Blue Grosbeak

Guiraca caerulea

Blue Grosbeaks typically associate with shrubby thickets interspersed with grassy fields, fence rows, roadsides and forest edges. Nests are usually low in small trees, shrubs, or tangles of vines, briars, and other vegetation and often near open areas or roads (Ingold 1993). Although Blue Grosbeaks are generally scarce (Ingold 1993), evidence suggests they are increasing in Missouri. The Missouri Breeding Bird Survey indicated a 1.2 percent average annual increase from 1967 through 1989 (Wilson 1990).

Code Frequency

Blue Grosbeaks are easy to locate wherever they occur because they tend to select open perches and their vocalizations are easily detected. Therefore, where Blue Grosbeaks were not recorded, they likely were not present. Because Blue Grosbeaks nest in brambles and other difficult-to-reach habitats, their nests and other confirming breeding evidence are difficult to observe. Therefore, it is likely that many probable breeding blocks contained nest sites. Most breeding was confirmed by the observation of fledglings or food for young. Of the 694 blocks where Blue Grosbeaks were found, nests with Eggs: or young were observed in only three.

Distribution

Blue Grosbeaks were widely distributed in southern Missouri, occurring in nearly 100 percent of the blocks near Missouri's southern border, except in the Mississippi Lowlands, where they are rare. In contrast, they were nearly 100 percent absent near the northern border of Missouri, which is near the northern edge of the Blue Grosbeak's breeding range.

Average Number of Birds / 100 stops

Abundance

Blue Grosbeaks were most abundant in south central Missouri and portions of the southwestern corner of the state, which is the center of their southern Missouri range. These regions contain the mix of grasslands, brush and trees characteristic of Blue Grosbeak habitat.

Phenology

An accurate picture of the Blue Grosbeak's nesting phenology is afforded by 122 blocks in which breeding was confirmed. Second broods are common in the southern part of the breeding range (Ingold 1993), which may account for the late observations of nest building and a nest with young. In Oklahoma, Sutton (1967) found a nest with Eggs: on August 6 and recently fledged young on August 28.

Notes

Of the 45 blocks where Atlasers observed nest contents or fledglings, four instances of Brown-headed Cowbird parasitism were recorded. Ingold (1993) describes Blue Grosbeaks as a heavily-parasitized species.

Breeding Evidence

Reported in 694 (57.5%) of 1,207 blocks

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