Skill rather than beak kinematics affects seed handling performance in a granivorous songbird

Abstract

In granivorous songbirds, feeding is a complex process as seeds need to be dehusked before they can be consumed, making the feeding act a biomechanically challenging endeavour. However, most previous research has focused on how beak morphology affects feeding performance, while the influences of beak kinematics remain largely unknown. In this study, we hence investigated at the individual level how feeding performance (i.e. seed processing time and success rate) relates to both beak kinematics (i.e. beak tip speed, acceleration, frequency) and skill (i.e. seed handling tactics and cracking techniques) in the Canary Serinus canaria. To do so, high‐speed videos during feeding were recorded and subjected to automated tracking of beak tip movements. Better skills, that is accurate positioning of the seed for being split in half, reduced total seed handling time compared to more random positioning and crushing the husk into multiple, scattering fragments. Surprisingly, individual variation in beak speed, acceleration or frequency generally did not relate to differences in performance. Thus, our data suggest that seed positioning precision, and hence the control of coordinated beak and tongue movement, is critical to minimize feeding durations in songbirds. Further studies are needed to explore whether this develops via a positive feedback between behaviour, learning and increased efficiency or if it relates to intrinsic differences. Read the free Plain Language Summary for this article on the Journal blog.

Seed preference is only weakly linked to seed-type-specific feeding performance in a songbird

“…The degree of seed specialization, represented by Levin's niche breadth index, only had a significant effect on beak frequency in its interaction with the two experimental seed types (Levin*seed_type, P =0.032). Specifically, more generalist individuals opened and closed their beaks more slowly (during the act of seed positioning, see Andries et al, 2023a , b ) than more specialist individuals, but only during feeding on hemp seeds ( Fig. 3F ).…”

“…Data points represent individual birds. Handling skill is represented by the proportion of seed husks that are being split in half as opposed to being crushed indiscriminately ( Andries et al, 2023a , b ). Significant relationships ( P <0.05) of the linear mixed models are represented by a regression line and its 95% confidence interval shaded in grey.…”

“…Hemp seeds are high in calories ( Table 1 ) and typically preferred food items in canaries ( Kear, 1962 ). However, hemp seeds are relatively large and are therefore difficult and time-consuming to dehusk ( Andries et al, 2023a , b ). Thus, there could be a trade-off between energetic content and feeding effort, where individuals that prioritize feeding on fewer, but more nutritious seeds show a stronger preference for hemp seeds.…”

“…As a general example, juvenile birds display worse seed handling skills due to inexperience and are hence slower and less successful at feeding on more difficult-to-process seeds than adults, which causes juveniles to prefer easier-to-process seed types ( Kear, 1962 ; Wunderle, 1991 ). However, seed handling times, husking success rates and seed-handling skills have been observed to vary significantly even among adult individuals ( Andries et al, 2023a , b ), so individual variation in seed preferences might be significant regardless of age.…”

“…As mentioned earlier, individuals can select seeds based on handling efficiency and appropriate handling skills ( Kear, 1962 ; Titulaer et al, 2018 ). Better handling skills improve seed-handling time ( Andries et al, 2023a , b ) and skills are expected to improve with experience (e.g. Briffa and Lane, 2017 ).…”