Eastern Bluebird (Sialia sialis) Ben Pinkowski
Kensington Metropark, Livingston Co., MI (Click to view a comparison of Atlas I to II) 6/13/2009 © Jim Ridley This species sponsored in honor of Virginia Tisdale Distribution One of our most popular and often-watched Before the late 1800s, Eastern Bluebird distribution was generally believed to be limited songbirds, the Eastern Bluebird is a fairly to tree-fall and fire-maintained mature oak-pine common summer resident around open openings in the eastern deciduous forests woodlands and fields, especially where nest box (Pinkowski 1977, Gowaty and Plissner 1998). projects have been placed for its benefit. Winter Although bluebirds require relatively open occurrence in the state is unpredictable and habitats containing few scattered trees and largely dependent on fruit supplies and the shrubs for breeding, fruit-bearing shrubs such as severity of the season. The bubbly, cheery song sumac are important early in the nesting season of colorful male bluebirds during March is and during non-breeding times. generally regarded as an unmistakable sign of spring. By mid-April or May the females have Historically, bluebird breeding numbers across settled into incubation duties and soon both the state were probably highest during post- adults are busy feeding young. Multiple broods lumbering times in the early 1900's, but dropped are common, so the entire bluebird nesting markedly after nest cavity competitors such as season can be lengthy and pairs can be found the European Starling and House Sparrow with nests from March until late August, a arrived. Changes in agricultural practices, period spanning nearly half a year. In reality, especially widespread use of pesticides in the both the bluebird's early arrival and its long mid 1900s caused further decline, which nesting season are rooted in intense competition persisted until nesting box projects became with other hole-nesters for limited nesting popular in the 1960's and 1970's. The continued cavities, and the bluebird's ability to survive popularity of nest boxes is generally thought to other forms of environmental adversity. Indeed, be responsible for the bluebird’s current the species’ current broad distribution through abundance, although natural cavities created by Michigan represents a welcomed recovery from woodpeckers in dead or diseased woodlands low population levels throughout its range in may contribute locally (Pinkowski 1976). eastern North America during the mid-1900s.
© 2011 Kalamazoo Nature Center Eastern Bluebird (Sialia sialis) Ben Pinkowski
Foraging bluebirds utilize fences, wires, and (Pinkowski 1979). Both parents feed the young, exposed tree limbs as perches to locate their though male involvement usually begins to prey, which is typically seized on the ground. decline during July and especially August. The Short, sparse ground cover vegetation is nestling period is long, sometimes reaching preferred, and extensive areas with tall upwards of three weeks if the nestlings are agricultural crops lacking perches are always undisturbed. Bluebird family groups are more avoided. Large nesting territories are needed to likely than most other species to stay together locate adequate food supplies, especially in after the young reach independence, and the early spring when insects are inactive and young from early nests are sometimes seen sudden cold spells may cause mortality. feeding siblings at later nests.
Although bluebird sightings during the non- Abundance and Population Trends breeding period are often sporadic and vary with (Click to view trends from the BBS) winter weather and availability of suitable fruit Partners in Flight estimates Eastern Bluebird (Pitts 1979), the species has been more common BBS numbers throughout North America at 8.2 in Michigan winters during recent years as million, roughly 80% of its estimated global shown by CBC data. If winter survival is numbers (PIF 2007). These values far exceed followed by larger numbers of breeding adults, those of its western relatives, the Mountain then recent mild winters might be expected to Bluebird (5.2 million global) and the Western favor increased bluebird populations. As noted Bluebird (1.4 million global) and attest to the in MBBA I and again in MBBA II, the greatest eastern species' adaptability to different habitats. breeding numbers overall occurred in the southern LP, where milder winters and more In states neighboring Michigan, bluebird BBS open woodlands are generally most favorable. data showed an increase of 3.2 percent per year Overall, breeding numbers showed the greatest in New York during 1980-2005 (McGowan and increase from MBBA I to MBBA II in the SLP Corwin 2008), similar to an increase of 2.6 and remained virtually unchanged in the UP. percent per year across its range (Sauer et al. 2008). Wisconsin and Illinois BBS data show Breeding Biology distinct upward trends, with numbers nearly The Eastern Bluebird breeding period begins in doubling in both states from 1980 to 2000. An late March or early April in the southern parts of even larger increase of 5.7% annually was Michigan but is delayed a month or more in the reported for Indiana (Castrale et al. 1998). The north. Weather permitting, multiple broods are mean number of BBS birds reported in Region 3 the norm, especially in the south where given since 1983 (5.12) was nearly double that for pairs may raise two broods (rarely three) per Michigan (2.56); though the difference has season and 8 to 10 or more fledged are not decreased in recent years, both regions show infrequent (Pinkowski 1979). Only a single statistically significant increases (Sauer et al. successful nest is the norm in the UP and 2008). northern LP, but much variation occurs and weather combined with available nesting sites In Michigan, both MBBA I and MBBA II data are important factors influencing annual showed the largest numbers of bluebirds in the productivity. SLP, especially in the southwestern parts of the state, where sandy soils resulting in more open Four or five (rarely six) eggs are laid early in the terrain and milder winters due to the proximity season, and this number is reduced as the season to Lake Michigan are thought to be favorable advances from mid-spring into summer factors. Overall numbers decrease to the north, but again proportional numbers per blocks and
© 2011 Kalamazoo Nature Center Eastern Bluebird (Sialia sialis) Ben Pinkowski townships did not vary much between the two Partners in Flight (PIF). 2007. PIF Landbird atlas projects. Among township blocks, the SLP Population Estimates Database [web region showed a sizeable 12% increase in total application]. Version 2004. Rocky reports from MBBA I to MBBA II (only 1% for Mountain Bird Observatory.
© 2011 Kalamazoo Nature Center