Lecture+7-+Sensory+Systems

Sensory Systems Overview

• Birds perceive their environment differently than humans.

  • Ability to see into the UV spectrum.

  • Capable of detecting:

    • Magnetism

    • Polarized light

    • Celestial compasses

    • Gravity

    • Barometric pressure

• Display advanced intelligence compared to most mammals:

  • Exhibit language, culture, and tool use.

  • Possess advanced spatial memory.

Eye Structure and Function

Eye Size

• Large prominent eyes are common in birds.

  • Example: European Starling's eyes make up 15% of head mass.

Vision Mechanics

• Bird eyes are usually located on the sides of their heads.

• They often use one eye at a time for better object examination.

• Birds move their heads rapidly to gain different perspectives.

  • Example: The head bobbing behavior seen in pigeons.

Eye Anatomy

• Key structures:

  • Cornea

  • Lens: Changes curvature; unique in some species.

  • Sclera, Choroid, Retina

  • Pecten: Theories suggest it provides nutrition and oxygen to the retina, which lacks embedded blood vessels.

• Detailed feature of birds' vision:

  • High density of cones for color vision:

    • Humans: ~200,000 cones/mm²

    • House Sparrow: ~400,000 cones/mm²

    • Common Buzzard: ~1,000,000 cones/mm²

• Birds have a deep central fovea enhancing visual acuity and motion detection (100 hz sensitivity).

Color Vision

• Early mammals lost colored oil droplets due to nocturnal evolution.

• Birds retain ancestral oil droplets, leading to enhanced color vision, including sensitivity to near UV light.

Magnetism and Navigation

• Mechanisms of detecting magnetic fields in birds are still under research.

• Possible theories include:

  • Presence of magnetite-like elements in birds' heads.

  • Photopigment rhodopsin's ability to translate light and magnetic fields into nerve impulses.

• The avian retina responds to magnetic stimulation; pineal gland may also contain magnetite.

Hearing Adaptations

Ear Structure

• External Ear: Located behind and below the eye, protected by auricular feathers.

• Middle Ear: Contains one ear bone (columella/stapes) associated with sound transmission.

• Inner Ear: Houses a fluid-filled cochlea involved in sound processing.

Hearing Capabilities

• Birds have varying sensitivity to sound.

  • Generally, humans can hear fainter sounds than birds at most frequencies.

  • Certain birds (e.g., pigeons, chickens) are sensitive to low frequencies.

  • Birds generally have a lower ability to hear higher frequencies compared to humans.

Touch and Mechanoreception

• Touch:

  • Herbst corpuscle: Senses slight pressure changes; found in sensitive bill tips.

• Birds also have mechanisms to detect:

  • Equilibrium

  • Barometric pressure changes.

Bird Brain Anatomy

• Proportionally larger brains (2-9% of body mass) compared to similar-sized reptiles.

• Notable species include:

  • Parrots, owls, crows, woodpeckers, hornbills (notable for size and intelligence).

Brain Structure Highlights

• Advanced mid- and forebrain development.

• Large optic lobes and cerebellum enhance balance and coordination.

• Lateralization: Birds exhibit side dominance, similar to humans.

Cognitive Abilities

Memory and Intelligence

• Hippocampus: Similar to mammals, aiding in spatial orientation and memory retention.

• Example Species:

  • Corvidae (nutcrackers, crows, and jays): Known for seed storage and memory capabilities.

  • Nutcrackers can remember locations of up to 30,000 pine seeds across 9 months.

Learning and Adaptation

• New synapses formed when needed, as seen in songbirds:

  • Canaries learn new songs in spring; synapses decrease in fall.

  • Chickadees can increase hippocampus volume by 30% in autumn to enhance memory.

Sleep Patterns

• Birds experience three stages of sleep (similar to mammals):

  • Slow-wave sleep: Unihemispheric sleep, allowing them to rest one eye at a time (e.g., Sooty Terns can sleep while flying).

  • Intermediate sleep

  • Rapid Eye Movement (REM) sleep: Quick episodes, with evidence of dreaming (e.g., Zebra finches dreaming about songs).

Cognition in Birds

• Counting Ability: Birds can count effectively (up to 7).

• Art Critique: Ability of pigeons to distinguish between different art styles (e.g., cubism vs. impressionism).

Examples of Cleverness

• Various examples of problem-solving behavior include fishing techniques in herons and creative problem-solving in crows.