L19 - Storms and seabirds Flashcards
Where is it windier?
Over the sea, wind speeds are changing. Extreme conditions can have critical impact on fitness and population processes. Know much more about impacts of extreme temps, rainfall etc on animal pops than we do about the impact of extreme winds on the animals that are most exposed to them.
How do storm winds affect seabirds?
At the nest, at sea.
Winds: nesting sites?
Guillemots, razorbills, kittiwakes and shags breed on cliffs/outcrops. Nests can be exposed to high winds & rainfall.
What can max gust speeds be?
134mph
Long term monitoring results?
Shag 104 nests, 11 plots
Kittiwakes 449 nests, 15 plots
Guillemots 828 nests, 6 plots
Razor bills 173, 5 plots
Storm came from the west, so most plots were exposed.
Nest failure results?
Nests on exposed side of island & low down were more likely to fail. Unclear why razorbills were most affected. Storm freq can impact pop growth.
What determines where birds nest?
Not all cliffs are equal: densities of 0 -> 70 nests per m2.
What can predict where 80% of guillemots breeding sites occur?
A simple model - predictor 1: shelter, predictor 2: cliff angle
Why are birds still affected by storms if they breed in sheltered areas?
Winds so strong they even affect sheltered sites. Changes in wind direction mean sites are not always sheltered.
What is the benefit of cliff angle?
Predator avoidance, young need to jump.
Summary?
We can predict where most guillemots nest with only 2 factors. Other aspects will also influence site choice e.g. nesting ledges. Species will differ in their nesting requirements. Storms can cause mortality at the breeding sites, particularly in eggs and young.
How do storm winds affect seabirds at sea?
Seabirds spend most of their lives at sea.
What do storms cause?
Massive seabird wrecks. Emaciation, drown
How are seabirds affected by winter cyclones?
Storms may prevent birds from feeding: increase water turbidity, alter prey behaviour/ aggregation - the washing machine effect. Little auks are 150 grams - can fast for 2 days before they starve. Guillemots are 1100 grams - can fast for 8 days before they starve.
Why don’t seabirds avoid storms?
Cat 4 winds >73 mph. Auks are unlikely to fly in high winds. Little auks stop flying in winds > 35 mph (16m/s), Guillemots stop flying in winds >50 mph (22m/s). Storms can be over 1000km in diameter. Storms can occur in quick succession - avoid one but another could follow
How many cat 4 cyclones per month could a common guillemot experience?
Up to 4
Where do tropical cyclones form and how?
Form over warm tropical oceans, generated by transfer of heat and moisture from the ocean’s surface. (Typically when cold and warm air masses collide).
What can tropical cyclones also cause?
Wrecks/stranding. Do not tend to occur back-to-back. Wrecks tell us that birds cannot always avoid storms.
What are some tropical birds?
Great frigate birds
Where do juvenile and adult frigate stay?
At the colony, which is not totally safe, as some birds killed by falling trees/branches
What has happened in some cases?
Adults that were at sea flew around the cyclone. Birds changed their course when the cyclone eye was 470km from the closest bird & 800km from the 3 others. Impact on birds: the bird closest to the eye died. 2 birds returned to their original foraging zone after the cyclone passed, 1 bird was displaced to Vanuata, 600km away.
How do birds know when a cyclone is coming?
Wind speed - when the cyclone eye was 250km from europa the wind increased to gale conditions (average ground speed >60 km.h-1.)
Infrasound - extreme climatic events, such as cyclones, produce infrasound that can be detected more than 100km away.
Barometric p - cyclone have very low pressures.
What do some birds have to deal with strong wind speeds e.g.?
Adaptations, only occur in really windy enviros. E.g. streaked shearwaters
What is the world’s most active cyclone basin?
Sea of japans borders
How do shearwaters navigate the sea of japan?
They forage through it
How did the shearwaters react?
Birds moved towards the eye in strong southerly winds. And away from the eye in northerly or easterly winds.
