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.

Variation in offspring development is driven more by weather and maternal condition than predation risk

“…Capture attempts were a maximum of 45 min (average = 17.5 ± 1.3 min) per day (max =2 days). We observed no cases of premature fledging, and capture events likely did not prolong the nestling period because released larks return to normal provisioning behaviour within 15 min (de Zwaan, Trefry, & Martin, 2018). Each female lark was banded with one U.S. Geological Survey numbered aluminium band and three plastic colour bands for subsequent identification.…”

Sex-Specific Spatiotemporal Variation and Carry-Over Effects in a Migratory Alpine Songbird

“…Nests were monitored every 2 days to record nest fate (fledged, depredated), clutch size, and number of fledglings. Both males and females were captured at the nest during the nestling period using bownets that were triggered when adults entered to provision the nestlings (de Zwaan et al, 2018). Each adult was measured for body size and condition traits (i.e., wing, tarsus, mass, fat) and ringed with one U.S. Geological Survey numbered aluminum ring and three color rings for subsequent identification.…”

“…We monitored individuals for ∼15 min after release to ensure there were no immediate effects of the geolocator. The following year, returning individuals with geolocators were captured at the nest during the nestling stage (males) or the incubation stage (females) using a noose-line trap surrounding the nest (de Zwaan et al, 2018). We removed the geolocator from recaptured birds, measured body size traits, and released them in under 5 min.…”

Noose Carpets: A Novel Method to Capture Rails

“…Leg‐hold traps (including noose carpets) are commonly used to capture raptors (Bloom 1987), shorebirds (Mehl et al 2003), Galliformes (Ramesh and Kalsi 2007), and occasionally songbirds (de Zwaan et al 2018), but they had not been used effectively to capture rails before this study. Zembal and Massey (1983) attempted to use noose carpets to capture light‐footed Ridgway's rails in California but abandoned their attempts when they observed rails walking over the nooses without getting caught.…”