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CHAPTER 4
Avian mobility
Avian dispersal
Definition of dispersal
• ‘dispersal’ refers to movements that, at the population level,
have no fixed direction or distance; result in a mixing of individuals
from different localities, but do not necessarily bring about any
change in overall distribution
• ‘migration’ refers to movements in restricted directions for more
or less fixed distances that produce regular seasonal shifts in the
centre of gravity of a population
• dispersal can lead to range extension and colonization and can
have important genetic consequences (i.e. reducing inbreeding,
promoting gene exchange, affecting rates at which populations can
differentiate)
Avian dispersal
Definition of dispersal
• ‘natal dispersal’: measured by the linear distances between natal
and first breeding sites
• ‘breeding dispersal’: measured by the distances between the
breeding sites of successive years
• ‘non-breeding dispersal’: measured by the distances between the
wintering sites of successive years
• natal dispersal generally involves much larger distances than the
other types
Avian dispersal
Definition of dispersal
• species generally form pairs on breeding areas, hence natal and
breeding dispersal affect the genetic structure of populations
• some species of migratory waterfowl form pairs on winter
quarters with males accompanying females back to their chosen
breeding area, thereby adding additional component to gene flow
• degree of site fidelity (philopatry) differs between species and
sexes; female birds generally disperse further than males
• studies on dispersal distances are heavily biased by sizes of study
areas or anthropogenic effects
• rare and mostly undetected long-distance migrants contribute
most to gene flow and colonization events
Avian dispersal
Definition of dispersal
• species-specific dispersal patterns are outcome of evolutionary
cost-benefit balances
• benefits of side fidelity: local knowledge, competitive advantage
due to prior ownership, local adaptation
• benefits of dispersal: movement to better quality habitat,
occupation of successional or patchy/ephemeral habitat, reduction
of inbreeding
• costs of dispersal: failing to find suitable habitat, risk of mortality,
maladaptation
Avian dispersal
Natal dispersal
• in most species, natal dispersal does not show directional
preference, but recoveries tend to decline progressively with
increasing distance (at different scales), both in resident and
migrant species
Avian dispersal
Location of Eurasian
sparrowhawks ringed
as chicks and
recovered in a later
breeding season, in
relation to hatch site
(centre)
Avian dispersal
Natal dispersal patterns of several species ringed as chicks
and recovered in a later breeding season
Avian dispersal
Natal dispersal
• to solve scale problem in comparisons, dispersal distances are
often expressed in number of territories transversed rather than in
metric distances.
• larger species tend to disperse further than smaller species, and
female birds further than males (passerines, owls, raptors, waders,
colonial seabirds)
• within any one population, dispersal distances of both sexes may
overlap greatly
Avian dispersal
Natal dispersal
• in group-living birds (e.g. co-operative breeders), young remain
with their parents on the natal territory for up to several years
before dispersing (Florida Scrub Jay, Acorn Woodpecker, Arabian
Babbler, Siberian Jay)
Avian dispersal
Natal dispersal
• delayed dispersal may develop when all suitable habitat is
occupied by territorial groups (experimental evidence in Seychelles
Warbler)
• young males may inherit paternal territory or take over
neighbouring one, while young females mostly move to another
territory
Avian dispersal
Natal dispersal
• in northern waterfowl males move furthest; since migrant duck
often change mate every year, they may also change their
breeding sites, ensuring genetic mixing
• Geese and Swan keep the same mates for several years and
show higher site fidelity, causing well-marked subspecific
differentiation in these species
Avian dispersal
Natal dispersal
• in shorebirds that show “sex-role reversal” (e.g. Phalaropes),
males also tend to disperse furthest
Avian dispersal
Natal dispersal
• several types of evidence for effects of competition (for
territories, food, nest sites, mates …) on dispersal distances
• (i) fledglings tend to disperse further from their natal sites in
years of higher population density (e.g. European greenfinch)
• (ii) fledglings tend to disperse further in years of low food-supply
(e.g. Coal tit); especially evident in owl species that feed on voles
(Tengmalm’s owl, Tawny owl, Ural owl) where natal dispersal
distances roughly vary in three-year periodicity
• (iii) experimental provision of food reduced dispersal distances in
Song sparrows
Avian dispersal
Natal dispersal
• (iv) late-fledging young disperse further than early fledgers (e.g.
Tree sparrows)
• conclusion: dispersal distances are density-dependent and range
expansions most likely occur with the build-up of population
pressure within existing ranges
Avian dispersal
Breeding dispersal
• birds that have previously bred in an area tend to stay there, or
return to breed year after year
• in many species of seabirds and raptors, individuals often return
to exactly the same sites
Avian dispersal
Percentage of adults in migratory bird populations that
returned to the same breeding (upper) or wintering
(lower) sites in successive years
Avian dispersal
Proportion of adult Peregrine falcons that were present at
nests in the same study areas in successive years
Avian dispersal
Breeding dispersal
• within species, mean adult breeding dispersal distances are
typically about one-half of natal distances, but often much smaller
Relationships between the geometric means of the natal and
breeding dispersal distances of various bird species
Avian dispersal
Breeding dispersal
• (i) higher site fidelity in males
• (ii) higher site fidelity at later age
• (iii) greater tendency to change territorities after breeding failure
• (iv) tendency to move to better territories through early life
• (v) change in territory often associated with change of mate
Avian dispersal
Breeding dispersal
• patterns may be partly interdependent, as young birds are more
likely to obtain poor territories and fail in their breeding
• territory shifts can either be voluntarily or forced by dominant
individuals; may result in mixing of individuals hatched in different
localities and, hence, in gene flow
• multiple broods may involve different partners at close locations
(e.g. House sparrow); other species may nest in widely separated
localities within single breeding season, i.e. due to sporadic foodsupplies (e.g. Eurasian bullfinch, Common redpoll, Eurasian siskin)
or because they stop and breed at two or more point on migration
route (e.g. +400 km for Eurasian dotterel)
Avian dispersal
Long-distance dispersal
• when species depend on unpredictable habitat or food supplies,
year-to-year homing behaviour is not expected (e.g. spring snow
conditions in tundra-nesting species, fluctuating water levels in
shorebirds, irregular rainfall patterns in desert species, tree-seed
masts in boreal finches, rodent densities in predatory species)
Avian dispersal
Annual variation in
breeding distribution
of Great grey owl in
Finland
Avian dispersal
Long-distance dispersal
• speed with which local numbers respond suggest largely nomadic
ranging behaviour (e.g. Northern Pintail occupying shallow and
emphemeral wetlands)
Avian dispersal
Nomadic ranging
behaviour of
Northern pintails
Avian dispersal
Long-distance dispersal
• opportunistic behaviour of dabbling ducks reflected in long natal
and breeding dispersal and low site (and mate) fidelity
Sex and age differences in the percentage return rates of waterfowl
to particular study areas in successive breeding seasons
Avian dispersal
Long-distance dispersal
• among rodent-eaters, most information is available on
Tengmalm’s owls breeding in nestboxes
• long movements mainly observed in females, not in males
• greater residency has been attributed to need to guard cavity
nest sites which are scarce in coniferous habitat while smaller size
allows them to survive on small birds
Avian dispersal
Movements of individual adult Tengmalm’s owls
between nesting sites in different years
Avian dispersal
Long-distance dispersal
• extraordinarily long natal and breeding dispersal distances
recorded from Common Crossbills in western Eurasia, where main
food plant is Norway Spruce (strong spatial variation in seed mast)
• yearly make one major movement in June-August (sometimes >
2000 km)
• in Pine areas, individuals show much higher site fidelity
Avian dispersal
Movements of individual Common crossbills between
presumed natal and breeding sites (dashed lines) and
between presumed breeding sites of different years
(continuous lines)
Avian dispersal
Non-breeding dispersal
• in migrating to wintering areas, young birds do not have the
benefits of prior experience as adults do
• young of Swans, Geese and Cranes accompany parents on first
autumn migration; may maintain integrity of particular breeding
populations
Avian dispersal
Avian dispersal
Non-breeding dispersal
• in most species, young may migrate earlier or later, producing
much more scatter in the wintering sites (but not in breeding sites)
• although less substantiated with data, site fidelity in wintering
sites shows same pattern as in breeding season (e.g. European
greenfinch, Common bullfinch, Ruddy turnstone)
Avian dispersal
Annual return rates of migrant birds to specific study areas in successive winters
Avian dispersal
Non-breeding dispersal
• some individuals of migratory species may hold territories in
wintering quarters (e.g. Black redstarts in Spain)
• significant higher proportion of territorial than non-territorial
birds observed during consecutive winters in same study area
• non-territorial individuals may suffer greater mortality or may
move elsewhere
• apart from differential survival and site fidelity, variation in
duration of stay in particular area may affect chance of resighting
Avian dispersal
Non-breeding dispersal
• some long-lived species (Grey heron, Black kite, Herring gull,
Eurasian oystercatcher) do not breed until several years old
• often show progressive changes to shorter moves or shorter
periods away from the breeding areas with increasing age
• while sex differences in winter site fidelity are apparent in some
species, they are absent in others
Avian dispersal
Genetic research and dispersal
• genetic studies may give additional insight into past dispersal
events that influenced present population structure
• usually compare relatedness within and among populations ,
using measures of DNA structure
• mitochondrial DNA often been used for this purpose, but nuclear
microsatellites and minisatellites evolve (mutate) more rapidly, so
generally show more variation between subpopulations
• comparisons can yield estimates of degree of genetic
differentiation between populations that can be used to assess
rates of gene flow
Avian dispersal
Genetic research and dispersal
NG
CH
MB
Avian dispersal
Genetic research and dispersal
Avian dispersal
Genetic research and dispersal
• effects of dispersal distances on genetic structure of populations
also evident in North American jays of genus Aphelocoma
Avian dispersal
Genetic research and dispersal
• pair-breeding species (A. californica): dispersal over long
distances (> 50 km)
• co-operative group-breeding species (A. ultramarine, A.
coerulescens): dispersal over very short distances (mostly < 2 km)
• in both types, genetic differences between pops increase with
distance, but rate of genetic change per unit distance 3 times
larger in group-breeding species
• faster rate of molecular differentiation may translate to higher
speciation rates
Avian dispersal
Callens et al. 2011, Mol. Ecol.
Avian dispersal
Callens et al. 2011, Mol. Ecol.
Avian dispersal
Callens et al. 2011, Mol. Ecol.
Avian dispersal
Genetic research and dispersal
• difference in polytypy versus monotypy of Chaffinch – Bramling
and European goldfinch - European siskin
Avian migration
Definition of migration
• defined as yearly, large-scale return movement of population
between regular breeding and wintering (or non-breeding) areas
• produces massive redistribution of birds over the earth’ surface
twice each year
• most apparent in seasonal environments, i.e. with contrasting
summer-winter or wet-dry conditions
• in shorebirds, conditions in summer (arctic tundra) and winter
(i.e. tidal areas) may not allow local wintering and breeding,
respectively
Avian migration
Examples of long-distance migrants of birds: (1) Pacific golden plover; (2) Arctic tern;
(3) Swainson’s hawk; (4) Snow goose; (5) North American breeding species; (6) Ruff;
(7) European breeding species; (8) Northern wheatear; (9) Amur falcon; (10) Arctic
warbler; (11) Short-tailed shearwater
Avian migration
Main migration
patterns found in
northern
hemisphere birds,
based on the
degree of
separation
between breeding
and wintering
ranges
Avian migration
Avian migration
Definition of migration
• most marked at high latitudes but also occurs in tropics, i.e.
savannahs and grasslands (mainly related to rainfall patterns)
• insectivorous birds confined to (stable) equatorial rain forest least
migratory (but see nectar- and fruit-eaters and altitudinal
migrants)
• less mobile organisms may cope with seasonal shortages in other
ways (e.g. hibernation)
• year-round resident species exploit year-round available food
supplies, e.g. species in northern coniferous forests feeding on
bark-dwelling arthropods, fruits, seeds, buds, small mammals or
birds (Tits, Treecreepers, Corvids, Finches, Grouse, Raptors, Owls)
Avian migration
Definition of migration
• migratory species feed on active, leaf-dwelling or aerial insects,
or foods that become inaccessible under snow or ice (Warblers,
Hirundines, Ground-feeding finches, Thrushes, Raptors, Waterfowl,
Waders).
• towards equator, wider ranges of food-types remain available
year-round
• various examples of relationship between migration and diet
Avian migration
Migration in relation to diet in west Palaearctic songbirds: % species
breeding at different latitudes that migrate south for the winter
(upper); distances moved by migrants (lower)
Avian migration
Migration in relation to diet in west Palaearctic raptors: % species
breeding at different latitudes that migrate south for the winter
(left); distances moved (right)
Avian migration
Evolution of migration
• can be regarded as product of natural selection and is expected
to evolve whenever it provides a fitness advantage (e.g. due to
fluctuations in food availability)
• autumn migration mainly driven by improved winter survival
• birds may return in spring because temporary abundance of food,
longer days and declining rates of predation on eggs and chicks
with latitude allows raising more young
• spring migration mainly driven by improved breeding success
• compared to survival, reproduction often has more stringent
requirements in terms of specific food needs and predation
avoidance
Avian migration
Evolution of migration
• in some species, full range of variation in migration behaviour
(fully migrant, partial migrant, resident) can be found among
different populations
• main adaptations for long-distance migration (fat reserves,
timing mechanisms and navigation skills/homing behaviour) all
found with somewhat different functions in resident species
• over generations, seasonal timing, directional preferences and
distances for movement can become fixed by natural selection,
leading to fixed migration routes and destinations
Avian migration
Evolution of migration
• role of genetic factors in control of migration has been shown
experimentally (e.g. on Blackcaps by Peter Berthold and
colleagues) by measuring ‘migration restlessness’ (fluttering and
wing-whirring in caged birds during migration seasons) in
‘orientation cages’
Avian migration
Evolution of migration
Avian migration
Evolution of migration
• when cross-breeding birds from different populations, offspring
showed intermediate migration features (timing, duration,
direction, propensity to migrate) within 3-6 generations
• all migration properties can be changed rapidly by natural
selection; e.g. new migration route among Blackcaps
Avian migration
Evolution of migration
Avian migration
Evolution of migration
• other examples of changes in migratory habits confirming that
migration is a dynamic phenomenon subject to change in prevailing
conditions:
migratory to sedentary
• Lesser black-backed gull: large numbers overwinter in Britain,
not prior to 1940
• Eurasian blackbird: British and mid European populations
progressively more sedentary during last century
Avian migration
Evolution of migration
• other examples of changes in migratory habits confirming that
migration is a dynamic phenomenon subject to change in prevailing
conditions:
sedentary to migratory
• European serin: spreading north in early 20th century and
becoming migratory; previously restricted to southern Europe and
resident; recently, migratory population partially resident
• Cattle egret: developing new migrations in newly colonized parts
of Old and New world
• more general: species that extended their breeding ranges into
areas where overwintering is not possible
Avian migration
Evolution of migration
• other examples of changes in migratory habits confirming that
migration is a dynamic phenomenon subject to change in prevailing
conditions:
shortening of migration routes
• North-American Canada geese and European Cranes responded
to increased food due to agricultural changes or creation of refuges
to display short-stopping behaviour
• Barnacle geese established nesting colonies well south of
historical range, shortening their migration by 1300 km
Avian migration
Evolution of migration
• other examples of changes in migratory habits confirming that
migration is a dynamic phenomenon subject to change in prevailing
conditions:
lengthening of migration routes
• Red-breasted geese winter much further from breeding areas
than in 1950s due to land-use changes in former winter sites
Avian migration
Evolution of migration
• other examples of changes in migratory habits confirming that
migration is a dynamic phenomenon subject to change in prevailing
conditions:
timing of migration
• under presumed influence of long-term global warming, many
species arrive earlier and departing later from their breeding areas,
spending more time on their breeding areas
• still, arrival dates fluctuate from year to year in line with local
temperatures
Avian migration
Latitudinal trends and shifts
• key question: what effects do seasonal migrations have on widescale distributions of birds ?
• proportion of migrating species within avifauna’s of different
regions closely correlated with climatic seasonality (e.g.
temperature extremes between hottest and coldest months) and
temporal variation in food availability
• proportion of wholly migratory breeding species increases from
29% (35°N, North Africa) to 83% (80°N, Svalbard), on average
1.3% increase for every degree of latitude
Avian migration
Proportion of
western European
breeding species
at different
latitudes that
migrate south for
the winter
Avian migration
Latitudinal trends and shifts
• similar pattern in eastern North America (1.4% per degree, but
17% more at any given latitude in North America); i.e. similar
slopes but different intercepts
Avian migration
Proportion of
eastern North
American
breeding species
at different
latitudes that
migrate south for
the winter
Avian migration
Latitudinal trends and shifts
• seasonal differential in carrying capacity also varies from W to E
according to changes in climate (warmer and drier summers,
colder winters); e.g. Common starlings on Shetland islands
(residential) and at same latitude in Russia (wholly migratory)
• proportion of Australian migratory species declines with increase
in amount and eveness of annual rainfall (rather than temperature)
Avian migration
Latitudinal trends and shifts
• due to migration, overall species numbers highest during
northern summer (N hemisphere) and austral summer (S
hemisphere); huge latitudinal shift in avifaunal distribution(e.g.
177 migrant landbirds in Afrotropics)
Avian migration
Latitudinal shift
between summer
and winter
distributions of
birds that breed in
Europe. Includes
wintering areas in
Europe, Asia and
Africa
Avian migration
Breeding versus wintering areas
• implies that most species live at greater densities in African
wintering areas than in breeding areas, possibly reflecting
differences in per-unit-area productivity
• individuals may also need less space in Africa when only feeding
themselves; alternatively, warmer weather may decrease individual
daily energy (e.g. Passerine in Africa ca 60% of breeding season
needs); similar pattern in New World warblers
Avian migration
Latitudinal trends and shifts
• landbirds breeding in S hemisphere do not extend N of tropics on
migration, while reverse is true
• Africa: no migration N of Sahara; South-America: nearly no
migration N of Panama; Australasia: no migration beyond
Indonesia
• mainly short-distance (and/or partial, altitudinal, nomadic)
migration by S hemisphere species possibly because encountering
progressively widening land areas/settlement opportunities
towards N (vice versa for N hemisphere species)
Avian migration
Latitudinal trends and shifts
• few migratory bird species have separate breeding populations N
and S of tropics, e.g. Little tern, Whiskered tern (Asia-Australië),
Black stork, Booted eagle (Europe-Africa), Turkey vulture, Black
vulture (N-S America)
• in all species, northern birds winter in S when southern birds are
breeding (in Terns, southern birds winter in N when northern birds
are breeding)
• raises question why same individuals do not breed twice a year
(once in each area)
• possibly because birds moult in winter quarters (mutually
exclusive with breeding in most non-migratory species) and
migratory birds often move within winter quarters in response to
changing food-supplies (avoiding competition with local breeding
residents which are tied to fixed nesting areas)
Avian migration
Latitudinal trends and shifts
• same trends within species, i.e. when comparing proportion of
completely versus partial migrants and distances travelled.
• some species (Fox sparrow, Common ringed plover) show
leapfrog migration (i.e. most northerly breeding individuals
wintering furthest south)
• possibly following last glaciation when breeding populations
spreading north and had to migrate to progressively more southern
latitudes to find sufficient vacant habitat
• persisted until now because of continuing competition
Avian migration
Leapfrog migration in Fox sparrows (left) and Common ringed plovers (right)
Avian migration
Breeding versus wintering areas
• some European migrants show west-east patterns in distribution
(both in breeding/wintering areas); western Lesser whitethroats
and Red-backed shrikes migrate via eastern Europe to eastern
Africa where joined by eastern breeders; opposite pattern in
eastern Pied flycatchers
Avian migration
Loop migration of European Pied flycatchers based on ringing recoveries
Avian migration
Course of first-year migration in White storks from SW (westerly route)
and NW (easterly route) Germany
Avian migration
Parallel migrations within Europe, as shown from recoveries of
Chaffinches ringed in Russia (filled) and Switzerland (open)
Avian migration
Altitudinal migration
• by moving few hundred meters down the sides of a mountain,
birds can achieve as much climatic benefit as by moving several
hundred km to lower latitude, but without extra winter daylength;
e.g. Citril finch, Rosy finch, Three-wattled bellbird, African Olive
pigeon, Olive whistler
• nectar feeders move in reponse to progressively later flowering
at higher elevations
• altitudinal/latitudinal movements not mutually exclusive, while
some birds move upslope in winter (e.g. Blue grouse)
Avian migration
Movements within breeding season
• itinerant breeding species breed in more than one area each
year; e.g. Common redpolls, European siskins, Spanish sparrow,
Common quail (young can mature and breed three months old);
similar examples in North America and Africa (Red-billed quelea)
• may be common in semi-arid regions where birds breed during
particular stage in dry-wet seasonal cycle
• raising of successive broods at different sites on migration route
could occur in a much wider ranges of birds
Avian migration
Movements within non-breeding season
• in some northern species, proportion of birds leaving breeding
ranges (and distances traveled) varies greatly from year to year
(Common redpoll, Bohemian waxwing, Rough-legged buzzard,
Snowy owl); may take form of invasions or irruptions
Avian migration
North American
winter ranges of
Snowy owl and
Common redpoll
Avian migration
Movements within non-breeding season
• hard weather movements especially known from species that
obtain food from water or soft ground (Northern lapwing, Common
starling)
• may return after few days already, possibly to avoid competition
in overcrowded hard weather refuges
• some waterfowl (Common shelduck, Eared grebe) perform ‘moult
migrations’ after breeding (moving to traditional sites that offer
food and safety); may shed all flight feathers at once, remaining
flightless for several weeks
Avian migration
Movements within non-breeding season
• nomadic species exploit sporadic habitats or food resources, i.e.
showing little or no year-to-year consistency in their movement
patterns
• examples include fruit-eating birds of tropical forests (small
scale), rodent-eating owls and raptors of tundra, boreal and arid
regions, boreal seed-eaters, and desert species; e.g. Pallas’
sandgrouse (seeds), Rosy starling (grasshoppers)
• remains unknown how these birds find suitable localities within
such vast areas; dramatic example: Banded stilts (Australia)