Filter-feeding dabbling ducks (Anas spp.) can actively select particles by size.

Area of Science:

• Ornithology
• Animal Behavior
• Functional Morphology

Background:

• Filter-feeding dabbling ducks (Anas spp.) exhibit poorly understood relationships between bill structure, feeding function, and prey selection.
• Interspecific variation in duck bill morphology may influence prey retention and resource partitioning, but the exact mechanisms are unclear.

Purpose of the Study:

• To investigate whether interspecific differences in duck bill morphology affect prey retention, enabling resource partitioning.
• To test the hypotheses that prey retention is solely determined by interlamellar distance or if lamellar separation plays a role in selective particle expulsion.

Main Methods:

• Experimental feeding trials with three dabbling duck species using mixed seed types (millet, wheat, poppy) of varying sizes.
• Analysis of seed ingestion proportions compared to unmixed foraging rates to infer selective feeding behaviors.

Main Results:

• Ducks ingested a higher proportion of preferred large seeds (millet, wheat) over smaller, less preferred seeds (poppy), even when all exceeded interlamellar distance.
• Ingestion proportions differed significantly from expected rates based on unmixed prey, indicating active avoidance of poppy seeds.
• Results support the lamellar separation hypothesis and refute the sole role of interlamellar distance in prey retention.

Conclusions:

• Dabbling ducks actively select prey size using lamellar separation, not solely relying on fixed interlamellar distance.
• Lamellar separation allows for selective expulsion of unwanted particles, facilitating prey partitioning.
• A potential trade-off exists between particle size selection (via lamellar separation) and ingestion rate, influencing interspecific resource partitioning.