sialis} in Canada with particular reference to Ontario. Nongame Program, Ontario Ministry 0f Natural Resources.

Risley,C. 1987. Eastern Bluebird in Cadman, M.D.,P.F.J.Eagles and F.M.Helleiner eds. 1987. Atlas of the Breeding Birds of Ontario.Waterloo: University of Waterloo Press.617 pages.

Sauer,J.R. and S. Droege. 1990. Recent Population Trends of the Eastern Bluebird. Wilson Bulletin 102 [2]: 239-252.

Sauer,J.R. and S.Droege. 2006. Recent Population Trends of the Eastern Bluebird.

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