Ornithology: Bird Vocalizations Notes

Sound Defined: Vibration-generated waves of air pressure that can be heard; vary in pitch and loudness.
Two major ways to differentiate sounds:
- Frequency/Pitch:
  - Measures rate at which sound is produced.
  - Measured in cycles per second (Hz = hertz or kHz = kilohertz).
  - Low vs. High pitch notes.
- Amplitude/Loudness:
  - Measures intensity of vibration-generated waves of air pressure.
  - Measured in decibels.
  - Louder vs. quieter notes.
Frequency vs. Amplitude:
- Low Pitch Sounds:
  - Travel farther distances.
  - Travel better through physical obstacles.
  - Difficult to triangulate.
- High Pitch Sounds:
  - Travel shorter distances.
  - Don't travel well through physical obstacles.
  - Easier to triangulate.
- Loud Sounds:
  - More easily heard/noticed.
  - Travel farther distances.
- Quiet Sounds:
  - More difficult to hear/notice.
  - Travel shorter distances.

"Pictures of vocalizations".
Allow us to "see" vocalizations.
Hearing + seeing make identification much easier!
Seeing helps us notice intricacies in vocalizations that we might not notice with our ears; changes our perception of the sounds we're hearing.
Sonagram (aka Spectrogram):
- Sound plotted as frequency (kHz) over time (seconds).
Oscillogram:
- Sound plotted as relative loudness (i.e., air wave pressure) in micropascals or decibels over time in seconds; no indication of frequency.

Virtually all birds vocalize, but bird groups vary greatly in vocalization frequency, complexity, and diversity.
As a rule, passerines, specifically oscine passerines, hummingbirds, and parrots have the most complex vocalizations and the most extensive repertoires
Generally, larger birds have simpler sounds and repertoires (except parrots and the Lyrebird); smaller birds have greater vocalization frequency, complexity, and diversity
Most suboscine passerines make 5-14 distinct vocalizations, some possibly 100s!
The Chaffinch of Europe (subject of many vocalization studies) has many different vocalizations in its repertoire:
- Flight Call
- Social aka Contact Call
- Injury Call
- Aggression Call
- Alarm Calls
- Courtship Calls
- Subsong
- Song
- About half used only in breeding season, other half used year-round.

Songs:
- Longer, more complex vocalizations
- Under hormonal control (note: courtship calls also hormonal)
- Used in sexual selection (usually males only)
- Mostly used by males for maintaining territory and attracting females
$Day Length \uparrow$
$Gonad Size \uparrow$
$Hormone Production \uparrow$
$Song Control Centers in Brain Stimulated$
$Singing Rate \uparrow$
LATE WINTER --> EARLY SPRING --> LATE SPRING
Most Calls:
- Generally shorter, less complex vocalizations used by both sexes
  *Coordinate behaviors like territorial defense, alarms/warnings, mobbing, courtship,
  copulation, begging/feeding, contact, and group cohesion.

Most vocalizations of most species are innate - i.e., Completely genetic; inherited fully formed
However, roughly half of all species learn their songs (at least partly) - i.e., Hummingbirds (=350spp), Parrots (=400spp), and oscine Passerines (=4500spp)
- Many of these species inherit a basic template of their species' song
- However, different regional dialects often exist in species (especially those with large ranges)
  - Dialects must be learned.

Hatched and raised naïve male WCSPs in sound-proof chambers
Juveniles never heard any adult vocalizations until they heard recordings in chambers
Exposed juvenile birds to various conditions and observed their vocalizations at adulthood:
- Condition 1: Played no songs or vocalizations
  - Result: Test subjects sang a simplified version (i.e., template) of their species' song!
- Condition 2: Played song dialect of test subject's population of origin
  - Result: Test subjects sang dialect of their population!
- Condition 3: Played foreign song dialect that differed from test subject's population of origin
  - Result: Test subjects sang foreign dialect!
- Condition 4: Played songs from Song Sparrows
  - Result: Test subjects sang a simplified version (i.e., template) of their species' song!
- Conclusion: Songs are partially innate, but dialects are learned by listening to conspecifics!

Most tetrapods use a larynx to vocalize, but not birds…
In birds, larynx has similar function to mammalian epiglottis
In some birds, also plays roles in vocalization modulation (varying pitch and amplitude)
For vocalizations, birds have a syrinx…
- Specialized vocalization organ located at the bifurcation of the primary bronchi
- In many birds, it can make two independent sounds at once!
Humans use $=2\%$ of exhaled air to make sound! Birds use 100%! Bird vocals are loud!!!

Wood Thrush: Simultaneous Output from Two Syrinxes
Simple Syrinx
- Medial bronchial membrane
- All non-passerines and (=1000) suboscine passerines (e.g., flycatchers)
Complex Syrinx
- Oscine Passerines: more muscle for more control of complex vibrations = more complex vocalizations
Syrinx musculature compared in Oscine vs Suboscine Passerines

Pileated Woodpecker Drumming: https://youtube.com/shorts/HSrV3BCc92E?feature=shared
Ruffed Grouse Drumming: https://www.youtube.com/watch?v=MVfilp3QGS4
White-collared Manakin Lek: https://www.youtube.com/watch?v=d6gY63UKPYc
Anna's Hummingbird Male Courtship Dive with Spread Out Tail Feathers: https://www.youtube.com/watch?v=mbJvxH2dyGU
How Club-winged Manakins "Call" with Modified Secondary Feather Shafts (Stridulation): https://www.youtube.com/watch?v=15YAo5-jM4g&t=52s