The singing phenology of Bachman's sparrow: implications for monitoring programs

Abstract Singing in passerine birds is a fundamental reproductive behavior and is an important cue for detections in avian surveys, but variation in abiotic conditions (e.g., temperature, photoperiod) can influence singing phenology and daily singing behavior, impacting survey efficacy. The effectiveness of monitoring efforts is particularly essential for species of conservation concern, as the resulting data often guide management decisions. Bachman's sparrow ( Peucaea aestivalis ) is a passerine of conservation concern in open woodland savannas in the southeastern USA, and while surveys for the species typically occur in late spring and early summer, a broader survey window may be possible for efforts aiming to detect it earlier or later in the year (e.g., during territory establishment or the fledgling stage). Empirical studies investigating Bachman's sparrow singing phenology or the abiotic influences of its daily singing behavior are lacking, and such insight can improve the effectiveness of monitoring efforts. We deployed automated recording units to determine the annual singing period of Bachman's sparrow at 6 sites of known occupancy in Texas, USA, surveying daily from 8 February 2020 to 3 March 2022. We performed logistic regression analyses to investigate the relationship between the occurrence of singing and daily temperature (°C), precipitation (mm), wind speed (m/s), and photoperiod (photoperiod T ) during the singing season. Across the 3 years surveyed, Bachman's sparrow sang as early as 19 January and as late as 6 October, with the greatest proportion of surveys with detections occurring between March and August. Our top model indicated that odds of singing increased with increasing photoperiod until mid‐to‐late April, and temperature most strongly affected odds of singing early (February and March) and late (July and August) in the singing season. Our results agree that Bachman's sparrow surveys are most effective between March and August, while efforts to detect the species early or late in the season can begin as early as January and end as late as September.