EXAM 2 (LOCK IN)

Breeding systems, migration, conservation

Migration

• Seasonal long-distance movement from one geographic location or habitat to another

Breeding season

Arctic, boreal, temperate areas

Non-breeding season

Temperate, subtropical, tropical areas

Long Distance Migration → Arctic Tem

Travel ~40k km/25k mi per year

Flyways

Migration corridors that generally follow major geographical features such as mountain ranges, rivers, and valleys

Atlantic Flyway

Flyway that follows the Atlantic Coast

Mississippi Flyway

Flyway that follows the Mississippi River

Central Flyway

Flyway that follows the Great Plains

Pacific Flyway

Flyway that follows the Pacific Coast

Tracking Innovation

GPS devices getting smaller and more lightweight, can now be solar powered

Doppler Radar for Tracking

Distinguishes dense flocks of migratory birds, often appearing in reflectivity when filtering out weather

Climate change and spring migration

Many bird species are migrating earlier in response to climate change, but responses vary among taxa and ecologies

Some evidence that resident species are shifting their breeding earlier than migratory species

Pros of living in/migrating to Tropics

• Increased efficiency in thermoregulation

• More dependable, year-round food resources

Cons of living in/migrating to Tropics

• Less land mass = higher density of birds per square area, thus troublesome to claim territory

• Higher predation rates

Pros of living in/migrating to Temperate/Boreal/Arctic

• Long summer days = abundant resources (water, nesting, etc)

• More landmass = more space, less density

• Less predation

Cons of living in/migrating to Temperate/Boreal/Arctic

• Cold winters

• Costly to thermoregulate

• Low food resources

Photoperiod

Length of the day/sunlight

increasing/decreasing → restlessness, eating to excess, fat deposition, and weight increases

Migratory restlessness

innate, anxious behavior migratory birds exhibit before and during migration seasons when caged

Fat deposition

Subcutaneous layer of fat to fuel long-distance flights

• metabolized by enzyme lipase —> free fatty acids and glycerol

Birds lose 0.2-0.9 percent of their body weight per hour of flight; How far individuals can fly is dependent on how much fat they have in reserve

Stopovers

Areas where birds stop their migration to rest and forage to restore fat reserves

• Often high food resources near large areas with low resources

Diurnal migrations

• Birds that employ thermal soaring to take advantage of rising warm air

• Birds that feed on insects while flying

Nocturnal migrations

• more common; more stable/favorable and cooler weather, leading to less heat loss

• Lesser likelihood of predation by hawks, especially smaller birds

Birds that migrate day + night

Anseriformes and shorebirds

True navigation

Birds navigate to specific patches of habitat hundreds or thousands of km away

• Visual landmarks → recognize features like coastlines, rivers, mountains, highways, and railways as reference points

• Sun compass → sun’s position in the sky, together with their internal circadian clock, to determine direction during migration

• Star compass → pattern and position of multiple stars at night to orient themselves and maintain the correct migratory direction

• Geomagnetism → detect Earth’s magnetic field, which acts like a map of horizontal space and helps them navigate

Threats during migration

• Predation

• Run out of fuel and die of exhaustion

• Strikes with buildings, particularly glass

• Land use changes can also affect navigation and disorient birds

• Species-specific responses to changing temperatures for spring migration, x-axis = temp change, y-axis = migratory passage

• In most species, species arrive earlier in warmer years

• Shows the effect size for each species, which is how many days the phenology changes for each degree celsius

• In general, most species’ estimate is within the negative range, indicating significantly earlier arrival with an increase of 1ºC

• Species-specific responses to changing temperatures for Fall migration, x-axis = temp change, y-axis = migratory passage

• Most species are not adjusting their fall migration timing with changing temperatures

• Shows the effect size for each species, which is how many days the phenology changes for each degree Celsius

• Only 3 species are migrating later in the Fall with warmer temperatures

• x-axis = years, and the y-axis shows latitude change, elevation change, and phenology change for Figures 1a, 1b, and 1c, respectively

• Birds are shifting to higher latitudes (a) and elevations (b) for breeding; most species are shifting to earlier return dates (c)

Shift Ratio

• How birds are changing their latitude, elevation, or phenology as compared to how they are expected to change based on the warming rate of the climate

• Observable change/rate of warmth

• Shift of 100% = “perfectly” tracking climate change

• Negative shift ratios = species arriving later with warming climate

• Positive shift ratios = species arriving earlier with warming climate

• Y-axis = shift ratio

• Black = 0

• dashed = perfect tracking

• Average shift ratios are positive but well below 100, with the greatest overall shift seen for breeding phenology

• Majority of birds have a positive sum, mostly b/c breeding phenology was the greatest contributor

• Y-axis = average shift ratio

• X- axis = individual species

• Bars = one species representing shift bar contributions

How does climate change influence birds to migrate sooner?

Climate change causes earlier spring warming, i.e. above-average temperatures, triggering earlier spring migration; some species now breed in higher altitudes or latitudes to find cooler temperatures.

What issues arise for birds if they migrate earlier than intended?

Migrating too early can cause phenological mismatch, where birds arrive before or out of sync with peak food resources or breeding conditions, which can hurt survival and reproduction.

Monogamy

Two parents raising offspring; ~92% of species

Offspring care responsibilities

Nest building, incubation of eggs, nest defense + Feeding, thermoregulating, and defending chicks

Precocial

Chicks that hatch in a relatively advanced physical state

Precocial characteristics

Developed down plumage, open eyes, self-feed, thermoregulate, move

Altricial

Chicks that are relatively immature upon hatch

Altricial characteristics

Unable to open eyes, sparse down feathers, immobile

Altricial birds are born less developed, but have higher rates of growth than precocial

Social monogamy

Social pairs of birds are not sexually exclusive; in practice, they will share traditional monogamous responsibilities but may mate with other birds

EPC male benefits

Increase fitness with little use of resources

• Doesn’t provide parental care to offspring sired through EPCs

• Sperm is easy to produce

• Drawback: Searching for too many EPCs —> divorced b/c poor quality male

Reasons for divorce

Male cannot produce viable offspring

EPC female benefits

Increase fitness by seeking EPCs that will improve offspring quality

• Increased heterozygosity of young; MHC immunocompetence genes

• “Ideal” mates may differ for production of males or females

• Drawback: Male suspects cuckoldry —> reduced parental care

Purple Martin: EPC Copulations

Colonial nesting

• High quality males @ higher cavities

  • Steals EPCs from younger males

• Larger young males = better mate defenders

• Females do NOT seek EPC once w/ high quality male

Negative correlation between male attraction and parental care

Parental-mating trade-off hypothesis

Benefits derived from parental care do not compensate for the costs of losing extra-pair mating opportunities; males prioritize EPC opportunity > parental care

Positive differential allocation hypothesis

Attractive bird reduces its parental effort b/c its mate is willing to compensate; female settles for male’s effort

Polygyny

Males w/ multiple females; 2~ of species

Polygyny → Birds of Paradise

• Males provide no parental care; advertise w/ plumage, displays, and songs

• Females limited by resources, thus try to choose only high quality males

Polygyny → Bowerbirds

Males build bowers (vessels that emphasize display)

Polygyny → Lek displays

Territories where males gather to flaunt themselves

Lek displays: Hot spot model

Male gather in sites most likely to be visited by females

Lek display: Hot shot mode

males gather around experienced/attractive/dominant males

Lek display: Female preference

females prefer to visit large rather than small clusters of males

Polygyny → red-winged blackbirds

Males establish and defend territories that have high water levels and good nest cover to attract females; females females still will obtain EPCs with males outside of their nesting territory

Polyandry

Sex role reversal; Females attract and overtly pair with multiple males

Obligate brood parasites

Reproduce only by laying eggs in the nests of other species

• Don’t incubate

• Don’t build nests

• No biological parental care

Brood parasitic adaptations

• Fast-egg laying

• Egg mimicry

• Begging calls

• Mouth markings

• Instinct to evict other eggs upon birth

• Accelerated development

• Chick mimicry

• Chick aggression

Brood parasitic-host adaptations

• Nest defense

• Nest desertion

• Egg rejection

• Chick rejection

Cooperative breeding

“Helpers” care for young that are not their own

Cooperative breeding indirect benefits

Kin selection: increase their inclusive fitness by aiding genetic relatives, even at the cost to their own reproduction

Cooperative breeding direct benefits

Experience + inheriting territory, especially when there is a lack of resources

Increased production of offspring with helpers; diminishing return beyond 3 helpers

Ecological constraints

Helpers “help” b/c environment lacks suitable habitats, low annual rainfall, high mean temperature, and high climatic variance

Mobbing behavior

A group of prey give alarm calls, complete aerial dives, and make physical contact with the predator

Males that sired EPO in at least one neighboring nest box were more likely to assist in mobbing those nest boxes than those w/o EPO

Males with extra-pair offspring in a nest are more likely to defend that nest against predators

Males w/ an extra-pair offspring are more likely to participate in mobbing in another nest in comparison to birds who do not have an extra-pair offspring

Mobbing intensity of male B and C did not differ significantly whether nest box A males had sired offspring in either one nest box, or both nest boxes. This shows that the B and C males did not reduce their mobbing behavior if there were extra-paternity chicks in their nests.

Major Histocompatibility Complex

Group of highly variable genes that play a central role in the immune system, presenting antigens to T cells, which enables the body to recognize and respond to infections

Graphs A and C show a median close to 0 and in graph B the median is less than 0. This indicates that females that sought extra pair matings had a social mate with more similar MHC-I alleles than you would expect by chance

Although the randomisation test suggests that SP-EPY have lower MHC-I dissimilarity than expected from random mating, there was no overall significant difference in the MHC-I dissimilarity of the three different pair types

If you were to remove the outlier, females often chose an extra pair male with high dissimilarity; however, given the overall data, the dissimilarity was not significant

Anthropogenic extincion

Extinction of species due to human activity

• Hunting

• Habitat changes

• Introduction of species and pathogens

Island species decreasing due to anthropology

Historic extinctions in North America

• “Game birds” suffer large declines due

• Great Auk harvested to extinction in 1840

• Last wild passenger pigeon killed in 1900

Plume hunting

Hunting birds for feathers to be used for hats and accessories

Victorian fly tying

Flies designed for fishing

Pet Trade

Selling birds

Migratory Bird Treaty Act

Drafted in 1906, signed into law in 1918 —> cannot kill, capture, collect nests or eggs or any other byproduct, or export/import birds

why? motivated by the extinction of birds in 1800s

Incidental takes

Violations that occur due to otherwise lawful activities, included in the MBTA

• prosecuted:

  • oil companies

  • wind farms

Measures to avoid incidental take

Companies work with conservation groups to minimize incidental takes of birds b/c companies don’t want to be fined

• Adding objects to power lines to make them more visible

• increase distance between power lines

• Covering waste pits of mining fossil fuels/pollutants

• Covering open pipes

• Flashing switch lights on cell towers

• Slow wind turbines

Arguing against incidental takes

• Law says nothing about “incidental takes”

• Impedes rights of states to regulate land

• Limits industries to improve and develop services

• MBTA only covered activities where birds are directly affected

Impact of MBTA

• Credited for saving millions or billions of birds

• Halted use of feathers in fashion

• Aided in recover of species that were overhunted

• Used

Habitat loss

Rapid destruction of all types of habitats due to agriculture, pasture land, and development–tropical forests particularly, grasslands, wetlands, etc.

Human-related causes of mortality; cats are biggest culprit of killing birds

Relationship between population and diversity

Loss of genetic diversity due to population decline, hindering ability to adapt to selection pressures

Relationship between genetic drift and population

Smaller population leads to greater genetic drift, thus greater loss of alleles

Bird growth potential

• Short generation time → early production life

• Large clutch size

• Multiple clutches per season

Bird growth limitation

• Large generation time —> reproduce later in life

• Smaller clutch size

• Zero or one clutch/year

Annual mortality positive correlates with age-specific fecundity, i.e. if more likely to die sooner, bird is also more likely to produce more offspring

Annual mortality negatively correlates with age of maturity, i.e. if more likely to die sooner, bird is also more likely to be at age of maturity

Age-specific mortality

Birds more likely to die earlier in life

External limitations to growth

Low foraging efficiency, predation, habitat availability, food availability, disease

Relationship between reproduction + survival and population size

Due to carrying capacity, as population size increases, rate of growth decreases and thus reducing survival and reproduction