Psychology 351 – Animal Behavior

Alcock, Chapter 2 – Understanding the Proximate & Ultimate Causes of Bird Song
Summary by Kris Mattox
- Almost every bird species is associated with its own distinctive vocalization, an adaptation that helps a male attract a female of the “right” species. Also benefits females by helping them track down males of the “right” species (decreases risk of producing infertile or otherwise disadvantaged hybrid offspring).

Different Songs : Proximate Causes
- How the birds’ genes & environments interact to produce differences among individual males as they are growing up.
  1. Differ genetically in ways that affect the development of the neural mechanisms that control singing behavior, so that birds in two populations eventually come to sing different songs.
  2. Differences in experiences (environmental) that males have early on in life are responsible for their later song differences. Young males learn to sing the dialect of that region by listening to what adult males are singing.

Social Experience & Song Development
- Social Experience : an opportunity to interact with living, breathing companions.
  • In proximate development terms, male birds sing different dialects because young males can be influenced by certain kinds of acoustical and social experiences.

The Development of the Underlying Mechanisms of Singing Behavior
- Birds = Males (2) Z chromosomes, females have Z & W chromosomes (Mammals = Males X & Y, Females (2) X).
- Chromosomes are where the genes are located, and because the avian W chromosome has fewer genes than the Z chromosome, it follows that male and female birds are genetically distinct.
  • Note that the differences between the brains of male and female sparrows are the product of both genetic and environmental differences. A chromosomal (genetic) difference translates into a hormonal (environmental) difference, which leads to differences in the genetic activity of certain cells in the brains of males and females.
- ZENK : an activity of a gene which rapidly increases in certain song control neurons, resulting in corresponding increases in cellular amounts of the protein encoded by that gene.

How the Avian Song Control System Works
- Nuclei : Many anatomically distinct clusters of neurons.
- The various components of the brain are made up of cells (neurons) that communicate with one another via bioelectric messages (action potentials) that travel from one neuron to another via elongate extensions of the neurons (axons).
- HVC : Higher Vocal Center.
- Syrinx : the sound producing structure of birds that is analogous to the larynx in humans.
- Richard Mooney : birds sing two to five song types, each type consisting of a “syllable” of sound that is repeated over and over in a trill that lasts for a couple of seconds.

Different Songs : Ultimate Causes
- When in the distant past did an ancestral bird species start learning its species-specific song, thereby setting in motion the events that led to dialects in birds like the white-crowned sparrow?

The Reproductive Benefits of Song Learning
- A distinctive vocalization conveys information about species membership.
  1. A benefit for males that sang differently from members of other species would be enhanced deterrence of competitors of their own species for territories and mates (males able to more reproductive by defending territories and mates).
  2. Male singers able to communicate their species identity to females might attract mates more readily than those whose songs were less distinctive, and so less recognizable. Females that rapidly locate males of their species can begin reproducing sooner.

The Benefits of Learning a Dialect
  1. The ability of a young male to fine-tune his song so that it resembled the songs of one or more other individuals in a particular region. A young male that learns his song from his elders might then generate calls that travel farther and with less degradation than if he sang another dialect better suited to a different acoustical environment.
  2. The benefits of song learning centers on the advantages of matching songs to the singer’s social environment. The idea is that males able to learn the local version of the species-specific song can communicate better with rivals that will also be singing that particular learned song variant.
  • White-Crowned sparrows typically sing (1) song type, with different populations having their own dialects.
- Michael Beecher : Type Matching – a male hears a neighbor’s song coming from a neighbor’s territory, and he will sing a song from his own repertoire that matched one in the repertoire of that particular neighborhood.
- Repertoire Matching – a bird exposed to the song type from a neighbor responds not with the exact same type, but with a song type drawn from their shared repertoire.

Female Preferences and Song Learning
- By learning to sing the dialect associated with their place of birth, males could announce their possession of traits (and underlying genes) well adapted for that particular area and females would be attracted to them.
- Females also look to the learned details of a potential mate’s song for information about developmental history. If a female could tell just by listening to a male that he was unusually healthy, she could acquire a mate whose genes had worked well during his development and so should be worth passing on to her offspring.

Proximate and Ultimate Causes are Complementary
- Proximate Causes : Differences in gene – environment interactions, hormonal differences, differences in song system construction, and differences in song system operation.
- Ultimate Causes : Song differences among individuals, differences in reproductive success = natural selection, genes transmitted to the next generation, differences in gene – environment interactions in individuals, process repeats itself.