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cies preferred to use some maneuvers more
than others and tended to be particularly
good at their favored maneuvers.
Larger hummingbird species have disproportionately large muscle capacity
and wing size, which generally resulted in
higher maneuverability. However, other
traits accounted for variation among species in the ability to perform some maneuvers. For example, the use of rotational
maneuvers was largely determined by the
surface area of the wings and by the muscle
capacity. Forward acceleration, velocity, and
deceleration were accounted for mostly by
muscle capacity. Wing shape was only a major factor in determining variation in some
aspects of turning performance. In combination, slight changes in body size, flight
muscle capacity, wing size, and wing shape
account for much of the variation in flight
tendencies and the performance of different
maneuvers among hummingbirds.
Given that the birds in this study were not
being challenged to perform maneuvers at
the limits of their abilities, it is remarkable
that a handful of underlying traits accounted
for 25 to 40% of the evolution in most performance metrics. This could indicate that
hummingbirds operate near their limits even
when not severely challenged, or that even
flying around enclosures in relaxed conditions they show tendencies and abilities that
parallel their maximum flight capacity.
Given the importance of flight to the hum-
mingbird lifestyle, one could easily imagine
that flight performance has diversified in
response to different ecological conditions
encountered by species. However, the spe-
cies included in Dakin et al.’s study showed
very strong phylogenetic conservation of
flight behavior and performance. This find-
ing suggests that ecological diversity in the
major hummingbird lineages must have
another functional basis. Future studies
should aim to identify the role of flight abil-
ity evolution in hummingbird diversifica-
tion. With more than 330 species, there is
much ecological diversity to account for (8).
Researchers are now in a strong position
to determine the adaptive importance of
diversity in the use of maneuvering behaviors among hummingbird species. One may
wonder why there is diversity in flight performance at all. Typically, diversity in a major
functional system arises because of trade-offs associated with underlying traits. These
trade-offs may or may not also relate directly
to flight performance. For example, body size,
the most potent driver of maneuvering performance in the present study, has numerous
impacts on hummingbird biology, including
their energy needs, reproductive success,
and performance in long-distance migration.
Thus, the body mass of a species reflects the
interaction of many factors, including flight
performance. Differences among species
in the consequences of body size will lead
to differences in flight performance. Other
important flight traits may have fewer ad-
ditional implications for fitness, such as the
shape of the wing. Thus, wing shapes may
more closely track the aspects of flight perfor-
mance that are most important to the ecol-
ogy of the species.
Dakin et al. provide a blueprint for how to
begin to understand the relative importance
of different maneuvers to different hummingbird species. Getting from observations of the
sort they made to characterizing locomotion
in wild birds will require the development of
tiny data loggers that can be affixed to these
tiny birds but do not interfere with flight.
With such devices, researchers would be
able to determine the flight tendencies and
performance of birds in the course of their
everyday life. Dakin et al. have deepened
our understanding of how traits shape flight
performance, setting the stage for others to
explain how diversity in maneuverability and
other aspects of flight performance relate to
species ecology (9–11). j
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Photographs of Inagua woodstar hummingbirds
(Calliphlox lyrura) show their complex flight maneuvers.