Ornithology Ex2 P2

What are the three main mating systems in birds, and how common are they?

• Monogamy: One male + one female form a pair bond for one or more breeding seasons. Most common (≈90% of species). “Divorce” can occur.

• Polygyny: One male mates with multiple females. Uncommon (≈2–5% of species). Leads to sexual dimorphism and strong male competition.

• Polyandry: One female mates with multiple males. Rare (≈1% of species). Found in species with reversed sex roles.

What is the difference between genetic and social monogamy?

• Social monogamy: A male and female form a social pair bond and raise offspring together, but may mate outside the pair.

• Genetic monogamy: A female mates only with one male, and all offspring are genetically his.
  Most birds are socially, not genetically, monogamous.

What are extra-pair copulations and extra-pair paternity, and what are their pros and cons?

• Extra-pair copulation (EPC): Mating between individuals not pair-bonded together.

• Extra-pair paternity (EPP): When a chick in a nest is sired by a male other than the social father. (father that raises chick isn’t the biological father)
  
  For females:
  Pros: Gain “good genes” for offspring, fertility insurance (avoids infertile mates), possibly more resources or protection.
  Cons: Risk of mate abandonment, conflict, or injury from extra mating.

  For males:
  Pros: Can father extra offspring without parental investment.
  Cons: Risk of raising offspring that aren’t theirs (EPP), reduced paternity confidence.

What is same-sex pairing in birds, and how has it evolved?

• Occurs when individuals of the same sex (often females) form pair bonds—common when males are scarce.

• Pairs may still solicit matings from nearby males.

• Can be lifelong (e.g., Laysan Albatross).

• Likely evolved from social bonding flexibility and strong parental cooperation behaviors seen in birds, allowing same-sex pairs to successfully share nesting and chick-rearing duties.

What are the main reasons for the evolution of polygyny, and what are its types?

• Evolved when males can increase fitness by mating with multiple females.
  Types:

1. Resource defense polygyny: Male defends a high-quality territory or resource that attracts multiple females (common when resources are clumped).

2. Female defense polygyny: Male defends a group of females directly (common in species nesting in clusters, like “harems”).

3. Male dominance polygyny: Males gather and display, and females choose the dominant male (leads to strong sexual selection).

What are the reasons for the evolution of polyandry, and what are its types?

• Evolved in species where males provide most parental care or nest sites/ High nest predation.
  Types:

1. Sequential polyandry: Female mates with one male, lays eggs, leaves him to tend them, and mates again elsewhere (e.g., Sanderling). Not overlapping

2. Simultaneous polyandry: Female holds a large territory with several males; each builds a nest and cares for young. Overlapping

3. Cooperative simultaneous polyandry: Several males share one female and help raise one nest together (2–8 males).

What is lekking?

• Lekking = males gather in a specific area (a lek) to perform competitive displays for visiting females.

• Females watch and choose mates based on display quality.

• Leads to strong sexual selection and extreme male ornamentation or dances (e.g., sage grouse, manakins).

What is brood parasitism?

• A bird lays its eggs in another species’ nest instead of building its own.

• The host is tricked into raising the parasite’s chicks.

• Seen in species that may be monogamous, polygynous, or polyandrous.

• Evolved to save energy and increase reproductive output.

• Example: Brown-headed Cowbird, Common Cuckoo.

What is pair bonding and how is it reinforced?

• A pair bond forms between mates, often in socially monogamous species.

• Reinforced through:

  • Allopreening (mutual grooming)

  • Gift-giving or item presentation

  • Courtship feeding

• Helps maintain cooperation and strengthens reproductive success.

What is the difference between a bird’s song and a call?

• Song:

  • Long, repeated, often musical pattern

  • Usually by males

  • Used for mate attraction and territory defense

• Call:

  • Short, simple vocalization

  • Given by both sexes

  • Used for communication like alarm, contact, or flight

What are the main functions of bird song?

• Attract a mate

• Defend or claim a territory

• Signal location to others

• Allow species and sex recognition

What are the different types of bird calls and their functions?

• Contact call: Keeps flock members in touch; used to maintain social contact. (General Communication)

• Alarm/mobbing call: Warns others of predators.

  • Early alarm calls = short, high-pitched (hard to locate).

  • Mobbing calls = loud, harsh (warns predator it’s been spotted).

• Begging call: Given by chicks (and sometimes females) to elicit feeding.

• Flight call: Short call given during long flights (especially migration); helps maintain group contact. (Purpose: coordinate group movement, maintain spacing, and signal direction or readiness to land.)

How do vocal signals and song structure relate to the environment?

• Songs adapt to travel best in each habitat:

  • Dense forests: Lower frequencies, (longer wavelength) slower notes (carry through vegetation).

  • Open habitats: Higher frequencies (shorter wavelength), rapid notes (carry in open air), more prone to disruption

• Sound travels around and through obstacles.

• Can be used while doing other tasks.

• Conveys lots of information quickly and over long distances.

What are examples of non-vocal sound production in birds?

• Feather sounds: Vibrating wing or tail feathers make noises during flight or displays (e.g., manakins, doves, snipes).

• Woodpecker drumming: Beak tapping used for territory or attracting mates.

• Wing or air sounds: Hummingbirds or pigeons make whooshing or humming as they fly.

• Some are signals, others are just movement by-products that became communication tools.

How does the syrinx work, and how can birds make two sounds at once?

Syrinx:
The sound-producing organ located where the trachea splits into the two bronchi. Air passing through makes membranes vibrate to create sound.

Muscles:

• Ratites, storks, vultures: No functional syringeal muscles → limited sound control.

• Most non-passerines: About 2 pairs of syringeal muscles → moderate control.

• Songbirds (oscine passerines): Up to 6 pairs of syringeal muscles → fine control and complex songs.

Two-sound ability:
Each bronchus can vibrate independently, and songbirds can control both sides separately, allowing them to produce two different notes at once.

How does song learning work in birds without innate songs? (bird must learn song from experience)

Birds without innate songs must learn their songs by hearing and practicing them — unlike species born knowing their song.

1. Sensory acquisition phase:
The young bird listens to adult “tutor” songs and memorizes them. This is when the template for the song is formed.

2. Silent period:
The bird doesn’t sing yet — it just keeps the memory of the song in its brain, waiting until its vocal muscles develop more.

3. Sensorimotor phase:
The bird starts to practice the song (called a “plastic song”). It compares what it sings to the memorized model and adjusts using auditory feedback.

4. Song crystallization:
After much practice, the song becomes clear, consistent, and matches the memorized template. This is the final “adult song.”

How does song learning lead to vocal dialects?

• Young birds learn songs by imitating adults (usually males) in their natal area during the song learning stages.

• Because learning is cultural, not genetic, small differences in songs can develop between regions or groups.

• Over generations, these differences accumulate, forming distinct local “dialects.”

• Dialects can help birds attract mates familiar with that song type and signal local identity to neighbors.

• Example: White-crowned Sparrows show clear regional dialects depending on where they were raised.

What is vocal mimicry, and why do some birds do it?

• Copying sounds or songs from other species or noises.

• Seen in about 20% of passerines (e.g., mockingbirds, lyrebirds).
  Functions:

  • Increases song repertoire (helps attract mates).

  • May confuse or deter rivals.

  • Shows learning ability and fitness.

What is dueting, and what is its function?

Dueting: Coordinated singing between mates.
Functions:

• Strengthens pair bond.

• Maintains contact or reveals location to mate.

• May also help defend shared territory.

What is the dawn chorus, and why do birds sing at this time?

Dawn chorus: Period just before and after sunrise when many birds sing.
Reasons:

• Easier to sing in calm, quiet air (less wind).

• Fewer predators active.

• Visibility is low, so sound is the best way to communicate.

• Feeding is less efficient early (dew, low prey activity), so they use the time to advertise territory and attract mates.

What is the role of visual signaling in birds, and how does it differ from vocal signaling?

• Visual signaling = communication through sight (color, shape, movement).

• Transfers information about identity, sex, mood, or fitness.

• Works best in good light and open habitats.

• Compared to vocal signals:

  • Visual = immediate, short-range, requires visibility.

  • Vocal = long-range, can work around obstacles or in darkness.

What are common types of visual signals in birds?

• Bright coloration (e.g., plumage or skin color) — shows health, species, or sex.

• Posture and body shape — used in displays to look larger or more dominant.

• Movements — wing flicking, tail fanning, or bowing during courtship.

• Feather ornaments — crests, tails, or wattles that draw attention.

What is ritualization, and how can it lead to visual display evolution?

Ritualization: When a behavior that originally had a practical function (like feeding or aggression) becomes exaggerated and symbolic, used mainly for communication.
-behavior with one function becomes used for another function

Natural movements become stylized to send information — often evolving into visual displays.

Examples:

• Aggression → Courtship: Threat movements (like head-raising or bowing) become softer courtship gestures.

• Nest building → Courtship: Offering twigs or nest materials signals quality or commitment.

• Foraging → Display: Feeding motions (like pecking) become symbolic gestures showing energy or coordination.

Over time, these ritualized actions turn into ornamental displays for attraction or dominance.

How does sexual selection drive the evolution of visual signals?

• Sexual selection favors traits that increase mating success, even if they reduce survival.

• Leads to the evolution of:

  • Courtship displays: Dances, bowing, or spreading plumage to attract mates.

  • Bright plumage: Indicates good health or strong genetics (e.g., carotenoid-based reds/yellows).

  • Ornaments: Long tails, crests, wattles — often more elaborate in males.

• Females often choose males with the best displays → reinforces these traits over generations.

• Example: Peacock’s tail evolved through female choice for elaborate feathers.

What are some non-sexual uses of visual signaling in birds?

Non-sexual visual signals = communication about survival, safety, and resource control — not about attracting mates.

• Aggression and dominance: Raised feathers or spread wings show strength.

• Feeding behavior: Used to coordinate group foraging.

• Parent-offspring communication: Chicks open bright mouths to stimulate feeding.

• Territory defense: Displaying bright plumage or postures to warn intruders.