Breeding
Bachman's sparrows' breeding season typically begins in April and continues through August. According to a literature review the earliest date for Bachman's sparrow eggs in Florida is 14 April and the latest date is 4 August. The earliest Bachman's sparrow nest found during a study in longleaf pine habitat of South Carolina was 10 April, while the latest nest found was early in the incubation stage on 5 August. In a study of Bachman's sparrow reproduction in shortleaf and loblolly pine plantations of Arkansas, egg laying started as early as 17 April and continued until 26 August. However, 85% of clutches were started in May, June, or July. A review summarizes the timing of Bachman's sparrow nest construction and egg-laying, including records from more northern areas in the Bachman's sparrow's historic range.
Bachman's sparrows typically raise 2 broods per breeding season and will renest after failed attempts. In shortleaf and loblolly pine plantations of Arkansas, the average time between fledging of the 1st brood and starting the second brood was 12.3 days. This was not significantly (p=0.39) different than the 9.7-day average period between a failed nest and a subsequent nest attempt. On average, females attempted 3.1 nests per season. The maximum number of attempts per season was 5. The maximum number of nests attempted in longleaf pine habitat of South Carolina was also 5. After 2 successful nests, a female attempted 3 times to raise a 3rd brood. Limited evidence, summarized in reviews, suggests that 3 broods per season may occur occasionally. Dates of possible second broods are included in one of these reviews.
Bachman's sparrow nests are constructed on the ground by females and are primarily made of grasses. All nests (n=71) found in a study in shortleaf and loblolly pine plantations of Arkansas were built on the ground. Most nests (70%) were built at the base of bluestem clumps, although nests were found at the base of small trees, forbs, and other grass species. On the same study site, only 7% of nests were not either partially or completely domed. Most nest entrances were oriented to the north. Several reviews summarize information on nest construction.
According to reviews, clutch size varies from 3 to 5. Average clutch size on a site in Arkansas was 3.9, while in a longleaf pine community in South Carolina mean clutch size was 3.6. Both of these studies found significant (p≤0.02) decreases in clutch size as the breeding season progressed. On a dry prairie site in Florida (n=9) average clutch size was 3.44 and on another (n=5) it was 3.6. In shortleaf and loblolly pine plantations of Arkansas, females laid an average of 11.6 eggs (n=20) over the course of the breeding season.
In shortleaf and loblolly pine plantations in Arkansas, females incubated eggs for 13 to 14 days. The average nestling period was 9 days, and the average period between fledging and independence was 25 days. Both parents care for the young during these periods. Although there is a lack of data, a review suggests that Bachman's sparrows probably breed the year after hatching.
Bachman's sparrows exhibit some fidelity to breeding sites. Over a 2 year period in shortleaf and loblolly pine plantations of central Arkansas, 6 of 34 adults returned to areas where they had a territory in a previous year. This varied across years, with a 29% return rate of adult birds banded in 1983 and none of the adults banded in 1984 returning to the site in 1985. No juveniles (n=60) returned to the site.
Read more about this topic: Bachman's Sparrow, Timing of Major Life Events
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