Efficiency and fitness consequences of two trapping methods for recapturing ground-nesting songbirds

Abstract

Capturing nesting songbirds is a core component of many field studies. However, avoidance of traps and mist-nets by birds can reduce capture efficiency and bias study results, particularly when individuals need to be recaptured multiple times. We describe a novel capture method—the noose-line—for an alpine population of Horned Larks (Eremophila alpestris) studied during three breeding seasons (2015–2017) in northern British Columbia, Canada. Our objective was to develop a safe, efficient method to recapture individuals that exhibited trap avoidance. We compared the capture efficiency (trap success relative to capture effort) and fitness consequences (nest survival and nest attentiveness) of the noose-line (non-selective method) to those of a more traditional bownet trap (selective method) for both naïve (not previously captured) and previously captured Horned Larks. Mean trapping success for the noose-line was high for both naïve (89.7%) and previously captured (62.9%) birds, whereas mean trapping success for the more visible bownet was strongly influenced by bird experience (naïve = 41.4%, previously captured = 12.1%). However, mean capture effort (time required for successful capture) was greater for noose-lines than the bownet (45.3 min vs. 17.5 min) and noose-lines were more likely to capture non-targeted individuals. The trap type used to capture birds did not influence nest survival. Overall, our results suggest that noose-lines can be an effective option for capturing ground-nesting songbirds, particularly for studies where birds must be recaptured, e.g., to retrieve tracking devices or repeatedly measure body condition.