Bird Exam 2: Annual Cycles

Birds face times of stress and times of opportunity

• Correspond to changes in day length, climate, and resources (especially food)

  • In tropical areas – wet vs. dry seasons often facilitate ‘changes’

  • extended daylight - opportunity

• Predictable events

  • know when the opportunities are

survival 2 examples

• depends on changes in appearance, physiology, and behavior

• CMWA-SCTA

  • cape may warbler

    • behavior change

    • known for eating caterpillars in the summer

    • arrives in the tropics

      • eats nectar all day all night all summer(but not the summer, the winter) 

      • they eat so much that their tongue is semitubular 

  • scarlet tanager

    • dramatic change in appearance

    • being bright red is not a good idea in the nonbreeding season

the annual cycle

• Adult birds invest more time and energy than required for daily survival for 3 main reasons

  • Reproduction, molt, migration (in some cases)

  • cannot migrate and molt at the same time

    • too much going on, feathers aren’t good enough

• Those demands, combined with season resources and opportunities define the species annual cycle 

permanent resident

• simplest type

  • common pigeon

    • good food, mates?

      • keep breeding

    • no mate, young independent

      • molt

forest birds in borneo

• resident bird

• breeding season is times with the availability for food 

  • rainy season = more food soon

white crowned sparrow

• people have done a lot of research

  • interesting geographic range

  • subspecies with different migratory regions

migration

• more complex

• Major changes in physiology, body composition, behavior

• After breeding and molting

  • Gather in large flocks

  • Eat large amounts of food

    • Doubling body mass with fat stores

    • subcutaneous fat deposits 

• Twice a year 

Annual cycles of WCSP studied in depth

• Driven by a series of specific stages

• Hormonal cues drive stages

• environmental cues tell them when to do stuff

Specific species

WCSP

• Z. I. gambelii: long distance migrant

• Z. I. pugetensis: short distance migrant

• Z. I. nuttalli: non-migrant

• Breeding order: nuttalli – pugetensis – gambelii

  • n

    • already on their breeding ground

  • g

    • has the least amount of time for breeding bc they need to travel the farthest

    • migrating is dangerous

    • extended daylight

    • reduced number of animals in the breeding ground

Annual cycles require the orderly integration of behavior and physiology

• Physiological controls regulate reproduction, molt, sleep, feeding, migration

• Neuroendocrine systems synchronize cellular rhythms

• For migration: a well developed pineal gland (top of brain), with photosensitive cells, monitors light-dark cycles

  • light through the birds skull

• timing is crucial

circadian rhythms

adaptation of cellular organisms to the 24hr clock

photoperiod

• day length

• Helps to trigger molt, migration AND determine optimal breeding time

• Dark-eyed Juncos: 5-10min increase in photoperiod triggered testis growth

• super important for birds

• changes in daylength triggers the amove 

• Juncos

  • past shortest day of year, increase in daylength

  • triggers increase in testi size, just that 10 min increase

breeding seasons

• Guiding the evolution of control systems includes factors associated to timing

  • Food supplies

  • Nest sites

    • for some species it is a greater question for them

    • cavity nesting birds

      • woodpeckers

    • cliff swallows

    • american dippers

      • on the stream, on a rock/bank

  • Location of favorable climate

  • Reduced predation risk

These ‘ultimate’ factors of breeding

• While tuning the control system, provide no guarantee against unforeseen changes

  • Drought, parasites, predation  

• fine tuning components of the breeding season

‘Proximate’ factors are

• the external conditions that actually induce reproduction

  • Temperature, correct habitat, abundant food, displays of aggression among neighbors (counter singing)

    • Help consummate the final stage of gonad and ovarian development

  • Pinyon Jays- 

    • just the site of cone triggers gonad enlargement

  • Red Crossbills- 

    • abundant conifer seeds, start to breed in January (surrounded by snow)

    • just need that food source to start

tropical nesting seasons

• Longer than temperate zones

• 6 – 10 months

• start of the rain season

• Lowland Costa Rica

  • Peak at the end of the dry season

    • Kingfishers are an exception

    • drill mudbank nests

    • fish are more concentrated in the dry season, water is more clear

temperature testing season

• 3 – 4 months

• In the high arctic, only about 1 month is suitable

  • Might speed up the process by using old nests

    • don’t have time to build a new one

  • you are only flying so far

Local populations respond to local conditions

Brown Pelicans- seasonal at northern sites but prolonged at tropical sites

timing of migration

• Precise arrival and departure dates are an impressive feature of migration

  • Broad-winged Hawks

    • 14 day window

    • very precise timing

• Zugunruhe: migratory restlessness

  • Caged migratory passerines predictably become restless just before the time to migrate

• Daily weather patterns influence migration

  • Northwest winds at Hawk Mountain

  • Rain- slows or stops migration

scheduling high cost efforts

• aelf-maintenance – Highest priority

• Social interactions for food or a roost site – Second highest priority

• After that – birds can start to assume costs associated with reproduction, molt, etc.

• Generally, geography related

• Reproduction and molt must be scheduled for when abundant resources are available

Generally, geography related

• Northern areas, with severe winter weather, might only permit self-maintenance

• shore birds

  • if the bay is bad, they might just no reproduce bc their body condition isnt good

Reproduction

• Peak activity = 50% increase in daily energy expenditures

  • Early: courtship, territoriality, nest building

    • fighting is worst in the beginning

    • once they are established, they just check in with neighbors

  • Mid: egg formation incubation 

    • (especially waterfowl)

      • largest among of egg material based on body weight

  • Late: feeding nestlings

molt

• massive undertaking

• Follows breeding and precedes migration

  • Often suspended for migration

• Birds can strategically adjust timing and speed of the molt

• Complete molt is a major undertaking

  • 1000’s of feathers

    • 25-40% of an individual's dry mass (excluding fat and water)

  • Draws significant protein and energy reserves

    • Synthesize feathers and offset cost of poor insulation and flight efficiency

      • so need that energy

  • There is a long list of physiological changes

    • Cardiovascular, keratin in skin, increased iron need

climate change

• we know birds are sensitive to weather

• It shouldn’t take too much imagination to figure out how climate change could impact birds

  • El Nino: periodic warm-water disruption of cold upwelling off the coast of Ecuador and Peru

    • Destroys anchovy industry

    • On a larger scale: the entire equatorial Pacific Ocean receives a major increase in rain 

      • Severe adult mortality on Christmas Island

• tree swallows

  • laying eggs 9 days earlier

• mexican jay

  • laying eggs 10 days earlier

• we don't know how quickly species will be able to respond