Paper topics

Chapter 2: Using bird singing behavior as a case study of how to apply the scientific method to produce and answer questions of proximate and ultimate causation.

Bird song facts:1. There are about 4000 species of song birds each of which usually

produce 1 to many bird songs. 2. In all studied cases adult song has been shaped by learning. 3. In most cases it is the male of the species that produces song,

whereas females typically produce very little or no sound/song. 4. Males within any single species tend to sing highly similar sets of

songs but may also have dialectic variations for a given song. These dialects are observable when comparing songs across different geographic regions. • In some cases, dialectic variations of a song within a region will

change over time (i.e. across generations).

Questions about proximate cause of bird song variation:1. How do within species dialects develop what are the characteristic

differences in song pattern? 2. Are there regional preferences among females for local dialects? 3. What are the developmental differences between males and females that

produces male singers? 4. What are the brain structures involved in song production and how do they

develop? 5. What genes/proteins/hormones are involved in song production?

Questions about Ultimate cause of bird song variation:1. Why do birds appear to have to learn the details of their songs as juveniles? 2. Hwy are males usually the singer.3. Why do dialects exist in nature?

1. Do dialects provide an adaptive advantage? 2. Are they a product of local genetic differences? 3. Are they the results of an accidental mispronunciation that is learned?

Proximate Cause Case Study: The White Crowned Sparrow

Song learning: Modern experimental studies of song learning in birds began in the 1950's in laboratory of W.H. Thorpe.  Birds that were hand-reared from an early age without hearing the normal adult song of its species, a simplified "isolate" song is produced.

Isolate songs are highly variable within a species but tend to be related in some rudimentary way with a normal song.

A song developed by a male white-crowned sparrow that was tutored early in the first 2 months of life.

Here is the tape-recorded song he was tutored with. 

Song learning facts: 1. Juveniles need adult “tutoring” to

produce normal song. 2. There is variability across

individual songs: this may be the basis of dialect formation.

3. Juveniles prefer/learn songs of their species better than they learn other species songs.

Gene environment interactions: Within species preferences for song learning

Baptistia and Petrinovich

Experiment1: within vs between species tutoring

Given a choice there is an innate preference for ones own species song•True even at the subspecies level.

Within species preferences for song learning

Experiments 2: between species ONLY tutor

Conclusion: White Crowns will learn a song; if their own species is not present they will learn what is abailable

Baptistia and Petrinovich

Stages of song development

Normal song development proceeds through a series of stages:  1. Young male memorize songs of one or more adult birds. 

• Sensitive phase (~10-50 days post hatch) a developmental window where babies listen and learn. 

2. Vocal production begins during or soon after the sensitive phase when the male begins subsong. 

• Subsong has been compared to babbling in human infants.  • Birds that do not learn to sing do not produce subsong.  

Example: subsong “babbling” performed by a 240 day old white-crowned sparrow.

3. Subsong gives way to plastic song: organized imitation songs • The first evidence of imitations of tutor songs appears in the male's singing.

 • Plastic song, imitations are often incomplete.  • Developed songs tend to be "hybrid" songs composed of parts of two or

more different tutor songs.  • Overproducing: singing more imitations than eventually appear the final

crystallized song. • Crystallized songs can change over time.

Stages of song development

Example: Plastic songs by a 260 day old sparrow containing three different songs.  The three tutors that the male memorized during the sensitive phase are shown above, and are connected by arrows to the young male's imitations. 

Stages of song development

4. Crystallized song: The emergence of the adult song occurs through the process of selective attrition of syllables from overproduced plastic song repertoire• Mediated by hearing the song of the tutor and auditory feedback. 

Example: The first song is the tutor, the second is the juveniles rendition of the matching song type.   This male has stopped singing his imitations of Tutors 2 & 3, (above) and will retain his crystallized imitation of Tutor 1. 

Stages of song development

**Selective attrition may lead to vocal dialects, in which neighboring males sing very similar songs that differ from the songs at other locations.

Proximate cause of Dialectic differences?

1. Environment 2. Error and learning “culture”3. Genetic drift with natural selection