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) -- familiarity with territory and payoff asymmetry hypothesis

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.

b.  Because not all chicks were swapped back to their original nest, it opened another variable of interest. Males were likely to visit their nest more often if their original chicks were returned. This begs the question: Can male Easten Bluebirds recognize their own offspring? This is called “self-referent phenotype matching” and is the ability of one individual to recognize self in its kin