I. Migration

1. I. Migration • Examples • Lesser Snow Goose • Some fly from James Bay to Gulf Coast, about 2700 km (1700 mi) in less than 60 hours, averaging 50 kph (30 mph) at heights of 3,000 m (10,000 feet [almost 2 miles high]) • Golden Plover • Fly from Nova Scotia to Argentina in 48 hours (4500 km @ 60 mph)

2. A. Examples, continued • Hudsonian Godwit migrates from James Bay to Chile and Argentina (4800 km) non-stop • Young make the same trip 1 month AFTER the adults have migrated

3. B. Questions • Why leave the winter home in the spring? • Why leave the breeding home in mid-summer or early autumn? • Many shorebirds are early migrants • Why winter and summer in different climates? • Yellow-bellied sapsuckers • Some breed in Alaska and winter in Ohio • Some breed in Ohio and winter in Panama

4. B. More Questions • Why fall migrate from long or long-growing days (or when photoperiod is not changing) to short or short or short-growing days? • Why move south when weather is • Getting colder? • Getting warmer? • Remains unchanged? • Be so precise in choosing a winter home? • Bobolink migrates from across northern US to a single mountainside in Bolivia

5. C. Migration Defined • Regular, extensive, seasonal movements between a breeding region and wintering region

6. D. When did migration evolve? • First good flyer was Ichthyornis • Tern-like bird with a keeled sternum • Existed 130 million years ago • Cretaceous period • Order Anseriformes • Ducks, geese, and swans • 65 million years ago (Cretaceous also) • Most modern bird families and genera • 13-25 million years ago (Miocene) • Migration probably began • 2-13 million years ago (Pliocene; pre-ice age) • When was the last ice age? • 14,000 years ago (about)

7. E. How did Migration evolve? • Four main theories • Glaciation Theory • Birds would breed in the north when glaciers receded each spring, then were forced south by ice in autumn • Flaw – ice was as much as a mile thick in places • Evidence – certain “refugia” like this did exist during the last period of glaciation (one centered on Banks Island) that are now important breeding colonies for snow geese and some other arctic breeders • Southern Home Theory • “base of operation” was the wintering home and locality fixation for this home is only abandoned for breeding • Northern Home Theory • “base” is the breeding range, and locality fixation is abandoned due to environmental factors

8. E. 4 theories, continued • Continental Drift Theory • Land masses have been moving north from their antarctic origin • Birds are trying to return to their ancestral homes • Flaw – most would have lost any locality fixation over so many generations • Most evidence points to Southern Home • Fossil records • Ancestral home • always at or south of current wintering range • Roseate spoonbill • U.S. breeding population exterminated, leaving a migratory population that bred in Mexico and wintered in Argentina, but a migratory population has re-established in the U.S. on its own

9. E. 4 theories, continued • All 4 theories assume • Locality fixation • A restlessness exhibited when in unfamiliar surroundings (may or may not be inherited) • Abandoned only when an alternate locality fixation takes over (e.g., due to hormonal changes?) • Powers of orientation and navigation • Today • Locality fixation may be dwindling in some species but still very strong in others • Push north seems more intense • Competitive advantage of getting best territory or nest site, breeding early, ready to leave early

10. F. Ultimate Causes of Migration • Natural Selection • If migrants are (were) better adapted, the trait would persist and win out • Increased fitness • Several reasons why fitness is increased • Food – quantity, quality, relatively unexploited • Territory – 8 X more space liberated in N. hemis. • Day length – longer days for young to feed/be fed • Predators – fewer in north, especially terrestrial • Parasites –fewer in north • “three-pronged natural selection” • Makes migrants more flexible; less chance of extinction • Weather? • Probably not directly

11. G. Inherited or learned? • European Cuckoo • A nest parasite that moves north just long enough to lay eggs • Young know where to migrate once they mature • Herring gulls and some waterfowl • Young migrate before parents • Egg-switching experiment • Eggs from a migrating gull species placed in nest of a non-migratory gull species • When young matured, they migrated correctly • Eggs from non-migrating species placed in migratory species nest • Young migrated with adoptive parents

12. G. Inherited or learned, cont. • Tendency to migrate is evidently learned in some species and inherited in others • Migration tendency appears to be very strong • Genetically • Behaviorally • Evolutionarily

13. H. Proximate factors • Day length • Temperature • Rainfall • Barometric pressure • Wind speed or direction • Food availability

14. I. How precise is timing • Swallows of San Juan – Capistrano arrive the same day each spring? • March 19 • Some seabirds arrive on breeding island within the same week each year • Snow geese arrive at DeSoto NWR as early as August or as late as November • In general, fall timing is less precise • Arctic breeding can be very precise (and must be due to limited snow-free season)

15. J. Migratory Restlessness • Zugunruhe • Observed in caged birds • A few hours each night for several nights • Bird awakens during night and hops and flutters vigorously in its cage for a period of hours until the behavior gradually diminishes • Has compass orientation • Which way depends on season • Associated with fat deposition • Build up prior to migratory journey • Starved birds still exhibit zugunruhe • Associated with gonad development • Only in spring – increasing day length stimulates the anterior pituitary to release gonadotropins • Castrated birds still exhibit MR and fat deposition • MR, Fattening, and gonad development not necessarily physiologically linked in all species

16. K. Zugunruhe Experiments • White-throated sparrows - Meier (1973) GlandHormone Adrenal Corticosterone Anterior Pituitary Prolactin Discovered the timing of peaks of these hormones in the blood changed seasonally: Spring: Peak of prolactin is 12 hours after corticosterone Fall: 6 hours between peaks Otherwise: about 8 hours between

17. 1. Meier experiments, cont. • Controlled photoperiod of 16 light and 8 dark hours • Injected prolactin after natural peak of corticosterone as follows: • Inject afterResponse • 12 hours Fattening, migratory restlessness (MR) to north and gonadal development • 8 hours no response • 4 hours fattening MR to south no gonadal development

18. 2. Other Experiments • Captive bramblings (Europe) and indigo buntings (N. Amer.) • Can bring into MR anytime by controlling photoperiod • Certain captive warblers exhibit MR, fattening, etc. at proper time, regardless of photoperiod • Flown by plane to wintering home, they kept exhibiting MR for the same number of nights • Budget for MR, independent of proximate environmental stimuli • Caged white-throated sparrows exhibited fattening and MR within the same 3-day period for 8 years

19. 2. Other experiments • Some caged birds not allowed to breed keep exhibiting MR into the summer • Breeding may end MR in some species • Observational studies show • Canada geese migrate north with the 2°C isotherm 2) Willow warblers migrate with the 9°C line 3) Gray cheeked thrush doesn’t migrate until its breeding grounds are “ready,” then moves from South America to Canada

20. 2. Other experiments, cont. • At the Wildfowl Trust in Britain, an accidental experiment lends evidence. In response to public interest, they were feeding waterfowl, but since it got dark early, they used floodlights to illuminate the feeding waterfowl. Then they noticed that these birds migrated a full six weeks before the other birds in Britain began their migrations. In subsequent years, they varied the length of time these lights were turned on and found they could alter the time of migration in the waterfowl.

21. L. Navigation and Orientation • Two major theories/hypotheses (1953) • Kramer’s Map-and-compass hypothesis • Map is in the birds head • Uses the sun to navigate • Matthews Sun-arc theory • Bird extrapolates peak of sun’s arc by observing sun’s movement • Compares angle with remembered peak to get latitude • Compares noon azimuth with remembered noon azimuth to get longitude (clock in head) • All works automatically

22. 2. More-recent discoveries • Sun • Clock-shifting pigeons • Pigeon contact lenses • Stars • Indigo bunting research at Cornell • Wild birds could navigate in a planetarium, but birds raised in the lab could not • Birds raised in the planetarium could not either • Young learn to navigate by viewing the rotation of the sky • Landmarks • Yes, but some experiments suggest only within 5 km of their “home”

23. 2. Recent discoveries, cont. • UV light and plane of polarization • This allows birds to see the sun’s location through the clouds, but can they? • Infra-sounds • Low (<20 HZ) frequency sounds • Produced by ocean waves, storms, auroras, volcanoes, reflected off mountain ranges • Used conditioned cardiac response to see if birds could hear these sounds

24. 3. Conditioned Cardiac Response • Measure initial heart rate • Provide a stimulus (e.g., infrasound) • Immediately give an electric shock • Bird increases heart rate with stimulus in anticipation of receiving the shock • But only if it can detect the stimulus • Results for infra sounds • Pigeons heard as low as 2 Hz • One heard down to 1.25 Hz so they tested the others • The others heard at 1.25 and below • Pigeons breath at 2 Hz, masking the sound • They hear down to 0.05 Hz • Limit was due to equipment (don’t know their limit!)

25. 4. More on infra-sounds • Problem: Due to long wavelength, we cannot tell where they are coming from • Doppler frequency shift would allow a flying bird to detect direction • Bird would have to fly 50 mph to increase frequency by 12% • Can they detect a 12% difference? • Use CCR to test • Indeed, pigeons detect as little as a 5% shift • Owls can detect a 1% change! • But do they use these abilities to navigate?

26. 5. Earth’s magnetic fields • Wallraff’s theory (1978) • Birds posses, not a compass, but a magnetic probe, measuring intensities and not direction • Located in median plane of body, not horizontal, but more vertically inclined • Ignores polarity • Function depends of flapping flight • Important parts are in the wings • Function is complicated by winds • Don’t measure absolute intensities, but rates of change in relation to flight direction • Birds must scan and oscillate over long distances to maintain their course

27. 5. Magnetic fields, continued • U.S. Researchers found metallic particles in pigeon neck muscles. • Living cells are affected by electromagnetic fields in a variety of ways • Researchers do not know how molecular-level responses can send navigational messages to the brain • CCR tests originally showed no North American birds could detect magnetic fields

28. 5. Magnetic fields, continued • European researchers in the late 1980’s found their birds could detect magnetic fields • Maybe European species evolved different abilities • We now know that nearly all vertebrates tested to date can detect the earth’s magnetic fields • Including humans!

29. M. Some conclusions • The many bird species that migrate differ in many evolutionary respects • Learned vs. inherited • Precise timing vs. influenced by environment cues and stimuli • Navigation by sun, stars, landmarks, infrasounds, or magnetic fields • All evidence that migration evolved separately in many species and was not inherited from an ancient ancestor • Given the evolutionary advantages to migration, the ease with which birds can travel long distances, and the powers to navigate, potentially by several means, it would be amazing if birds did NOT migrate