Alcids 'fly' at efficient Strouhal numbers in both air and water but vary stroke velocity and angle.
Birds that use their wings for 'flight' in both air and water are expected to fly poorly in each fluid relative to single-fluid specialists; that is, these jacks-of-all-trades should be the masters of none. Alcids exhibit exceptional dive performance while retaining aerial flight. We hypothesized that alcids maintain efficient Strouhal numbers and stroke velocities across air and water, allowing them to mitigate the costs of their 'fluid generalism'. We show that alcids cruise at Strouhal numbers between 0.10 and 0.40 - on par with single-fluid specialists - in both air and water but flap their wings ~ 50% slower in water. Thus, these species either contract their muscles at inefficient velocities or maintain a two-geared muscle system, highlighting a clear cost to using the same morphology for locomotion in two fluids. Additionally, alcids varied stroke-plane angle between air and water and chord angle during aquatic flight, expanding their performance envelope.
['Lapsansky|Anthony B|AB|0000-0001-7530-7830', 'Zatz|Daniel|D|', 'Tobalske|Bret W|BW|']
D000818:Animals D001696:Biomechanical Phenomena D046091:Charadriiformes D005426:Flight, Animal D013550:Swimming D014921:Wings, Animal
strouhal number wing flight locomotion ecology evolutionary biology muscle efficiency swimming