Title

Effects of Transmissivity on Aerodynamic Function in Bird Feathers

Presentation Type

Poster

Abstract

We studied the relationship between flight performance and the transmissivity of feathers in birds to provide insight into the evolutionary significance of feather structure. Several aspects of bird feathers change during development and are correlated with improved aerodynamic performance. As birds age, their wings fill in (macro-scale transmissivity decreases), flow decreases across the barbules of individual feather (microscale transmissivity decreases), and feathers get stiffer. Our present experiments allow us to test the effects of microscale transmissivity in isolation from the other two variables. We examined primary feathers from four peacocks (Pavo cristatus). This species was used due to size convenience of their feathers. First we measured force production by the untouched, intact feathers in a wind tunnel set to a constant 7 meters per second air speed. Airflow through the barbules (transmissivity) was measured using a pressure gauge and suction pump. The feathers then underwent different manipulations to change transmissivity and the processes were repeated once for each feather; we decreased transmissivity by applying Tresemè Mega-Firm Hairspray and then increased transmissivity by brushing the feathers with a toothbrush. The results were displayed in a parabolic graph that plotted lift against drag, a common device used to understand transmissivity. Lift:drag ratio (aerodynamic efficiency) increased with hairspray application and decreased with brushing. Our results thus provide new insight into the functional signficances of transmissivity, and reveal that other evolutionary pressures besides minimizing transmissivity have shaped feather morphology in birds. Alternative pressures might include phylogenetic inertia, or a compromise with the need to avoid breakage.

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Apr 12th, 11:00 AM Apr 12th, 12:00 PM

Effects of Transmissivity on Aerodynamic Function in Bird Feathers

UC Ballroom

We studied the relationship between flight performance and the transmissivity of feathers in birds to provide insight into the evolutionary significance of feather structure. Several aspects of bird feathers change during development and are correlated with improved aerodynamic performance. As birds age, their wings fill in (macro-scale transmissivity decreases), flow decreases across the barbules of individual feather (microscale transmissivity decreases), and feathers get stiffer. Our present experiments allow us to test the effects of microscale transmissivity in isolation from the other two variables. We examined primary feathers from four peacocks (Pavo cristatus). This species was used due to size convenience of their feathers. First we measured force production by the untouched, intact feathers in a wind tunnel set to a constant 7 meters per second air speed. Airflow through the barbules (transmissivity) was measured using a pressure gauge and suction pump. The feathers then underwent different manipulations to change transmissivity and the processes were repeated once for each feather; we decreased transmissivity by applying Tresemè Mega-Firm Hairspray and then increased transmissivity by brushing the feathers with a toothbrush. The results were displayed in a parabolic graph that plotted lift against drag, a common device used to understand transmissivity. Lift:drag ratio (aerodynamic efficiency) increased with hairspray application and decreased with brushing. Our results thus provide new insight into the functional signficances of transmissivity, and reveal that other evolutionary pressures besides minimizing transmissivity have shaped feather morphology in birds. Alternative pressures might include phylogenetic inertia, or a compromise with the need to avoid breakage.