Bird I: Song
Learning, Migration, and Sexual Selection case study – Kristen Weiss Sanders
·
Why do we study
song learning in birds?
o
underlying neural,
genetic, developmental, and hormonal mechanisms
o
model for studying
“language”
·
Visualizing sounds
made by animals:
o
Oscillograms (pg.
27, Fig. A)
§
amplitude = height
of wave = volume
·
é
amplitude =
é
volume
§
frequency = # of
waves in a time period = pitch
·
é
frequency =
é
pitch
o
Spectrograms/Sonograms (pg 27, Fig. B)
§
frequency changes
over time
§
syllables (ex:
whistle, buzz, trill)
·
Intraspecies
dialects: three hypotheses (Hypotheses 2.1, pg. 29)
o
genetic differences
hypothesis (pgs. 28-31)
o
acoustic stimulus
hypothesis (pgs. 31-32)
o
social interaction
hypothesis (pgs. 33-34)
o
**be able to give
an example of data (real or hypothetical) that supports EACH**
·
Evolution of song
learning (pgs. 40-43)
o
occurs in 3 of 23
avian orders: parrots, hummingbirds, “songbirds” (oscines)
o
other 20 have
complex vocalizations, but learning not involved
·
The adaptive value
song learning
o
nutritional stress
hypothesis (pgs. 45-46)
§
brain structures
underlying song learning (and production) develop early in life when young birds
are under a lot of developmental/nutrition stress
§
why is this worth
it?
o
environmental
stress hypothesis (pg. 46)
§
vocal learning =
acoustic adaptation of vocal signals to the local habitat
§
ex: lower
frequencies in dense forests
o
recognition
hypothesis (pgs. 46-49)
§
vocal learning =
more vocal signals becoming more recognizable
§
promotes social
cohesion in a group
§
ex: is that other
bird a competitor? an ally? related to you?
o
information-sharing
hypothesis (pgs. 49-50)
§
vocal learning =
expansion of vocal repertoire in systems where living with kin favors more
information sharing
§
ex: sending out an
alarm or establishing contact in a group
o
sexual selection
hypothesis (pgs. 50-51)
§
vocal learning =
increased complexity of the vocal repertoire
§
ex: male-male
competition or female preference
o
geographic matching
hypothesis (pgs. 52-55)
§
vocal learning
evolves to promote geographic variation in signals
§
allows assortative
mating and promotes local adaptation
§
ex: female chooses
a mate NOT from her natal area
à
increases the genetic diversity of her offspring
Territoriality and
Migration
– James K. Adams
·
Territories
typically protect “best” habitat in relation to some resource; since this
requires expenditure of energy, it makes sense only to do so if it improves
fitness (reproductive success) – a cost-benefit analysis
·
Interestingly,
defending the “ideal” habitat doesn’t always increase fitness
o
Blackcap warbler
example (pgs. 220-221) – density-dependent habitat selection
o
Red-winged
blackbird female example (pg. 221) – lower quality habitats may be chosen for
various reasons; this allows for predictions of distribution of individuals,
both male and female, which may have different fitness outcomes
·
Better competitors
should therefore occupy the highest quality habitat
o
American redstarts
occupying favorite overwintering habitat in Jamaica (pgs. 226-228) get the
following benefits:
§
They can leave
overwintering sites earlier to get a head start on getting spring territories to
improve getting resources and attracting mates
§
More resources in
wintering grounds so that when they return to summer grounds they have resources
stored for more reproductive success
·
Territorial combat
usually brief – remember reptiles
o
Size/Fat reserve
effects (pgs. 232-233)
o
Age effects (pg.
233-234)
o
Resident advantages
(red-shouldered widowbirds, pg. 232)
·
Dispersal (pg. 237)
– inbreeding avoidance, as suggested above under geographic matching hypothesis
·
Migration
o
Examples of long
distance migration (see Powerpoint and pg. 240)
o
Tropical origins
hypothesis – moved to temperate areas to make use of abundant resources during
favorable times during the year (pg. 241)
o
Temperate origins
hypothesis – moved to tropics to move away from unfavorable conditions (pg. 241)
·
Costs and benefits
o
Costs (pgs.
243-246)
§
energy expenditure
– fly at times and altitudes that minimize losses
§
risk of dying
(predation, low reserves); explains why many birds migrate at night
o
Benefits (pgs.
247-250)
§
massive numbers of
insects that become available in temperate and even subarctic habitats with long
daylight hours for insect growth and bird feeding.
These are bottom-up forces.
§
Top-down forces,
such as temperature (monarch butterfly).
·
Cues – photoperiod,
weather/temperature
·
Migration
mechanisms – landmarks (rivers, coastlines, highways), sun/star compasses,
geomagnetism
Sexually Selected
Post-Mating Behavior
-- Bloo Mitchell
I.
Color in Birds
a.
Color matters in
the avian world!
b.
Secondary sexual
characteristics
c.
Female selection of
bright colored males has been extensively studied
d.
More recently,
scientists have been looking at female signals to attract better mates
II.
Egg Coloration
a.
Eggs were not
always so widely variable, but now the differences are immense! Both
interspecific and intraspecific.
b.
Large diversity
created by a combination of two pigments: biliverdin and protoporphyrin
i.
Protoporphyrin –
red/brown variations
ii.
Biliverdin –
blue/green variations
c.
But why evolve this
range and diversity of colors?
III.
Egg Coloration
Hypotheses
a.
Crypsis for defense
against predators
b.
Protection against
brood parasitism
c.
Structural
integrity
d.
Thermoregulation
e.
Sexually Selected
Egg Color Hypothesis (SSECH)
i.
Egg color may
function as a post-mating sexually selected signal of the female’s genetic
quality to their mates to induce higher parental care
IV.
SSECH Assumptions
a.
Biliverdin is
limited and costly. Females allocating it to their eggs may be able to signal
their ability to cope with less and thereby being superior to other females.
b.
Healthier females
can allocate more biliverdin to their eggs and lay deeper blue. This is an
honest signal of their physical condition.
c.
Males adjust their
feeding rates based on egg color and ultimately increase their biological
fitness.
d.
Higher feeding
rates and healthier females should lead to better quality chicks.
V.
Study Methods
a.
Egg coloration was
measured with a spectrometer. Only the high and low quartiles were used in the
study.
b.
Pale eggs were
swapped with dark eggs, and dark eggs were swapped with pale eggs.
i.
For the control,
pale eggs were swapped with unrelated pale eggs and dark eggs were swapped with
unrelated dark eggs.
c.
Not all the chicks
were placed back into their original nests.
d.
Visitation was
measured for eight hours on the 4th and 12th days.
VI.
Study Conclusion
a.
Males do not adjust
their visits based on egg color.