Integrative Study of Bird Song – Key Vocabulary

Comparative Approach: Gull Nesting Behavior

• Observation of extant species

  • Most gull species: ground‐nesting, colonial.

  • Kittiwake: cliff‐nesting, solitary.

• Question posed: What was the most probable nesting behavior of the common ancestor of all gulls?

  • Use of comparative method (phylogenetic reconstruction).

  • Majority rule and phylogenetic position suggest an ancestral ground‐nesting, colonial strategy.

  • Kittiwake viewed as a derived divergence in response to different ecological pressures (cliff habitat, reduced predation).

Convergent vs. Divergent Evolution

• Convergent evolution

  • Distinct ancestry → similar traits.

  • Example: Bank swallows (colonial) & certain gulls exhibit mobbing behavior despite phylogenetic distance.

  • Driven by similar selective pressures (predators, breeding density).

• Divergent evolution

  • Shared ancestry → different traits.

  • Example: Swallow lineage splits into colonial bank swallows vs. solitary rough-winged swallows.

  • Different selective pressures (competition, habitat).

• Selective pressures leading to convergence/divergence

  • Environmental: climate, habitat acoustics.

  • Predation risk.

  • Competition for resources / mates.

  • Mating systems.

Integrative Study of Behavior (Lecture 2 Theme)

• Learning objectives

  • Relate proximate (how) questions to ultimate (why) questions.

  • Understand methodologies that integrate disciplines (endocrinology, genetics, economics).

• Definition of ‘integrative’

  1. Cross-disciplinary tools: hormone assays, molecular parentage, game theory.

  2. Incorporating both Tinbergen’s four levels: mechanism, development, evolutionary history, adaptive function.

Tinbergen’s Four Questions / Levels of Analysis

• Proximate

  • Development (Ontogeny): timing, acquisition.

  • Mechanism (Causation): genetic, neural, hormonal basis.

• Ultimate

  • Evolutionary history (Phylogeny): descent with modification.

  • Adaptive function: fitness value.

• In-class poll: identify examples of proximate vs. ultimate questions.

Bird Song Learning: Taxonomic Scope

• All birds vocalize, but only three clades learn:

  1. Oscine songbirds.

  2. Parrots.

  3. Hummingbirds.

• Implies ≥ 3 independent gains of vocal learning (supported phylogeny shows at least five gains; some uncertainty).

Acoustic Tools to Characterize Song

• Spectrogram / Sonogram

  • X-axis: time, Y-axis: frequency (\text{kHz}) , color/intensity = amplitude.

• Waveform: amplitude vs. time.

• Terminology: syllables, phrases, notes.

• In-class demo: Play bird sound, identify syllables.

Case Study: White-Crowned Sparrow Dialects

Hypotheses for Dialect Formation (non-mutually exclusive)

1. Genetic differences among populations.

2. Acoustic stimulus during development (environmental input).

3. Social interaction with tutors.

Experimental Tests: Acoustic Stimulus Hypothesis

• Isolation rearing

  • Males hatched in lab, raised in soundproof boxes.

  • Began singing ≈ 150\,\text{days} post-hatch.

  • Output: unstructured twitter, nothing like wild song → auditory input necessary.

• Playback of conspecific dialects

  • Fledglings hear a single dialect tape (Marin, Berkeley or Sunset Beach).

  • Adult song matches heard dialect regardless of genetic origin → dialect learnt from environment.

• Playback of heterospecific song (e.g. song sparrow)

  • Results resemble isolation songs; birds ignore alien template.

• Mixed playback (heterospecific + conspecific)

  • Birds select and reproduce ONLY white-crowned sparrow song.

  • Indicates an innate predisposition (template filter).

Experimental Tests: Social Interaction Hypothesis

• Fledglings could hear white-crowned sparrow tape but had live visual/auditory contact with strawberry finch adult males.

• Adult song resembled strawberry finch.

• Conclusion: Social context modulates tutor choice; both sound and social cues critical.

Conclusions

• Dialect development requires:

  • Exposure to acoustic template within sensitive period (\approx 10–50\,\text{days}) .

  • Social reinforcement for tutor selection.

  • Genetic predisposition for conspecific template.

Origins of New Dialects (Hypotheses & Tests)

• Cultural drift: cumulative copy errors.

• Immigrant adults introducing variants.

• Shifts in ambient noise (urban noise, waterfalls).

• Female preference changes.

• Proposed tests: captive translocation, noise-addition, female choice chambers.

Neural Mechanisms (“Song Circuit”)

• Principal nuclei (Fig. 2.6):

  • HVC (High Vocal Center): template storage, integrates feedback.

  • RA (Robust nucleus of the Archopallium): motor output to syrinx.

  • LMAN (Lateral magnocellular nucleus of the Anterior Nidopallium) & Area X: song learning/plasticity.

• Pathways

  • Anterior forebrain loop (HVC → Area X → DLM → LMAN → RA) critical for learning.

  • Motor pathway (HVC → RA → syrinx) critical for production.

• Lesion studies

  • HVC or RA lesions abolish singing ability; LMAN lesions disrupt learning but not adult crystallized song.

• Neuroanatomical dimorphism

  • \text{RA}{\text{male}} \gg \text{RA}{\text{female}} (size & neuron count).

• Neuroplasticity

  • Seasonal and developmental; learning enlarges nuclei (experience-dependent neurogenesis).

Evolution of Song Learning

• Phylogeny (Fig. 2.10) suggests multiple independent gains (✓ marks) and possible losses (✗).

• Genomic convergence with humans

  • Pfenning et al.
    2014: Shared gene-expression modules in human Broca’s/Wernicke’s areas and songbird RA/X.

  • Implies convergent molecular solutions to vocal learning.

Adaptive Value of Song Learning

Benefit-Cost Framework

Sexual Selection Details (Song Sparrow Model)

• Male–male competition

  • Graded signals:

  1. Type match → high aggression.

  2. Shared repertoire (non-matching) → moderate aggression.

  3. Unshared song → low aggression.

  • Number of shared song types positively correlated with male fitness proxy (Beecher 2000).

• Mate attraction

  • Unmated males sing more.

  • Females show phonotaxis & copulation displays toward complex, accurately copied song.

  • Developmental stress paradigm (Fig. 2.18–2.19): females discriminated against nutritionally stressed males (poorer trill bandwidth, syntax).

Costs of Vocal Learning

• Metabolic expense of larger forebrain and song nuclei.

• Extended juvenile period to memorize & practice.

• Exposure to predators while singing/practicing.

Spiral Model of Animal Behavior Research

• Research cycles between proximate and ultimate questions, progressively tightening toward holistic understanding.

• Analogy: tornado spiral—continuous integration of levels & disciplines.

Key Numbers & Facts

• Sensitive period to memorize song: \approx 10–50\,\text{days} (species-specific).

• Crystallization (adult stable song): around 150\,\text{days} in white-crowned sparrow.

• Nutritional stress manipulation: 30 % food reduction during days 0–14 post-hatch.

• Cooperative babbler call repertoire: 13 discrete call types.

Equations / Conceptual Models

• Fitness payoff of song complexity (conceptual):
  W_{male} = f(R, A, C)
  where R = repertoire size, A = accuracy/quality, C = context (competition, habitat).

• Trade-off between brain cost and signaling benefit:
  \Delta W = B{signal} - C{brain}
  Vocal learning evolves when \Delta W > 0 under given ecological/social conditions.

Ethical, Philosophical, Practical Notes

• Research often involves isolation of juveniles; animal welfare protocols mandate minimal stress & enriched environments.

• Vocal learning studies inform human language evolution, speech disorders, and neuroplasticity—bridging biology & medicine.

• Noise pollution’s impact on song learning links behavioral ecology with conservation policy.

Connections to Other Lectures / Principles

• Revisits comparative method first introduced with gull nesting.

• Demonstrates Tinbergen framework throughout (proximate brain mechanisms ↔ ultimate adaptive function).

• Integrates evolutionary concepts (convergence/divergence) with mechanistic neuroscience—hallmark of integrative biology.