Oxygen stores and foraging behavior of two sympatric, planktivorous alcids

Abstract

Seabird species with overlapping diets commonly coexist at breeding colonies. For example, ancient murrelets Synthliboramphus antiquus and Cassin's auklets Ptychoramphus aleuticus are similar-sized small alcids that feed on krill and small fish. Little is known regarding their partitioning of aquatic resources, so we assessed the O 2 stores and foraging behavior of sympatrically breeding populations of these species. The attachment of recorders (1 to 3% of body mass) caused substantial nest desertion, but we reduced these effects by only equipping experienced birds early in the day. Auklets and murrelets had 18 to 24% higher mass-specific O 2 stores than slightly larger nondiving kittiwakes Rissa tridactyla. When compared to published values, blood hemoglobin content was higher, muscle pH buffering capacity was similar and muscle myoglobin content was lower for small divers than for larger non-phocid divers. The slightly higher O 2 stores of Cassin's auklets was reflected in their aquatic behavior, as auklets dived longer than murrelets at any given dive depth. Moreover, chick-rearing auklets spent 31% more time underwater than incubating auklets and 50% more time underwater than incubating murrelets. In total, 45% of dives by chick-rearing auklets, 36% of dives by incubating auklets and 13% of dives by incubating murrelets exceeded their estimated aerobic dive limits. Murrelets primarily used V-shaped dives while auklets generally exhibited W-shaped dive profiles with a protracted bottom phase. Thus the O 2 stores and foraging behavior of the 2 sympatric seabirds differed.

High flight costs, but low dive costs, in auks support the biomechanical hypothesis for flightlessness in penguins

“…Larger body size increases dive duration and efficiency (14,15). Thus, loss of flight in diving birds appears to be followed by the rapid evolution of large body size, as shown by the presence of early giant penguins (20).…”

“…), and foot-propelled diving seabirds-the only other animals to routinely occupy all three media as adults-wing design in auks and other wingpropelled diving seabirds functions for both underwater and aerial locomotion (10-13). Extant flightless seabirds (penguins) evolved enhancements for underwater locomotion by reducing wingspan, enlarging wing bones, increasing body mass, optimizing muscle contraction rate for low-wingbeat frequencies, and augmenting myoglobin stores to increase dive endurance (1,14,15). In contrast, birds that both fly and dive, such as auks, are restricted by aerial flight demands for opposing adaptations (1,12,14).…”

“…Extant flightless seabirds (penguins) evolved enhancements for underwater locomotion by reducing wingspan, enlarging wing bones, increasing body mass, optimizing muscle contraction rate for low-wingbeat frequencies, and augmenting myoglobin stores to increase dive endurance (1,14,15). In contrast, birds that both fly and dive, such as auks, are restricted by aerial flight demands for opposing adaptations (1,12,14).We tested the biomechanical hypothesis for the evolution of flightlessness in seabirds by measuring the energy costs of flight and diving in two species of free-living, diving seabirds that are also able to fly: wing-propelled thick-billed murres (Uria lomvia) and foot-propelled pelagic cormorants (Phalacrocorax pelagicus). We predicted that murres would have elevated flight costs compared with nondiving birds, but would have low costs of swimming, although not as low as penguins, which have lost the ability to fly.…”

Counting calories in cormorants: dynamic body acceleration predicts daily energy expenditure measured in pelagic cormorants

“…large body, high myoglobin concentration in muscle) and what is optimal for flight (e.g. small body, low myoglobin concentration in muscle to provide more space for mitochondria to power flight; Croll et al, 1992;Elliott et al, 2010). Apart from morphological constraints, flight costs in cormorants may also be high because they have wettable plumage.…”

Working beneath the surface: interplay of biomechanics, physiology and behavioural ecology in diving seabirds

“…The second, by Lovvorn et al (2010), notes that although the size of the smallest marine endotherms, the auklets, currently makes them unsuitable for an animal-attached device approach, judicious modelling can help make predictions about the way these animals must operate in their cold, marine environment. Small, planktivorous alcids are also the subject of the work by Elliott et al (2010), which examines how oxygen storage capacity relates to foraging behaviour in two sympatric species, while, in stark contrast, Ponganis et al (2010) focus on how oxygen store depletion and the aerobic dive limit relate to dive performance in the world's largest diving seabird, the emperor penguin Aptenodytes forsterii. Dive performance is also affected by stroke frequency in diving seabirds and in the fifth paper, Mori et al (2010) consider optimization of this in South Georgian shags Phalacrocorax georgianus.…”