Social Behavior in Birds

Social Behavior

• Some birds are solitary for most of their lives.

• Others exist in pairs.

• Many pair briefly for breeding, then become gregarious.

• Still others live in social groups their entire lives.

Types of Social Behavior

• Territoriality

• Dominance hierarchies

  • Colonies

  • Flocking

• Examples:

  • Olrog's Gulls

  • Northern Mockingbird

Territoriality

• A form of aggression where individuals exclude conspecifics or other species from resources.

• Example species: Campo Flicker (Colaptes campestris)

Territories

• Area defended by one or more individuals against intrusion.

• Defending a high-quality territory assures greater resources (food, nest sites).

• Territories can be temporary or permanent.

  • Migratory birds establish territories during the breeding season (e.g., Swainson’s Warbler).

  • Shorebirds defend areas for a few hours or days during migration.

Swainson’s Warbler Territory & Home Range

• Minimum Convex Polygon estimate vs. 95% Fixed Kernel Estimate.

• Territory (white area; singing locations) was 6.7 ha or 75.4% of home range size, 8.8 ha (gray area).

• Visual territory mapping versus radio telemetry estimates of Swainson’s Warbler territory size.

• Few “intrusions” (10.8%) & little overlap.

Resource for Space

• Nesting.

• Mate attraction.

• Food accumulation.

Benefits of Territorial Behavior

• Resources for individual health.

• Health of mates and offspring.

• Breeding success and increased fitness.

Costs of Territorial Behavior

• Energy and time for defense.

• Increased predation threat.

• Physical injury, infection, death.

• Territorial behavior arises when benefits outweigh the costs.

Two Classes of Territory

1. Breeding

2. Non-breeding

Breeding Territories

• Multipurpose Territories - all purpose, including food, nesting, courtship, etc.

• Tends to increase in size with body weight.

• Individuals adjust territory size depending on resources, e.g., Pomarine Jaegers territories go from 19 to 45 ha when lemmings are low in abundance.

• Limited Territory - defense of one resource (e.g., cavity or mate).

• Leks (communal display grounds) - For mate attraction and act of mating.

Non-breeding territories

• Roosting Territory - nocturnal security (Starlings).

• Feeding Territory - (nectar hummingbirds).

• Personal Space Territory – nocturnal security.

Economically Defendable Territory

• Energy available in a territory should not be less than energy expended in territory defense.

• Territorial sunbirds:

  • Saved 1.3 hours of foraging time per day, or about 780 cal/day.

  • Expended about 730 cal/day in defending territories.

  • Made a small energy 'profit' (benefits > costs).

• Territories of intermediate sizes are economically defensible because the benefits exceed the costs.

Coloniality

• Birds nesting in large numbers & high densities in small spatial areas (~13% of all species, many seabirds).

• Evolved due to:

  • Shortage of nesting sites safe from predators.

  • Abundant or unpredictable food distant from safe nest sites.

Benefits of Living in a Group

• Safer in colonies inaccessible to predators.

• Groups of birds detect predators more quickly.

• Synchronizing nesting produces abundant eggs & young that swamps local predators (predator swamping).

• Improved foraging - “Information Center Hypothesis”.

  • e.g., Cliff Swallows, Ospreys, Bald Eagles.

  • Knight and Knight. 1983. Auk 100:477-484. Bald Eagle Roosts as Information Centers

    • 22.2% of departing eagles (n = 473) classified as followers compared to 11.1% of arriving eagles (n = 771)

    • Immature eagles more likely to be followers (17.6%) than adults (11.2%)

    • Adults more likely to be leaders (18.9%) than immatures (8.7%)

Flock Feeding

• Foraging benefits.

• The “Beater Effect”.

• Cooperation – e.g., pelicans.

• 2 advantages:

  • Information sharing.

  • Producer‐scrounger.

Cooperative Hunting in Harris' Hawks

• Harris’s Hawk Optimization Algorithm

Harris’ Hawks

• The larger the HAHA group, the more lagomorph kills/50 hr

• Mean energy requirements for individual hawks = 147.8 kcal/day

• Individual energetic benefits stabilize at a group size of 5 hawks (148.1 kcal/day)

• Mean group size observed during the non‐breeding season = 4.8 hawks (mode = 5 hawks)

• The benefits of the team hunts by HAHAs in New Mexico are key to the evolution and maintenance of their social living strategy.

Costs of Living in a Group

• Need to share resources.

• Increased physical intraspecific interference.

• Competition for nest sites & stealing of nest materials (European rollers).

• Increased competition for mates.

• Loss of paternity.

• Attract predators.

• Risk of parasites (bird mite, blowfly larvae, Plasmodium, Trypanosoma).

Heritable Basis for Choice of Group Size

• The Browns switched ~2,000 young birds from nests in big colonies to nests in small colonies (& reverse), & discovered that these birds chose the same colony size as that in which they were hatched.

• Suggests a genetic difference between birds that choose to live in large groups versus small colonies.

• They return to where they were born irrespective of where they were raised.

• They are picking the colonies that their parents picked; so it is not environment, it is genes that appear to be dictating their choice.

Flocking

• An aggregation of large numbers of individuals within a species often outside of the breeding season.

• Causes - opposite to circumstance which promotes territoriality, when resources are unstable.

Benefits of Flocking

• Reduces the threat of predation.

  • Merlins have better success foraging on shorebirds when flocks are smaller.

Costs of Flocking

• Dominance hierarchy within flocks (Harris Sparrows - dominance indicated by black-markings).

• Increased competition for limited food supplies, increased risk of disease, and increased aggression to maintain individual distances.

• Work by Caraco suggests there should be an optimal, or intermediate, flock size due to trade-offs between: feeding, fighting, scanning for predators.

• Joining a flock theoretically decreases the risk of being caught and eaten, because there is safety in numbers.

• Yellow-eyed junco

  • Average flock size increased from 3.9 to 7.3 juncos when a Harris‘s Hawk regularly flew over the feeding grounds (Caraco et al. 1980).

Mixed-Species Flocks

• Many tropical birds live almost their entire lives in mixed-species flocks.

• Sympatric flocking species often shared distinctive plumage patterns.

Advantages of Staying Together in Flocks

• Is it possible that there are local “dialects” of flocking signals?

Hierarchy of Interspecific Dominance Among Birds That Follow Army Ants

• Ocellated antbird (A)

• Bicolored antbird (B)

• Spotted antbird (C)

• White-plumed antbird (C)

• Mixed flocks in temperate regions too.

• The tension between trying to eat while avoiding being eaten is central to avian social behavior.

• The defensibility of a given space, the variability of food resources, and the probability of attack determine spatial relations and social behavior.

Social Behavior

• Some birds exhibit solitary behavior throughout most of their lives, preferring to live and forage alone.

• Others exist in pairs, often forming strong bonds for companionship and cooperative activities.

• Many pair briefly for breeding purposes, engaging in courtship rituals and nesting before reverting to gregarious behavior.

• Still others live in complex social groups their entire lives, forming intricate relationships and hierarchies.

Types of Social Behavior

• Territoriality: Defending a specific area against intrusion from others.

• Dominance hierarchies: Establishing a pecking order within a group.

• Colonies: Forming large aggregations for nesting and protection.

  • Flocking: Gathering in large groups for foraging and safety.

• Examples:

  • Olrog's Gulls: Known for their colonial nesting behavior.

  • Northern Mockingbird: Often territorial and solitary.

Territoriality

• A form of aggression where individuals exclude conspecifics or other species from resources, such as food, mates, or nesting sites.

• Example species: Campo Flicker (Colaptes\ campestris). This bird actively defends its territory from intruders.

Territories

• Area defended by one or more individuals against intrusion, ensuring exclusive access to essential resources.

• Defending a high-quality territory assures greater resources (food, nest sites), increasing the chances of survival and reproductive success.

• Territories can be temporary or permanent.

  • Migratory birds establish territories during the breeding season (e.g., Swainson’s Warbler), securing areas for nesting and raising offspring.

  • Shorebirds defend areas for a few hours or days during migration, utilizing temporary feeding grounds along their journey.

Swainson’s Warbler Territory & Home Range

• Minimum Convex Polygon estimate vs. 95% Fixed Kernel Estimate.

• Territory (white area; singing locations) was 6.7 ha or 75.4% of home range size, 8.8 ha (gray area).

• Visual territory mapping versus radio telemetry estimates of Swainson’s Warbler territory size.

• Few “intrusions” (10.8%) & little overlap.

Resource for Space

• Nesting: Securing a safe and suitable location for building nests and raising young.

• Mate attraction: Utilizing the territory to attract potential mates through displays and vocalizations.

• Food accumulation: Ensuring a consistent supply of food for personal consumption and feeding offspring.

Benefits of Territorial Behavior

• Resources for individual health: Access to food and shelter promotes overall well-being.

• Health of mates and offspring: Ensuring the health and survival of family members.

• Breeding success and increased fitness: Maximizing reproductive output and passing on genes to future generations.

Costs of Territorial Behavior

• Energy and time for defense: Expending valuable resources on patrolling and defending the territory.

• Increased predation threat: Drawing attention to oneself and becoming vulnerable to predators.

• Physical injury, infection, death: Risking harm in confrontations with rivals or predators.

• Territorial behavior arises when benefits outweigh the costs, indicating an evolutionary adaptation.

Two Classes of Territory

1. Breeding: Territories established for reproductive purposes.

2. Non-breeding: Territories used for activities other than breeding.

Breeding Territories

• Multipurpose Territories - all purpose, including food, nesting, courtship, etc.

• Tends to increase in size with body weight; larger birds require larger territories to meet their resource needs.

• Individuals adjust territory size depending on resources, e.g., Pomarine Jaegers territories go from 19 to 45 ha when lemmings are low in abundance, reflecting the need to secure sufficient food.

• Limited Territory - defense of one resource (e.g., cavity or mate), focusing on protecting a specific essential item.

• Leks (communal display grounds) - For mate attraction and act of mating, serving as central locations for courtship rituals.

Non-breeding territories

• Roosting Territory - nocturnal security (Starlings), providing a safe place to rest and avoid predators during the night.

• Feeding Territory - (nectar hummingbirds), ensuring exclusive access to food sources.

• Personal Space Territory – nocturnal security, maintaining a buffer zone around individuals for comfort and safety.

Economically Defendable Territory

• Energy available in a territory should not be less than energy expended in territory defense, maintaining a positive energy balance.

• Territorial sunbirds:

  • Saved 1.3 hours of foraging time per day, or about 780 cal/day, demonstrating the efficiency of defending a resource-rich territory.

  • Expended about 730 cal/day in defending territories, showcasing the energy investment required for territorial defense.

  • Made a small energy 'profit' (benefits > costs), illustrating the economic advantage of territoriality.

• Territories of intermediate sizes are economically defensible because the benefits exceed the costs, optimizing resource acquisition and energy expenditure.

Coloniality

• Birds nesting in large numbers & high densities in small spatial areas (~13% of all species, many seabirds), forming tightly packed communities.

• Evolved due to:

  • Shortage of nesting sites safe from predators, driving birds to congregate in secure locations.

  • Abundant or unpredictable food distant from safe nest sites, necessitating communal living to exploit resources efficiently.

Benefits of Living in a Group

• Safer in colonies inaccessible to predators, reducing the risk of individual predation.

• Groups of birds detect predators more quickly, enhancing vigilance and early warning systems.

• Synchronizing nesting produces abundant eggs & young that swamps local predators (predator swamping), overwhelming predator populations with sheer numbers.

• Improved foraging - “Information Center Hypothesis”:

  • e.g., Cliff Swallows, Ospreys, Bald Eagles, which use communal roosts to share information about food sources.

  • Knight and Knight. 1983. Auk 100:477-484. Bald Eagle Roosts as Information Centers.

    • 22.2% of departing eagles (n = 473) classified as followers compared to 11.1% of arriving eagles (n = 771), indicating information sharing at roosts.

    • Immature eagles more likely to be followers (17.6%) than adults (11.2%), suggesting learning from experienced individuals.

    • Adults more likely to be leaders (18.9%) than immatures (8.7%), highlighting the role of experienced birds in guiding foraging efforts.

Flock Feeding

• Foraging benefits: Increased efficiency in finding and capturing food.

• The “Beater Effect”: Driving prey out of hiding through coordinated movements.

• Cooperation – e.g., pelicans: Working together to corral fish into shallow waters.

• 2 advantages:

  • Information sharing: Learning about food locations from other flock members.

  • Producer‐scrounger: Individuals either find food (producers) or steal it from others (scroungers).

Cooperative Hunting in Harris' Hawks

• Harris’s Hawk Optimization Algorithm: A sophisticated strategy for hunting in groups.

Harris’ Hawks

• The larger the HAHA group, the more lagomorph kills/50 hr, indicating enhanced hunting success with larger group sizes.

• Mean energy requirements for individual hawks = 147.8 kcal/day, representing baseline energy needs.

• Individual energetic benefits stabilize at a group size of 5 hawks (148.1 kcal/day), optimizing energy intake per individual.

• Mean group size observed during the non‐breeding season = 4.8 hawks (mode = 5 hawks), reflecting the balance between group size and individual benefits.

• The benefits of the team hunts by HAHAs in New Mexico are key to the evolution and maintenance of their social living strategy, highlighting the importance of cooperative behavior.

Costs of Living in a Group

• Need to share resources: Competition for limited food and nesting sites.

• Increased physical intraspecific interference: Aggression and conflict among group members.

• Competition for nest sites & stealing of nest materials (European rollers): Resource-related conflicts within the group.

• Increased competition for mates: Intense rivalry for reproductive opportunities.

• Loss of paternity: Uncertainty about offspring parentage due to communal breeding.

• Attract predators: Larger groups are more conspicuous and may attract predators.

• Risk of parasites (bird mite, blowfly larvae, Plasmodium, Trypanosoma): Increased susceptibility to diseases and parasites in crowded conditions.

Heritable Basis for Choice of Group Size

• The Browns switched ~2,000 young birds from nests in big colonies to nests in small colonies (& reverse), & discovered that these birds chose the same colony size as that in which they were hatched, indicating a genetic predisposition for group size preference.

• Suggests a genetic difference between birds that choose to live in large groups versus small colonies, highlighting the role of genetics in social behavior.

• They return to where they were born irrespective of where they were raised, emphasizing the influence of natal origin on group size choice.

• They are picking the colonies that their parents picked; so it is not environment, it is genes that appear to be dictating their choice, reinforcing the heritable aspect of group size selection.

Flocking

• An aggregation of large numbers of individuals within a species often outside of the breeding season, forming cohesive groups for various purposes.

• Causes - opposite to circumstance which promotes territoriality, when resources are unstable, driving birds to seek safety in numbers.

Benefits of Flocking

• Reduces the threat of predation:

  • Merlins have better success foraging on shorebirds when flocks are smaller, indicating that larger flocks offer better protection against predators.

Costs of Flocking

• Dominance hierarchy within flocks (Harris Sparrows - dominance indicated by black-markings): Established pecking orders that influence access to resources.

• Increased competition for limited food supplies, increased risk of disease, and increased aggression to maintain individual distances: Negative consequences of crowding and resource scarcity.

• Work by Caraco suggests there should be an optimal, or intermediate, flock size due to trade-offs between: feeding, fighting, scanning for predators, balancing the benefits and drawbacks of flocking.

• Joining a flock theoretically decreases the risk of being caught and eaten, because there is safety in numbers, providing a collective defense against predators.

• Yellow-eyed junco:

  • Average flock size increased from 3.9 to 7.3 juncos when a Harris‘s Hawk regularly flew over the feeding grounds (Caraco et al. 1980), illustrating the adaptive response to predation risk.

Mixed-Species Flocks

• Many tropical birds live almost their entire lives in mixed-species flocks, forming diverse communities with various ecological roles.

• Sympatric flocking species often shared distinctive plumage patterns, suggesting a role for visual signals in flock cohesion.

Advantages of Staying Together in Flocks

• Is it possible that there are local “dialects” of flocking signals? : Investigating the potential for regional variations in communication within flocks.

Hierarchy of Interspecific Dominance Among Birds That Follow Army Ants

• Ocellated antbird (A)

• Bicolored antbird (B)

• Spotted antbird (C)

• White-plumed antbird (C)

• Mixed flocks in temperate regions too: Flocking behavior extends beyond tropical environments.

• The tension between trying to eat while avoiding being eaten is central to avian social behavior, highlighting the fundamental