Avian Bio Exam 2

How do bird wings produce lift?

• A bird’s wing is shaped to be bent

• Cambered wing

• More lift is generated with higher air speed

Cambered wing

Causes air to move faster on the top of the wing than the bottom of the wing

Induced drag

• A cost of lift. Happenes when there are pressure differences in the upper and lower surfaces of the wing.

  • Can be reduced with wide spaces in outer primaries

  • Reduced with pointier wings

  • Strongest at slow speed

Alula feathers

• Reduce drag. Direct the air to follow the wing more closely, leading to less turbulence.

Profile drag

• The drag produced by the profile of the bird as it moves through the air (the bird “displacing” the air)

  • Increases with air speed

How ro reduce profile drag?

• Bird’s aerodynamic shape and tail

• Long and narrow wings

Minimum power speed

The bird is able to stay in the air long, but not maintain a high speed

Maximum range speed

• Gives the fastest range with the least energetic cost

What forces affect a bird in flight?

• Upward flight: Lift, offset by weight of bird and gravity

• Downwards flight: Drag, offset by wind+ updrafts, wing flapping

How can a bird offset the downward forces it experiences in flight?

• Downwards flight: Drag, offset by wind+ updrafts, wing flapping

What external forces can birds use for flight?

• Thermal soaring- rising in warm air

• Slope soaring- rising in mountain updrafts

• Dynamic soaring- Flying into a strengthening wind and with a weakening wind

Flapping flight

Requires enough power per body mass of a birds to maintain flight. Eventually birds that are too big do not have enough power to paintain flight (power decreases as body mass increases

Explain the Power/Velocity plot

• Larger species have limited power, which changes the flight style of the bird

  • Hummingbirds have a small body size, and can produce lots of power (more than needed) for hovering 

  • Rock pigeons are larger, and can hover briefly

  • Vultures need to run to get enough power needed to fly

  • The condor needs wind and thermal currents to be able to fly

Why do some birds fly in formations?

• The bird flying in front provides upward turbulence to the birds behind

Intermittent flight

• Flapping phases are interrupted by pauses between each

• May include:

  • Bounding- wings folded next to body (small to medium birds)

  • Gliding- wings stretched out (medium to large birds)

Wing loading

The bird’s body mass per wing area (higher loads require fast speeds & manaeuverability)

Aspect ratio

The wingspan squared divided by the wing area (high aspect ratio (often) = pointy wings)

What different types and subtypes of movement do you know?

• Local movements

• Residence

• Dispersal (natal dispersal + breeding dispersal)

• Philopatry

• Migration (facultative, obligate, partial)

• Nomadism

• Irruption

Local movements

Short trips (e.g. for foraging)

Residence

Same location all year

Dispersal

Movement between breeding sites

Natal dispersal

• Moving from hatch site to first breeding site

Breeding dispersal

• Moving to a new breeding site in the next breeding season

Philopatry

Returning to the same location for several years

Migration

• Seasonal movements between breeding and wintering sites across latitudes or altitudes.

Facultative migration

• migration pattern and timing changes according to the environment

Obligate migration

Migration that follows the same pattern and time every year

Partial migration

A species that includes individuals that migrate and those that don’t (residents)

Nomadism

• Irregular movements to breed where resources are best

Irruption

• Birds that occasionally move in large numbers beyond their migration range in response to poor food supplies (facultative and nomad)

Why do birds migrate?

• To get seasonal resources elsewhere

• To avoid harsh conditions (low food, light, cold)

• Fewer parasites & diseases (in winter areas)

• Benefits of resources outweigh csts of migration

Loop migration

• A species that takes a different route north and south

Leapfrog migration

North species breed north, and south species breed south

What migration strategies do birds use?

• Long-distance migrant: Magnolia warbler, American Redstart

• Loop migrant: Blackpoll warbler

• Leapfrog migrant: Fox sparrow

Broad front migration

• A pattern in which the migrating individuals of a species are spread across a wide area rather than narrower flyways.

Soaring migration

• Use thermals to soar during the day (avoid water)

Hop

• Short bouts of migration and fueling stops (fly at night, rest during day)

Skip

Long flights with long refuling periods (large unsuitable habitats)

Jump

• Very long non-stop flight (requires lots of feeding prior) (Bar-tailed godwit)

What makes shorebirds vulnerable during migration, and what are threats to them?

• Shore birds rely on a few high-quality sites (it effects their survival, thus needs conservation)

• Threats of shore birds:

  • Harbors & airports

  • Shrimp ponds and aquaculture

  • Oil spils

  • Climate change

  • Hunting disturbance

How can we study bird migration? What are some advantages and disadvantages of the different methods to study bird migration?

• Banding

• Visual counters

• Geolocatiors: Log daylight & require recapture (covered nests may fool lights)

• GPS loggers/ satellite trackers for large birds

• Feather isotopes: Shows where a feather was grown

• Genetic information: origins of migrants

• Experiments: Displacement & manipulation

• Radars

How do birds chose when to migrate and at what altitude?

Tradewinds

Tradewinds

Wind changes direction at cerain altitudes and at cerain times of the year

Weather radars

• Can be calibrated with specialized bird radars & sophisticated computer software can be used to track bird migration at a continent-wide scale

  • Uses: Shows weather influences, monitored in real time, migration forecasts

What cues may birds use for orientation and how do they use them?

• Annual cycles

• Magnetic perception

• Solar orientation

• Celestial navigation

• Odor

• Infrasound

• Landmarks

• Learned & innate orientation

Magnetic preception

• Birds have a pigment cryptochrome in their eye that may allow them to see magnetic inclination in presence of blue light

  • Shows north south poles, and east and west

What experiments help to study bird migration and the use of specific cues?

• Adjusting perception of light

• Changing stars visible (solarium)

• Magnet on birds- to upset magnetic orientation

• Displacement 

• Emlen funnel experiments

Migratory divide

Locations where two populations of the same species with different migratory orientations meet and potentially interbreed.

What information would you need to collect in a specific case to show that a migratory divide contributes to speciation?

• The origin of the birds

• Migratory routes

• Hybrids with intermediate migratory behavior

• Selection against hybrids

Ecology

• The study of interactions of organisms with each other and the environment

Abiotic factors

• Physical features of the environment (e.g. temp., topography, rainfall, altitude)

Biotic factors

• Features of the environment that result from other living organisms (cometition, predation, food)

Population

Individuals of the same species living in the same area at the same time

Density-independent factors

• Stuff outside that may affect individuals despite their density (no benefit to certain densities e.g. natural disasters)

Density-dependent factors

•  There are costs/ benefits to having certain densities (e.g. parasitism/food availability)

Calculating pop. size changes

• Birth - Death + Immigration - Immigration

Influences on pop. Size

• Mortality

• Sex ratio

• Competition

• Predation

• Food 

• Weather

• Brood parasites

• Pathogens

• Nest site availability

Trade-offs

Two directions: one in which they produce many offspring and have low survivorship, and the other in which they produce few offspring and have high survivorship

R selection

• many offspring and low survivorship (small birds)

K selection

• few offspring and high survivorship (large birds)

  • More susceptible to mort

Density dependent regulation

• As the density in a population increases, the amount of offspring they produce (fecundity) decreases. If there is a very low density, offspring production also decreases.

Allee effect

• - a tendency for populations at low density to have poorer, rather than better, reproductive success (falls below a threshold level)

Causes of allee effect

• Difficulty finding mates

• Lack of group protection from predators

• Lack of group cooperation

• Inbreeding

• Uneven sex ratios

What are your take-aways from the discussion of the journal article by Rodenhouse et al.?

• Ways to regulate population size:

  • Interactions among individuals (crowding, territoriality)

  • Environmental heterogeneity (variation in environment)

  • Intrinsic differences among individuals

• Methods

  • Warbler density was manipulated- One group of territories were left alone, and in a few random territories all conspecifics were removed

• As population size grows, most birds choose to go to the best sites. Once these sites are filles, warblers will have to settle for lesser quality sites (could be lesser quality due to crowding)

Community

• Interacting organisms of different species

Assemblage

• A particular subset of a community

Ecosystem

• Biological community plus physical environment

Niche

Biotic & abiotic factors that allow a species to occuR

Fundamental niche

• Possible niche based on environmental factors

Generalists

• Species with broad niche breadth

Realized niche

Niche that is actually occupied by a specieS

Specialists

• Species with narrow niche breadth

Density inflation

• an increase in population size when limiting factors (such as competitors or predators) are removed

Character displacement

when species evolve differences to reduce competition when they coexist, leading to greater specialization.

Density compensation

• when some species become more abundant to compensate for the loss of others, maintaining overall population density.

Ecological release

• when a species expands its niche due to reduced competition, often using a wider range of resources or habitats.

Species diversity

• Number of a species

Species richness

• includes both species richness and species evenness (the relative abundance of each species)

What hypotheses explain the high species richness in the tropics?

• Higher speciation

• Lower extinction rates

• Complex habitat structure & less seasonal

What are problematic causes of mortality for birds of prey?

• Eating poisoned rodents → Don’t use rodenticides

• Lead poisoning from eating lead bullets ​​ → Don’t use lead bullets

• Mercury poisoning from eating fish  → Don’t use/release mercury from factories

• Electrocution from power lines → Good construction

• Death from wind farms → Better placement of turbines

• Car collisions → no food scraps on roadsides

What are major causes of the Anthropocene mass extinction?

• Habitat modification, fragmentation, destruction

• Overexploitation

• Invasive species

• Pollution

• Climate change

What are examples of human caused extinctions of birds?

• Dodo- Over hunting

• Great Auk- Over hunting

• Guam rail and Guam kingfisher- Invasive species introduction

Why are island species particularly vulnerable, and what are some of their main threats?

• Sometimes not able to fly away from predators

• Habitat loss 

• Inbreeding → decreased genetic variation

• Not as disease resistant

• What was the likely most abundant bird species to have ever lived, and why did it go extinct?

• Passenger pigeon- Overhunting/ destroyed habitat