Migration and navigation 2/3

Question 1

Definitions of migration

Answer 1

‘Specialised behaviour especially evolved for the displacement of the individual in space’ -Dingle (1980).

‘Persistent and straightened-out movement effected by the animal’s own locomotory exertions. It depends on some temporary inhibition of station-keeping responses, but promotes their eventual disinhibition and recurrence’ – Kennedy (1985)

Movement by a substantial proportion of the population to another habitat or biome (or geographical area?), followed by return to the original habitat (usually in a similar geographical location to the starting point). Northcote (1978)

Generally quite synchronised; fitness benefit (adaptive behaviour enhances survival and reproductive output); feeding and mating are usually suppressed during migration

(Not same as colloquial use, or even other scientific uses)

Question 2

Extreme migration - or just wide ranging?

Answer 2

Long-lived animals that between migrations forage in the ocean

Cyclical as seen in Shearwaters

Bonfil et al. 2005: long dist migration in sharks – however return movement not recorded – so could this just be dispersal?

Question 3

Mass migration of ungulates in East Africa

Answer 3

or do they just have a big home range?
Probably migration as it is cyclical and adaptive

It is mass movement that involves most of the population

Movement is cyclical, seasonal and beneficial (for water and food resources)

Appears to fit the definition of migration.

Question 4

Humans have been aware of Animal Migration for millennia

Answer 4

essential for hunter gatherers and still fundamental to existence of Inuit, Lapp peoples; bird migrations written about by Homer and Aristotle

Question 5

Locust swarms can eat upto 3000 tonnes of food per day

Answer 5

From The Bible: [Locusts] ‘covered the face of the whole earth so that the land was darkened, and they did eat every herb of the land and all the fruit of the trees which the hail had left: and there remained not any green thing in the trees, or in the herbs of the field, through all the land of Egypt’

Question 6

Why migrate?

Answer 6

Cons: Migration is physiologically expensive, requires considerable morphological and navigational adaptation, and exposes animals to unfamiliar areas with concomitant risk of predation. Also essential to stock up sufficiently on food before migrating.

Main reasons: Variable environmental conditions in space and time

Migrate to enhance fitness:
–Food
*insectivorous birds escape cold winters (when prey is scarce)

–Climatic conditions
*caribou seek abundant pasture in 24h Arctic growing season
*Arctic migrant birds also take advantage of seasonal glut of food
*wildebeest follow water availability

–Safe birthing grounds
*blue whales to warm waters
No food available as tropical seas have low productivity
But young have a better chance of surviving
*green sea turtles to sheltered sandy beaches (tectonics?)
*penguins to Antarctic mainland (no predators)

Question 7

Dispersal hypothesis for the evolution of migration

Answer 7

Salewski & Bruderer (2007) - conceptual model in a population of birds

( probably more widely applicable to other animals)

1. Individuals in resident population disperse at maturity.
2. Disperse until find vacant breeding territory
3. Some, not all individuals travel to a distant territory to breed
4. If resource abundance declines (e.g. autumn) in distant “outpost” breeding territories, they + offspring will die unless return to natal area. (Selection favours those returning home).
5. Putative migrants benefit further by returning to distant (low competition) breeding territory when conditions improve.
6. = Partial migration – not all of population migrate, residents remain. Over time, adaptation for specialisation of migrants (navigation etc). If selection favours migrant ecotype, over resident, whole population will eventually become migratory

Question 8

Migration trade-offs

Answer 8

Sometimes one of a set of strategies

fitness benefits might be similar

–partial migration
–salmon alternate strategies –resident vs migratory (see Gross 1991)

strategies might depend on early developmental
rates, current condition (epigenetics)

similar fitness benefits might lead to frequency dependence

Question 9

Migration trade-off example: Sock-eye Salmon

Answer 9

In North American Sockeye Salmon Jack phenotype remain small and return to the river after just 6 months whereas Hooknose phenotype stay at sea 18months and grow to be far larger. Jack males sneak and hooknose males fight. Females are nearly always large type to collect more food and allow for best egg production.

Proportion of hooknose reflects relative success of jacks and is usually related to how favourable conditions were in the open sea that year.

Question 10

Northcote’s scheme of functional migration

Answer 10

see diagram in notes

Northcotes model does not always apply.

Often in migratory species:
Refuge = feeding habitat in non-breeding season
Reproductive = feeding habitat in breeding season

Question 11

Feeding migration e.g. locust swarms

Answer 11

*Feeding mass-migration from breeding area to feeding areas (on emergence and development of flight) - but usually one-way (no return, due to short life cycle)

*Stratiform swarms – flat, ground-hugging with high density

*Cumuliform swarms – tall, towering swarms up to 1 km in height, less dense

Question 12

Ontogenic migration

Answer 12

May be

Single cycle between habitats e.g. Pacific salmon, eel, lamprey (semelparous)

Or

cf repeated cycles e.g. Colorado pikeminnow, swallow, Arctic tern (iteroparous)

Question 13

Different types of migration

Answer 13

i) multiple-return

ii) one-return only

iii) single trip

iv) multi-generation migration

v) nomadism

(see diagram in notes)

Question 14

Multiple return migration

Answer 14

–often Seasonal migration

*latitudinal
*longitudinal
*altitudinal

Question 15

Cyclical migration

Answer 15

in long-lived animals, where longevity is greater than the temporal scale of the environmental triggers of migration, migrations are often cyclical, moving between two or more areas of strong inclusive fitness benefit. E.g. Feeding and reproduction in many latitudinal-migrant birds such as barn swallows

Question 16

one-return only

Answer 16

typically species that reproduce and die following return trip e.g. Salmon

Question 17

Single trip/multigenerational migration e.g. monarch butterflies (Danaus plexippus)

Answer 17

Return trip is split over generations

migrate between the plateaus of central Mexico (winter refuging) and US / southern Canada (reproduction, growth)

Autumn migrants (hatched summer) have never overwintered or visited Mexico – use inherited directionality mediated by biological clock and sun compass (Perez et al., 1997)

Spring: reproduce and die on the way north.

(Summer) next generation(s) continues journey north

Heritable trait, sun compass related and relies on the photoreceptors on the ends of the antennae – removing the antennae tips results in random movement and an inability to navigate

Monarch butterfly: migration to overwinter refuges for diapause Antennae have photoreceptors – use a sun compass to migrate that requires intact antennae (Merlin et al. 2009)

Question 18

Nomadism

Answer 18

poorly researched – but see Gibson et al. (2021) for Australian arid-zone birds….

expansion and contraction from core range

or movement following unpredictable resources / conditions

difficult to differentiate from “irruptive” species

e.g. Budgies

Question 19

Intraspecific variation in migration

Answer 19

Local variations in migrations may occur – local adaptations and differences

e.g. Dolly Varden – Savelinus malma (a salmonid fish)
(see diagram in notes)

Migration reduces competition with conspecifics by using resources at different times/locations to others

Question 20

How to measure migration path?

Answer 20

Initial predictions can be based on popular folklore
for example European swallow overwintered in ponds – first and last observations at them either side of winter

Observation of mass movements is possible visually or using radar

Animal marking

-Unique external marks and repeated observation (place, time) -Unique integral marks (e.g. genetic markers) to follow population trends – generally longer term population expansion / contraction; Isotope signature in tissues reflecting habitat characteristics (diet can be tracked this way)

Mass spectrometry of feathers from two bird species shows a difference in Nitrogen isotopes that shows difference in ranges

-Applied coloured/numbered marks, bands, tags, rings – spatial effective but temporally poor
(excessive recapture can alter behaviour)

-Applied telemetry tags – radio tags, acoustic tags, satellite and GPS tags … ICARUS/PULP

-Geolocation from sunset/sunrise, daylength – finer scale but usually only for larger animals

MDNA haplotypes across the breeding range. From this it is possible to observe characteristic stable isotopes

Question 21

How to migrate: passive transport

Answer 21

Many animals can migrate largely passively e.g. eel larvae, aphids by local, directed behaviour

Even large animals can use passive transport

e.g. ‘Selective tidal stream transport’ at sea.
When tide is running in opposite direction to desired travel route, seek refuge (often near bottom).

Question 22

Passive transport example: plaice

Answer 22

e.g. plaice spawning & feeding migrations in North Sea (Arnold & Metcalfe) – Data Storage Tags (record temp. and pressure – pressure tells us the depth)

Time x axis depth on y avis – troughs shows periods spent resting on the bottom (we know the depths across the North Sea bed to identify where plaice are resting)

When tide is running broadly towards direction of travel, swim up into tidal stream – ‘hop on – hop off’!

Question 23

Passive/assisted transport in insects

Answer 23

Few insects are powerful fliers, yet many can travel long distances in coordinated manner, by local, directed behaviour + Planetary Boundary Layer, climb to top of vegetation and take off

Gain height and altitude to use high air circulation currents

Descend partly due to air currents, but partially by vertical flight behaviour

Also, ‘ballooning’ in flightless groups e.g. spiders - which drift using silk

Question 24

Movements above the PBL (place based learning)

Answer 24

insects tend not to move far if they are below PBL, they do if above the PBL;

transported by convection currents avoid geographical obstacles; common in Odonata, Coleoptera, Lepidoptera & Diptera; migration determined by air masses; many species are found at higher levels; tend to move downwind on air currents.

Question 25

Aphid migration

Answer 25

finding new food when resources become poor, then reproducing rapidly to exploit resources

No. flying depends on no. young adults, flight time & weather;

+ve phototaxis takes them up (up to 1220 m);

Fly up to 12 hrs, several km, but exceptionally 1000 km;

When they become tired the physiological response causes –ve phototaxis & attracted to plants.

Question 26

Cues that initiate migration

Answer 26

Mechanisms regulating migratory capacity & behaviour – endocrine influence is important. Developmental processes, e.g. development to ontogenetic stage, achievement of a mimimum size etc

Hormones important in control development of locomotor apparatus, reproductive organs and behaviour

Responses to environmental cues / climatic changes – mediated through day length, changing temperature, precipitation, ice melt, patterns of river flow etc. Mediated via hormone effects

Migratory restlessness is observed in wild and captive animals – Circannual rhythm

Question 27

Biological cues

Answer 27

(see flow diagram in notes)
‘Clock genes’ in SCN turned on & off by the proteins that they encode for feedback loops with 24h cycle. Changes in photoperiods affect hormones

Also peripheral clocks: most cells have timing mechanisms that use many of same clock proteins may function independently of the SCN.

SCN sends rhythmic signals (neuropeptides) to pineal gland (endocrine gland in brain).

Melotonin hormone production controls circadian rhythm in vertebrates.
In humans many other hormones also contribute (see diagram)

Question 28

For more proximal causes and control of migration

Answer 28

see notes