Ornithology Final

Biological vs. Phylogenetic Species Concepts (PSC)

Biological Species Concept (BSC): Defines species as groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups.

• Strengths: Closely tied to evolutionary processes (gene flow, reproductive isolation); useful for studying speciation in sexually reproducing birds.

• Weaknesses: Difficult to apply to allopatric populations, fossils, and asexual organisms; hybridization in birds (e.g., ducks, gulls) blurs species boundaries.

Phylogenetic Species Concept (PSC): Defines species as the smallest diagnosable monophyletic groups sharing a common ancestor.

• Strengths: Applicable to fossils and allopatric populations; uses genetic and morphological data; aligns well with modern molecular systematics.

• Weaknesses: Can lead to taxonomic inflation (splitting); may overemphasize minor differences with limited ecological significance.

Evolution of Birds from Reptiles: Two Hypotheses

The Theropod Dinosaur Hypothesis (Consensus View):

• Birds evolved from small, feathered theropod dinosaurs (e.g., Velociraptor relatives).

• Feathers evolved before flight, likely for insulation, display, or brooding.

• Archaeopteryx (~150 MYA) shows a mix of reptilian and avian traits.

The Thecodont / Early Archosaur Hypothesis:

• Proposes birds evolved earlier from basal archosaurs, with flight evolving independently of dinosaurs.

• Less supported by fossil and molecular evidence.

Importance of Systematics and Taxonomy for Conservation

Systematics and taxonomy provide essential frameworks for identifying and classifying species, which is crucial for conservation efforts. Understanding evolutionary relationships helps prioritize biodiversity conservation and manage ecosystems effectively.

Bernoulli’s Principle and Powered Flight

Bernoulli’s principle states that faster-moving air has lower pressure.

• Bird wings are airfoils: air moves faster over the curved upper surface, creating lift.

• Lift is also generated by Newton’s laws: wings deflect air downward, producing an equal and opposite upward force.

• Powered flight requires thrust (from flapping), lift, drag reduction, and weight support.

Pectoral Girdle and Flight Muscles

• Key bones: Furcula (wishbone), coracoid, scapula, and keeled sternum.

• Pectoralis major: Powers downstroke (main source of lift and thrust).

• Supracoracoideus: Powers upstroke via a pulley-like tendon through the triosseal canal.

• Adaptations maximize force production while minimizing weight.

Plumages and Molt Strategies

 

• Plumages: Juvenile, basic (non-breeding), alternate (breeding), eclipse (ducks).

• Molts:

  • Prebasic molt: replaces feathers annually.

  • Prealternate molt: partial molt for breeding plumage.

• Strategies vary by ecology, migration, and sexual selection.

Food Resources and Clutch Size

• Precocial species: Clutch size limited by female’s ability to produce eggs (pre-laying resources).

• Altricial species: Clutch size limited by ability to provision chicks after hatching.

• Determinate layers: Fixed clutch size.

• Indeterminate layers: Adjust clutch size based on food availability.

Lack’s Hypothesis

Lack proposed that clutch size is optimized to maximize the number of surviving offspring.

• In indeterminate layers, females adjust egg number to food availability.

• Females lay fewer eggs than predicted due to costs to future survival or reproduction.

Mimicry in Birds

• Predator avoidance hypothesis: Mimicking dangerous species reduces predation (e.g., hawk-like plumage in cuckoos).

• Acoustic interference hypothesis: Mimicry disrupts competitor communication (e.g., lyrebirds).

Cooperative Breeding Experiment

Hypothesis: Cooperative breeding evolves due to ecological constraints (lack of territories).

• Experiment: Compare territory availability and helper presence across habitats.

• Prediction: Helpers are more common where territory availability is low.

Polyandry

• Rare due to high female reproductive costs.

• Occurs when males provide most parental care (e.g., jacanas).

• Traits: sex-role reversal, female aggression, male-only incubation.

Calls vs. Songs

• Calls: Short, simple, innate; used year-round for alarms or contact.

• Songs: Complex, learned; primarily used in breeding for mate attraction and territory defense.

Population, Community, Guild, Niche

• Population: Same species in an area (e.g., Bald Eagles in Alaska).

• Community: All species in an area.

• Guild: Species using similar resources (e.g., aerial insectivores).

• Niche: Species’ role and resource use.

Species of Conservation Concern: California Condor

• Threats: Lead poisoning, habitat loss, collisions.

• Management: Captive breeding, lead ammo bans, tracking.

Endemic Bird Areas (EBAs)

Regions with high concentrations of range-restricted species; used to prioritize global conservation efforts.

Birds Prone to Extinction

• Island endemism: Hawaiian honeycreepers.

• Specialized niches: Spotted Owl dependent on old-growth forests.

Bird Conservation Law: Migratory Bird Treaty Act

• Protects migratory birds from take.

• Strengths: Broad protection.

Weaknesses: Limited habitat protection.

Realized and fundamental niches

Realized Niche- Resources used by a species set by real-world limitations.

Fundamental Niche- Ideal set of conditions for a species to live and reproduce