Ornithology Quiz 4

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, which makes food resources become available earlier, so many birds migrate earlier to track those conditions.

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.