Philopatry is the tendency of an organism to stay in or habitually
return to a particular area. The causes of philopatry are numerous,
but natal philopatry, where animals return to their birthplace to
breed, may be the most common. The term derives from the Greek
'home-loving', although in recent years the term has been applied to
more than just the animal's birthplace. Recent usage refers to animals
returning to the same area to breed despite not being born there, and
migratory species that demonstrate site fidelity: reusing stopovers,
staging points, and wintering grounds. Some of the known reasons
for organisms to be philopatric would be for mating (reproduction),
survival, migration, parental care, resources, etc.. In most species
of animals, individuals will benefit from living in groups, because
depending on the species, individuals are more vulnerable to predation
and more likely to have difficulty finding resources and food.
Therefore, living in groups increases a species chances of survival,
which correlates to finding resources and reproducing. Again,
depending on the species, returning to their birthplace where that
particular species occupies that territory is the more favorable
option. The birthplaces for these animals serve as a territory for
them to return for feeding and refuge, like fish from a coral reef.
In an animal behavior study conducted by Paul Greenwood, overall
female mammals are more likely to be philopatric, while male mammals
are more likely to disperse. Male Birds are more likely to
philopatric, while females are more likely to disperse. Philopatry
will favor the evolution of cooperative traits because the direction
of sex has consequences from the particular mating system.
1 Breeding-site philopatry
2 Natal philopatry
2.1 Evolutionary causes of philopatry
2.2 Consequences of philopatry
2.2.2 Cooperative breeding
3 Other variations
4 See also
One type of philopatry is breeding philopatry, or breeding-site
fidelity, and involves an individual, pair, or colony returning to the
same location to breed, year after year. Among animals that are
largely sedentary, breeding-site philopatry is common. It is
advantageous to reuse a breeding site, as there may be territorial
competition outside of the individual’s home range, and since the
area evidently meets the requirements of breeding. Such advantages are
compounded among species that invest heavily in the construction of a
nest or associated courtship area. For example, the megapodes (large,
ground-dwelling birds such as the Australian malleefowl, Leipoa
ocellata) construct a large mound of vegetation and soil or sand to
lay their eggs in. Megapodes often reuse the same mound for many
years, only abandoning it when it is damaged beyond repair, or due to
disturbance. Nest fidelity is highly beneficial as reproducing is time
and energy consuming (malleefowl will tend a mound for five to six
months per year). In colonial seabirds, it has been shown that nest
fidelity depends on multi-scale information, including the breeding
success of the focal breeding pair, the average breeding success of
the rest of the colony, and the interaction of these two scales.
Breeding fidelity is also well documented among species that migrate
or disperse after reaching maturity. Birds, in particular, that
disperse as fledglings will take advantage of exceptional navigational
skills to return to a previous site. Philopatric individuals
exhibit learning behaviour, and do not return to a location in
following years if a breeding attempt is unsuccessful. The
evolutionary benefits of such learning are evident: individuals that
risk searching for a better site will not have lower fitness than
those that persist with a poor site.
Philopatry is not homogenous
within a species, with individuals far more likely to exhibit
philopatry if the breeding habitat is isolated. Similarly,
non-migratory populations are more likely to be philopatric that those
In species that exhibit lifelong monogamous pair bonds, even outside
of the breeding season, there is no bias in the sex that is
philopatric. However, among polygynous species that disperse
(including those that find only a single mate per breeding season),
there is a much higher rate of breeding-site philopatry in males than
females among birds, and the opposite bias among mammals. Many
possible explanations for this sex bias have been posited, with the
earliest accepted hypothesis attributing the bias to intrasexual
competition, and territory choice. The most widely accepted
hypothesis is that proposed by Greenwood (1980). Among birds, males
invest highly in protecting resources – a territory – against
other males. Over consecutive seasons, a male that returns to the same
territory has higher fitness than one that is not philopatric.
Females are free to disperse, and assess males. Conversely, in
mammals, the predominant mating system is one of matrilineal social
Males generally invest little in the raising of offspring, and compete
with each other for mates rather than resources. Thus dispersing can
result in reproductive enhancement, as greater access to females is
available. On the other hand, the cost of dispersal to females is
high, and thus they are philopatric. This hypothesis also applies to
natal philopatry, but is primarily concerned with breeding-site
fidelity. A more recent hypothesis builds on Greenwood’s findings,
suggesting that parental influence may play a large role. Because
birds lay eggs, adult females are at risk of being cuckolded by their
daughters, and thus would drive them out. On the other hand, young
male mammals pose a threat to their dominant father, and so are driven
to disperse while young.
This page discusses the evolutionary reasons for philopatry. For the
mechanisms of philopatry, see Natal homing
Natal philopatry commonly refers to the return to the area the animal
was born in, or to animals remaining in their natal territory. It is a
form of breeding-site philopatry. The debate over the evolutionary
causes remains unsettled. The outcomes of natal philopatry may be
speciation, and, in cases of non-dispersing animals, cooperative
breeding. Natal philopatry is the most common form of philopatry in
females because it decreases competition for mating and increases the
rate of reproduction and a higher survival rate for offspring.
Natal philopatry also leads to a kin-structured population, which is
when the population is more genetically related than less related
between individuals in a species. This can also lead to inbreeding and
a higher rate of natural and sexual selection within a population.
Evolutionary causes of philopatry
The exact causes for the evolution of natal philopatry are unknown.
Two major hypotheses have been proposed. Shields (1982) suggested that
philopatry was a way of ensuring inbreeding, in a hypothesis known as
the optimal-inbreeding hypothesis. He argued that, since
philopatry leads to the concentration of related individuals in their
birth areas, and thus reduced genetic diversity, there must be some
advantage to inbreeding – otherwise the process would have been
evolutionary detrimental and would not be so prevalent. The major
beneficial outcome under this hypothesis is the protection of a local
gene complex that is finely adapted to the local environment.
Another proposed benefit is the reduction the cost of meiosis and
recombination events. Under this hypothesis, non-philopatric
individuals would be maladapted and over multi-generational time,
philopatry within a species could become fixed. Evidence for the
optimal-inbreeding hypothesis is found in outbreeding depression.
Outbreeding depression involves reduced fitness as a result of random
mating, which occurs due to the breakdown of coadapted gene complexes
by combining allele that do not cross well with those from a different
subpopulation. However, it is important to note that outbreeding
depression becomes more detrimental the longer (temporally) that
subpopulations have been separated, and that this does hypothesis does
not provide an initial mechanism for the evolution of natal
A second hypothesis explains the evolution of natal philopatry as a
method of reducing the high costs of dispersal among offspring. A
review of records of natal philopatry among passerine birds found that
migrant species showed significantly less site fidelity than sedentary
birds. Among migratory species, the cost of dispersal is paid
either way. If the optimal-inbreeding hypothesis was correct, the
benefits of inbreeding should result in philopatry among all species.
Inbreeding depression is a phenomenon whereby deleterious alleles
become fixed more easily within an inbreeding population.
Inbreeding depression is demonstrably costly and accepted by most
scientists as a greater cost than those of outbreeding depression.
Within a species, there has also been found to be variation in rates
of philopatry, with migratory populations exhibiting low levels of
philopatry – further suggesting that the ecological cost of
dispersal, rather than genetic benefits of either inbreeding or
outbreeding, is the driver of natal philopatry.
A number of other hypotheses exist. One such is that philopatry is a
method, in migratory species, of ensuring that the sexes interact in
breeding areas, and that breeding actually occurs. A second is
that philopatry provides a much higher chance of breeding success.
Strict habitat requirements – whether due to a precisely adapted
genome or not – mean that individuals that return to a site are more
familiar with it, and may have more success in either defending it, or
locating mates. This hypothesis does not justify whether philopatry
is due to an innate behaviour in each individual, or to learning;
however it has been shown that, in most species, older individuals
show higher site fidelity. Neither of these hypotheses is as
widely accepted as the optimal-inbreeding or dispersal hypotheses, but
their existence indicates that the evolutionary causes of natal
philopatry have still not been conclusively demonstrated.[citation
Consequences of philopatry
A major outcome of multi-generational natal philopatry is genetic
divergence and, ultimately, speciation. Without genetic exchange,
geographically and reproductively isolated populations may undergo
genetic drift. Such speciation is most evident on islands. For mobile
island-breeding animals, finding a new breeding location may be beyond
their means. In combination with a small population, as may occur due
to recent colonisation, or simply restricted space, genetic drift can
occur on shorter timescales than is observable in mainland species.
The high levels of endemism on islands have been attributed to these
Substantial evidence for speciation due to natal philopatry has been
gathered in studies of island-nesting albatross. Genetic difference is
most often detected in microsatellites in mitochondrial DNA. Animals
that spend much of their time at sea, but which return to land to
breed exhibit high levels of natal philopatry and subsequent genetic
drift between populations. Many species of albatross do not breed
until 6–16 years of age. Between leaving their birth island, and
their return, they fly hundreds of thousands of kilometres. High
levels of natal philopatry have been demonstrated via mark-recapture
data. For example, more than 99% of
Laysan albatross (Phoebastria
immutabilis) in a study returned to exactly the same nest in
consecutive years. Such site-specificity can lead to speciation,
and has also been observed in the earliest stages of this process. The
shy albatross (Thalassarche [cauta] cauta) was shown to have genetic
differences in its microsatellites between three breeding colonies
located off the coast of Tasmania. The differences are not
currently sufficient to propose identifying the populations as
distinct species; however divergence is likely to continue without
Not all isolated populations will show evidence of genetic drift.
Genetic homogeneity can be attributed to one of two explanations, both
of which indicate that natal philopatry is not absolute within a
species. Firstly, a lack of divergence may be due to founder effects,
which explains how individuals that start new populations carry the
genes of their source population. If only a short (in evolutionary
timescales) period of time has passed, insufficient divergence may
have occurred. For example, study of mitochondrial DNA microsatellites
found no significant difference between colonies of black-browed
albatross (T. melanophrys) on the Falkland Islands and Campbell
Island, despite the sites being thousands of kilometres apart.
Observational evidence of white-capped albatross (T. [cauta] steadi)
making attempts to build nests on a south Atlantic Island, where the
species had never been previously recorded, demonstrate that range
extension by roaming sub-adult birds is possible. Secondly, there
may be sufficient gene exchange as to prevent divergence. For example,
isolated (yet geographically close) populations of the Buller’s
albatross (T. bulleri bulleri) have been shown to be genetically
similar. This evidence has only recently, for the first time, been
supported by mark-recapture data, which showed one bird marked on one
of the two breeding islands was nesting on the other island.[citation
Due to the dispersal capabilities of albatross, distance between
populations does not appear to be a determining factor in
divergence. Actual speciation is likely to occur very slowly, as
the selective pressures on the animals are the same for the vast
majority of their lives, which is spent at sea. Small mutational
changes in non-nuclear DNA that become fixed in small populations are
likely to be the major driver of speciation. That there is minimal
structural morphological difference between the genetically distinct
populations is evidence for random genetic drift, rather than
directional evolution due to natural selective pressure.[citation
Speciation through natal philopatry is a self-reinforcing process.
Once genetic differences are sufficient, different species may be
unable to interbreed to produce viable offspring. As a result,
breeding could not occur anywhere except natal island, strengthening
philopatry and ultimately leading to even greater genetic
Main article: Cooperative breeding
Philopatric species that do not migrate may evolve to breed
cooperatively. Kin selection, of which cooperative breeding is a form,
explains how individual offspring provide care for further offspring
produced by their relatives. Animals that are philopatric to
birthsites have increased association with family members, and, in
situations where inclusive fitness is increased through cooperative
breeding, may evolve such behaviour, as it will incur evolutionary
benefits to families that do. Inclusive fitness is the sum of all
direct and indirect fitness, where direct fitness is defined as the
amount of fitness gained through producing offspring. Indirect fitness
is defined as the amount of fitness gained through aiding related
Cooperative breeding is a hierarchical social system characterized by
a dominant breeding pair surrounded by subordinate helpers. The
dominant breeding pair and their helpers experience costs and benefits
from using this system.
Costs for helpers include a fitness reduction, increased territory
defense, offspring guarding and an increased cost of growth. Benefits
for helpers include a reduced chance of predation, increased foraging
time, territory inheritance, increased environmental conditions and an
inclusive fitness.
For the breeding pair, costs include increased mate guarding and
suppression of subordinate mating. Breeders receive benefits as
reductions in offspring care and territory maintenance. Their primary
benefit is an increased reproductive rate and survival.[citation
Cooperative breeding causes the reproductive success of all sexually
mature adults to be skewed towards one mating pair. This means the
reproductive fitness of the group is held within a select few breeding
members and helpers have little to no reproductive fitness. With
this system, breeders gain an increased reproductive, while helpers
gain an increased inclusive fitness.
Cooperative breeding, like speciation, can become a self-reinforcing
process for a species. If the fitness benefits result in higher
inclusive fitness of a family than the fitness of a non-cooperative
family, the trait will eventually become fixed in the population. Over
time, this may lead to the evolution of obligate cooperative breeding,
as exhibited by the Australian mudnesters and Australo-Papuan
babblers. Obligate cooperative breeding requires natally philopatric
offspring to assist in raising offspring – breeding is unsuccessful
without such help.
Migrating animals also exhibit philopatry to certain important areas
on their route; staging areas, stop-overs, molting areas and wintering
Philopatry is generally believed to help maintain the
adaptation of a population to a very specific environment (i.e., if a
set of genes has evolved in a specific area, individuals that fail to
return to that area may do poorly elsewhere, so natural selection will
favor those who exhibit fidelity).
The level of philopatry varies within migratory families and
The term is sometimes also applied to animals that live in nests but
do not remain in them during an unfavorable season (e.g., the winter
in the temperate zone, or the dry season in the tropics), and leave to
find hiding places nearby to pass the inactive period (common in
various bees and wasps); this is not migration in the usual sense, as
the location of the hiding place is effectively random and unique
(never located or revisited except by accident), though the navigation
skills required to relocate the old nest site may be similar to those
of migrating animals.
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