Migration and navigation Flashcards
Migration definition
regular long-distance movements each year to track changes in resources and habitats
Diversity in long distance movements:
* Annual – same indivs return eg. humpback whale
* One migration per lifetime eg. anadromous (migrate up rivers from sea to spawn) salmon
* Multi-generational eg. Painted lady- 60 degrees latitudinal shift in six generations
What is not migration:
- Philopatry: Returning home (eg. of turtles returning to beach where born 35 yrs later can influence migratory patterns
- Nomadism: move widely in search of food and settle + breed where it is locally abundant (e.g. herd o horses)
- Dispersal: movement to escape competition + inbreeding risk
Why migrate
Often occurs when resources/ predators are heterogeneously but predictably disitrbuted in time and space
a) Track resources
b) Evade predators / disease
c) Find suitable breeding sites/ nesting location
d) population regulation -> immuno compromised/ week individuals don’t migrate or die along the way
d) In multigenerational insects …
- Escape conditions incompatible w/ development
- Escape high density
- Reproductive bet-hedging??? Spread repro over many latitudes
Population patterns of migration
1) Leapfrog migration – N. breeding pop’ns winter further south than S. breeding pop’ns (robin)
-> flying over suitable habitat?
2) Chain migration - N. pop’ns replace southern ones = shift south (bald eagle)
-> leaving suitable habitat?
-> Common swift due to Bergman’s principle
3) Telescopic migration – must migrate different magnitudes to reach same common wintering ground (ealanors falcon)
Pattern drivers:
- cost of migration
- competition between individuals
- Bergman’s principle = same species at higher latitudes have larger body sizes for heat conservation (e.g. common swift in northern range are larger-> chain migration as smaller pushed further south)
- availiability of food/ nesting sites/ climate at the locations
Partial migration
Proportion of pop’n that migrate depends on winter vs summer site resource differences and the resource requirment of individuals
-> More individuals migrate at end of sumer if summer sites are poor and winter sites are good
Example: chiffchaffs = facultative migrators (some migrate, others stay)
Example: Tropical king birds – only adult males migrate and only if heavy (want resources)
Example: all arctic turn migrate and tolerate long migratory distance due to difference in resources (prey and light)
Ecological impact of migraton
Disease:
- increase the spread zoonoses / diseases
- Escape disease
- Reduce immunocompetence due to inability to migrate/ die on the way
- Implications for human disease management
Example: fruit batt migration -> Ebola outbreak -> migration may be changed by deforestation, will this affect human health
Example: water foal and avian influenza
Nutrients cycling:
- movement and death of migratory is important for nutrient cycling
Example: 6,000 wildabeast die during migration
- downstream nutrients increase up to 40km away
Example: migratory fish cycle nutrietns between sea water and fresh water (gain most body mass when in sea)
- cycling effects wildflower development, the productivity of salmon berry bushes, the territory size of Pacific wrens
conservation
- undertanding migration helps to focus conservation efforts on breeding or wintering grounds
Example: Wilson warblers
- Not all populations in decline
- Distinct populations in winter site not summer sites so aim conservation on winter sites.
Example: Breeding success of puffin correlated with migration trajectory (using geolocators)
- decreased success if colony big, long migratory distance, higher latitude of over wintering site
- increased colony size, increases migration distance
mechanisms underpining migration
**Timing of migration: **
1) Use sensory cues eg. house marten arrival in oxford depends on Africa temp and departure depends on Oxford temp (summer in Europe + winter in sub-Saharan Africa)
2) Endogenous circannual rhythms – not impacted by photoperiods eg. willow warblers shows zugunruhe in spring + autumn when should be migrating even if kept in dark cage (lab experiment)
**Long distance mechanisms: **
1) Assimilation and regrowth
Example:
- Bar tailed godwits pop’ns migrate 9,000km non-stop flights (Russia to W Africa)
- assimilate gizzard, liver, kidneys, guts during long flights for energy – makes room for muscle + fat
(may even start assimilating flight muscles near end)
- organs regrown at stop over sites to allow feeding
2) Thermoregulatoin
Example: lowered body temperature is an important mechanism of energy conservation in migrating brent geese
2) Long wings
Examples:
- longer wings in migratory warbler species
- 2.7% longer for each additional 1,000 km migratory distance
- Evolutionary flexible -> rapid switches between migratory phenotypes and sedentary phenotypes in Whistling warblers
**Navigation **
- Using the sun/ starts/ moon
- Magnetic sensitivity
- Odour/ environment ques
- landmarks
Inheritance of migration
1) genetic inheritance
- migratory route is genetically inherited
Example
- Black caps SW and SE migrating pop’ns from central Europe (avoid S as then cross large Mediterranean)
- When bread in captivity and put into emlem tunnel during wrestlessness they scrape the side that they migrate.
- can select for those that do / don’t migrate and produce migrant + non-migrants
- Change in migratory pattern-> Now NW pop’n migrating to UK / Ireland for winter
- This pop’n maintained by assortative mating via phenology (the arrive to breeding grounds earlier so mate before other pop’ns arrive)
2) learning and cultural transmission
Cultural example: Big horn sheep
- indivs translocated to new area
- More migratory as yrs after translocation increase as knowledge of env passed down through yrs needed to maximally exploit env
- Better at surfing (correlating movement w/ seasonal shifting peak in forage quality) as yrs since translocation increase
- Over time sheep learn + socially transmit how to green wave surf but slow process
Learning example: white storks following conspecifics to learn route
- breed Europe + overwinter Sub-Saharan Africa
- juveniles = migrate slower, flap more, preen less when land, less successful foragers to take longer to find food
- can’t keep up w/ one adult group so don’t follow same flock for whole migration, but join subsequent groups
- conservation concern – if pop’ns scarcer then harder to find subsequent groups to follow
3) Exploration and refinement
- Birds more similar migration patterns to themselves than others
- Innate program to explore in early years then refine in later years
Example: Atlantic Puffin
- Tracked in two consecutive breeding seasons -> different patterns but both repeat
Methods to study migration
- Radar – eg. painted ladies from N. Africa to Artic circle take 6 generations
- Colour ringing – tropical kingbirds – catch and ring then can identify indivs w/out recatching
- Genetic analyses – blood + feather samples of Wilson’s warbler and SNPS analyse w/ next gen sequencing – showed origin of wintering pop’ns (different species, same overwintering ground differential decline in pop’n so maybe focus conservation on breeding grounds)
- Geolocators – eg. puffins (daylength = latitude, dawn / dusk / midday time = longitude for light sensory, also 2 pins that conduct in saltwater shows bird behaviour + when in sea)
- Lab experiments – willow warblers in cage – endogenous circannual rhythms (using Emlen funnel + zugunruhe)
- Emlen funnel – ink in bottom, paper on sides eg. blackcaps F1 hybrids show S. zugunruhe (shows genetical control of migration orientation)
- Selective breeding - Blackcaps inherit migration – can select for those that do / don’t migrate and produce migrant + non-migrants
- GPS/ARGOS satellite tracking – big horn sheep and white storks
Overview
why migrate
- predators/ food/ disease
- nesting sites
- weather
- Population regulation
Ecological impact
- disease
- nutrients
- conservation
Mechanisms
- Navigation
- Long distance flight
- timing
inheritance
- genetic
- culture/ learning
- individual
