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for individual survival in order to get to the next reproductive season. One
example is migration. Migration refers to general animal movement, and is
widely found in Kingdom Animalia, from mammals to arthropods
( Dingle & Drake, 2007; Drickamer, Vessey, & Jakob, 2002 ). Seasonal
migration is an adaptive behavior where animals relocate prior to the onset
of unfavorable conditions, such as cold temperatures and low food availabil-
ity. In this section, we will focus on bird migration, one of the most well-
known and well-studied examples. The arctic tern ( Sterna paradisaea ) is the
most extreme case, with some individuals annually flying over 80,000 km
roundtrip between the Arctic and the Antarctic ( Egevang et al., 2010 ).
Migration consists of two phases, a preparation phase and the actual migra-
tion phase. Both phases are seasonally timed according to photoperiod, a con-
sistent and reliable seasonal cue ( Drickamer et al., 2002 ). In the preparation
phase, there are substantial behavioral, morphological, and physiological
changes that occur, including hyperphagia ( Odum, 1960 ), accumulation of
fat reserves ( Ramenofsky, Savard, &Greenwood, 1999 ), muscle hypertrophy
( Piersma, 1998 ), and changes in energy metabolism that specifically increase
capacity for fatty acid utilization ( Guglielmo, Haunerland, Hochachka, &
Williams, 2002; Guglielmo, Williams, Zwingelstein, Brichon, & Weber,
2002 ). Prior to migration, birds exhibit increased activity levels at the time
of day they would normally migrate, termed migratory restlessness, which
occurs even in captive birds kept
in constant conditions ( Drickamer
et al., 2002 ).
During the migration phase, there is considerable species-specific varia-
tion, particularly in trip length, direction of travel, final destination, and fre-
quency/duration of stopovers for feeding. Stopovers serve an important
purpose in allowing the bird to replenish energy reserves lost during flight,
and the frequency and duration of these stopovers has a great effect on total
migration time ( Schaub, Jenni, & Bairlein, 2008 ). Selection of stopover sites
is important, because stopping at ideal areas with greater food availability can
decrease the overall amount of time spent at the site. However, other factors
can affect site selection as well, including the migrant's energetic condition,
wind, and weather conditions ( Moore, Woodrey, Buler, Woltmann, &
Simons, 2005 ). Some species fly over large bodies of water making it impos-
sible to stop until reaching the other side ( Larkin, Griffin, Torre-Bueno, &
Teal, 1979; Lowery, 1946 ). Therefore, stopovers must be precisely timed
and coordinated to maximize fitness, both to accumulate enough energy
for flight and to arrive at the final destination at the appropriate time.
In spite of the wealth of information available about migration physiology,
there is little known about how migration is seasonally controlled at the
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