|
Rob Bierregaard's Home Page
|
|
|
I.
Early (and current) questions a.
Do birds hibernate or migrate? b.
Aristotle knew that cranes moved, but thought small
birds hibernated c.
Until 1600s Barnacle Geese in Europe were thought
to arise annually from barnacles. d.
We now know that no birds hibernate, although some
go into torpor at night (hummers and even vultures (see recent paper in Condor).
e.
We still don’t know where all species go—are
tropical birds austral or northern? f.
Routes are still not well known for many species -
male peregrines II.
What is migration? a.
Seasonal/periodical movement between two locations b.
usually annual - summer vs. winter c.
can be seasonal - dry vs. wet d.
usually latitudinal e.
can be altitudinal III.
Do only birds do it? – no: whales, caribou,
monarchs IV.
Contrast nomadic irruptions a.
Red Crossbills – nearctic b.
Ruddy Quail Dove c.
Toucans V.
Patterns a.
Highly varied b.
usually n-s, esp. in New World because
i.
flyways are oriented that way 1.
rivers 2.
mountains 3.
coasts
ii.
summering grounds n. of wintering c.
Old World often e-w, then n-s
i.
Alps
ii.
N. Sea coast
iii.
Mediterranean d.
Tropics to temperate e.
Temperate/arctic to temperate/arctic
i.
Swainson’s Hawks
ii.
Sanderlings (some)
iii.
Terns VI.
Who migrates? a.
5 MMM birds of 187 spp in Europe and Asia b.
5 MMM birds of > 200 spp in N.A. c.
Some S. Hemisphere species go north, but relatively few VII.
Routes can reflect recent distributional changes a.
Northern Wheatears from UK go back and migrate to Africa b.
Colonists to Alaska from Siberia go back and vice versa VIII.
The 64K question - Why migrate? a.
The proximate answer’s easy: daylength shortens
i.
but not all birds migrate
ii.
need suite of other factors
iii.
the ultimate answer is far more complex and one of
the most challenging questions in ornithology
iv.
need to formulate sequence of evolutionary steps
v.
why do some popns migrate and others not 1.
leapfrog migrations 2.
Sanderlings-some winter in NW NA, others Chile
vi.
Evolution 1.
populations gain or lose habit (examples) 2.
polymorphism - European Robin a.
resident pop’s eliminated 3.
individuals in a sp. differ-Juncos a good example a.
males need to get back to breeding grounds-travel intermediate distance b.
females - adults go furthest-avoid competition with others that go
shorter distances c.
young - mortality high on migration, go shortest, especially young males IX.
Feats a.
25,000 km Arctic Terns b.
Lesser Yellowlegs - 3220 kms/6
days c.
radar studies helped figure out small birds’ habits X.
12 MM birds over Cape Cod one night - heading off
for 80-90 hr flight a.
same as human running 4-min miles for 80 hrs b.
burning gas instead of fat - 720,000 mpg c.
once thought hummers couldn’t make it, but calculations were wrong. d.
Wheatears from Greenland cross 2-3000 km of ocean w/ no help from winds e.
Leaving Europe, birds cross1100 km of Mediterranean and then 1600 km
across Sahara XI.
benefits must be substantial because costs very
high a.
energy costs b.
exposure c.
exhaustion d.
predation – “natural” and human e.
50% small landbirds in N.A. don’t return f.
40% N.A. ducks don’t return XII.
what could benefits be? a.
previously couched in neg. terms
i.
avoid starvation
ii.
shortage of nest sites
iii.
competition for food b.
but why not exploit temporary opportunities?
i.
hummers, tanagers, warblers are really Neotropical
birds that move north to the temperate zone to breed
ii.
not common in African tropical birds – deserts in
the way?
iii.
does occur in SE Asia & India XIII.
Fuel – fat a.
2 xs the energy & H20 as carbs b.
fat deposited in adipose tissue, mostly subcutaneous c.
Blackpoll Warblers & hummers double their weight d.
refueling necessary for long-distance migrants
i.
strategic sites essential for conservation (Map) XIV.
Flight ranges a.
birds loose about .9% body weight/hr (my losing 1.8 lbs/hour)
calculations depend on fat load, head/tail winds, water loss or balance b.
small birds 2,500 km in 100 hrs w/ 40% fat build-up (unless headwinds) c.
Dunlin 3-4,000 km d.
small birds from US northeast will backtrack to land if they meet
headwinds e.
coast on tailwinds- i.e. groundspeed doesn’t speed up with a following
wind XV.
Timing a.
accuracy well known
i.
swallows at Capistrano
ii.
raptors b.
internal rhythms
i.
zugunruhe
ii.
hormones & daylength but not well understood
lengthening daylength in winter stimulate 1.
zugunruhe 2.
hyperphagia 3.
adipose tissue deposition 4.
shortening day in summer triggers: 5.
photorefractory period in gonads 6.
pre-basic molt 7.
hyperphagia & adipose tissue deposition 8.
sex hormones not directly involved, castrated birds follow the typical
pattern c.
weather
i.
American Robins & Can.Geese follow spring thaw 1.
Fronts 2.
fall migration favored after low pressure system passes 3.
spring in front of a high pressure system differs for sexes (sometimes) a.
Ospreys b.
Red-winged Blackbirds XVI.
night or day? a.
raptors & soaring birds & swallows by day –
i.
thermals or feed on the wing b.
small birds at night
i.
less predation
ii.
more favorable flight conditions 1.
nocturnal air less turbulent 2.
lower temperatures reduce heat loss and water retention 3.
refuel by day XVII.
altitude? a.
700-800 m most small birds b.
can be as high as 7,000 m XVIII.
Gauthreaux’s radar studies a.
1940s birds showed up in radar in UK during war b.
1957 US set up WSR-57 radar to track weather - 2” beam c.
Modernizing in early 90s with WSR-88D doppler radar
i.
1” beam - higher resolution
ii.
more powerful - increased range
iii.
doppler - direction & speed!
iv.
calibrate with observations across moon
v.
demonstrates 1.
declines 50% from 65-67 vs. 87-89 2.
habitat preferences/priorities for conservation 3.
roost areas (non-migratory) 4.
important for bird strikes at airports
Study of American Redstarts
XIX.
Navigation a.
need?
i.
find nests
ii.
find food sources far from nest 1.
nectarivores/frugivores 2.
colonial nesters
iii.
find, and return from, wintering grounds
iv.
get home after accidental displacement
v.
storms
vi.
ornithologists 1.
Manx Shearwater 2.
White-crowned Sparrows moved from San Jose b.
how do they do it?
i.
various senses 1.
system of fall-backs 2.
easiest first, then next, etc 3.
Visual landmarks 4.
solar compass 5.
stellar compass 6.
sense of smell a.
petrels - good evidence b.
pigeons - conflicting evidence 7.
geomagnetism
ii.
elements of learning
iii.
genetic component
iv.
the map component 1.
magnetic field? 2.
solar cues - depends on very accurate internal clock c.
experiments
i.
opaque glasses
ii.
release birds on cloudy vs sunny days also clock
shift
iii.
raise birds in planetaria - osprey story on radar
tower
iv.
translocate birds to novel places
v.
"smellectomy" - petrels find their own nesting
material
vi.
magnetic helmets - and magnetic field in metal
cages
vii.
displace young and adults - adults found wintering
grounds, young just went by direction
viii.
hybrids between populations with different
migratory habits have intermediate behavior REVIEW QUESTIONS Is migration just a matter of head south in the fall and back north in the spring? Explain. What evidence supports the use of visual landmarks? Use of the sun as a compass requires what additional knowledge? Describe an experiment in which the use of a sun compass was established. What evidence supports the conclusion that birds use geomagnetism for orientation? Do birds use olfaction for navigation? For orientation? Give examples. What evidence suggests that birds learn how to navigate? If a young bird were exposed to a stationary sky in a planetarium, would it later be able to navigate by the stars? Is accurate compass orientation alone sufficient for migrating to wintering territories? Explain. What internal cues control migratory behavior? What evidence supports a genetic component to the internal control of migratory behavior? How does the quality of winter territory affect reproductive success? How is true navigation different from "clock and compass" orientation? Which do 1st year migrants use? Adults? What do we mean by "connectivity" when discussing bird migration? How can this be studied? Distinguish between ultimate and proximate causes of migration. Do all members of a local population migrate together? To the same places? At the same time? Why or why not? VOCABULARY:
|
