Cooperative breeding

Cooperative breeding is a social system characterized by alloparental care: offspring receive care not only from their parents, but also from additional group members, often called helpers.[1] Cooperative breeding encompasses a wide variety of group structures, from a breeding pair with helpers that are offspring from a previous season,[2] to groups with multiple breeding males and females (polygynandry) and helpers that are the adult offspring of some but not all of the breeders in the group,[3] to groups in which helpers sometimes achieve co-breeding status by producing their own offspring as part of the group's brood.[4] Cooperative breeding occurs across taxonomic groups including birds,[5] mammals,[6] fish,[7] and insects.[8]

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. 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 individuals offspring, that is relatives are able to indirectly pass on their genes through increasing the fitness of related offspring.[9] This is also called kin selection.[10]

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.

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.[11] With this system, breeders gain an increased reproductive fitness, while helpers gain an increased inclusive fitness.[11]

Evolution

Many hypotheses have been presented to explain the evolution of cooperative breeding. The concept behind cooperative breeding is the forfeiting of an individual's reproductive fitness to aid the reproductive success of others. This concept is hard to understand and the evolution of cooperative breeding is important, but difficult to explain. Most hypotheses aim to determine the reason helpers selectively reduce their fitness and take on an alloparental role.

Kin selection is the evolutionary strategy of aiding the reproductive success of related organisms, even at a cost to the own individual's direct fitness. Hamilton's rule (rB−C>0) explains that kin selection will exist if the genetic relatedness (r) of the aided recipient to the aiding individual, times the benefit to the aid recipient (B) is greater than the cost to the aiding individual(C).[9] For example, the chestnut-crowned babbler (Pomatostomus ruficeps) has been found to have high rates of kin selection. Helpers are predominantly found aiding closely related broods over nonrelated broods.[12] Additional species such as Neolamprologus pulcher have shown that kin selection is a dominant driving force for cooperative breeding.[12]

Group augmentation presents a second hypothesis towards the evolution of cooperative breeding. This hypothesis suggests that increasing the size of the group through the addition of helpers aids in individual survival and may increase the helper's future breeding success.[13] Group augmentation is favored if the grouping provides passive benefits for helpers in addition to inclusive fitness.[14] By group augmenting, each individual member reduces their chances of becoming a victim of predation. Additionally, an increase in members reduces each helper's duration as a sentinel (standing upon a high surface to survey for predators) or babysitting (guarding the offspring and den). The reduction in these guarding behaviors enables helpers to forage for longer periods.[15]

Lukas et al. proposed an evolutionary model for cooperative breeding, which linked the coevolution of polytocy, production of multiple offspring, and monotocy, production of single offspring, with the evolution of cooperative breeding. The model is based on the evolution of larger litters forcing the need for helpers to maintain the high reproductive costs, thus leading to cooperative breeding. Lukas et al. suggests polytocy may have encouraged the evolution of cooperative breeding. Their proposed model suggests the transition from monotocy to polytocy is favorable. Additionally, they found the transition from polytocy without cooperative breeding to polytocy with cooperative breeding is highly favorable. This suggests cooperative breeding evolved from noncooperative breeding monotocy to cooperative breeding polytocy.[1]

Today, there is growing support for the theory that cooperative breeding evolved by means of some form of mutualism or reciprocity. Mutualism is a form of symbiosis that is beneficial to both involved organisms. Mutualism has many forms and can occur when the benefits are immediate or deferred, when individuals exchange beneficial behaviors in turn, or when a group of individuals contribute to a common good, where it may be advantageous for all group members to help raise young. When a group raises young together, it may be advantageous because it maintains or increases the size of the group.[16] The greatest amount of research has been invested in reciprocal exchanges of beneficial behavior through the iterated prisoner's dilemma. In this model, two partners can either cooperate and exchange beneficial behavior or they can defect and refuse to help the other individual.[16]

Environmental conditions

Environmental conditions govern whether offspring disperse from their natal group or remain as helpers. Food or territory availability can encourage individuals to disperse and establish new breeding territories, but unfavorable conditions promote offspring to remain at the natal territory and become helpers to obtain an inclusive fitness.[17] Additionally, remaining at the natal territory enables offspring to possibly inherit the breeding role and/or territory of their parents.[18]

A final factor influencing cooperative breeding is sexual dispersal. Sexual dispersal is the movement of one sex, male or female, from the natal territory to establish new breeding grounds. This is highly regulated by the reproductive costs in producing a male versus a female offspring. Maternal investment within female offspring may be considerably higher than male offspring for one species, or vice versa for another. During unfavorable conditions the cheaper sex will be produced at higher ratios.[19]

A second factor affecting the sexual dispersal is the difference in ability of each sex to establish a new breeding territory. Carrion crow (Corvus corone) were found to produce more female offspring in favorable environmental conditions. Female Corvus corone have been found to establish successful breeding territories at a higher rate than males. Male Corvus corone were produced at a higher rate under unfavorable conditions. Males were found to remain at the natal territory and become helpers.[20] Thus, if environmental conditions favor the dispersal of a specific sex it is considered the dispersal sex. If environmental conditions are unfavorable females may produce the philopatric sex, therefore generating more helpers and increasing the occurrence of cooperative breeding.[20]

Costs

Breeders

Breeder costs consist of prenatal care, postnatal care and maintenance of breeding status. Prenatal care is the amount of maternal investment during fetus gestation and postnatal care is the investment following birth. Examples of prenatal care are fetal, placentae, uterus and mammary tissue development. Postnatal examples are lactation, food provisions and guarding behavior.[19]

Dominant males and females exhibit suppressive behaviors towards subordinates to maintain their breeding status. These suppressive acts are dependent upon the sex ratio of helpers. Therefore, the costs will be altered depending upon the helpers. For example, if there are more male helpers as compared to females, then the dominant male will suppress subordinate males and experience a higher cost. The opposite is true for females. Breeders will even suppress subordinates from mating with other subordinates.[21]

Helpers

The cost to helpers varies depending upon presence or absence of related offspring. The presence of offspring has been found to increase the helper’s cost by the helper contributing to guard behaviors.[22] Guarding behaviors, such as babysitting, can cause individuals to experience weight loss on an exponential scale depending upon the duration of the activity. Other activities, such as sentinel behavior and bipedal surveillance, cause helpers to have reduced foraging intervals inhibiting their weight gains. The reduced foraging behavior and increased weight loss reduces their chance to breed successfully, but increase their inclusive fitness by increasing the survival of related offspring.[11][23][24]

Helpers contribute depending upon the cost. The act of helping requires an allocation of energy towards actually performing the behavior. Prolonged allocation of energy may greatly impact a helper’s growth.[24] In banded mongoose (Mungos mungo) juvenile male helpers contribute far less than females. This is due to a difference in the age of sexual maturity.[24] Female banded mongooses reach sexual maturity at one year of age, but males reach sexual maturity at two years of age. The difference in age causes the prolonged energy allocation to be detrimental to a specific sex.[24]

Male juvenile Mungos mungo may reduce helping behaviors until sexual maturity is reached. Similarly, if there is a lack of food due to environmental conditions, such as reduced rainfall, the degree of helper input may be reduced greatly within juveniles. Adults may maintain their full activity because they are sexually mature.[18]

Additionally, the costs of being a helper can be more detrimental to one sex. For example, territorial defense costs are generally male dependent and lactation is female dependent. Meerkats (Suricata suricatta) have exhibited male territory defense strategies, where male helpers will fend off intruding males to prevent such intruders from mating with subordinates or dominant females.[25] Additionally, subordinate female pregnant helpers are sometimes exiled from the group by a dominant female. This eviction causes the subordinate female to have an abortion, which frees up resources such as lactation and energy that can be used to help the dominant female and her pups.[10]

Rarely, a female helper or breeder will defend the territory while males are present. This suggests specific helping costs, such as territory defense, is rooted to one sex.[13]

Benefits

Breeders

Cooperative breeding reduces the costs of many maternal investments for breeding members. Helpers aid the breeding females with provisioning, lactation stress, guarding of offspring and prenatal investment.[13][19][26] Increasing the number of helpers enables a breeding female or male to maintain a healthier physique, higher fitness, increased lifespan and brood size.[22][27]

Female helpers can aid in lactation, but all helpers, male or female, can aid in food provisioning.[18][19] Helper food provisioning reduces the need for the dominant breeding pair to return to the den, thus allowing them to forage for longer periods. The dominant female and male will adjust their care input, or food provisioning, depending on the degree of activity of the helpers.[18]

The presence of helpers allows the breeding female to reduce her prenatal investment in the offspring, which may lead to altricial births; altricial is the production of young which are dependent upon adult aid to survive. This enables the breeding female to retain energy to be used within a new breeding attempt.[19] Overall, the addition of helpers to a breeding pair encourages multiple reproductions per year, and increases the rate of successful reproduction.[27]

Male breeders can benefit directly from reproducing with subordinate females and aiding in raising the young. This allows the male to obtain a “repayment investment” within these subordinate offspring. These offspring have a higher chance to become helpers once sexual maturity is reached. Thus, paying into their care will increase the dominant male’s overall fitness in the future. This act ensures the dominant male subordinate helpers for future reproduction.[28]

Helpers

Helpers primarily benefit from an inclusive fitness.[1][17][23] Helpers maintain an inclusive fitness while aiding related breeders and offspring.[11] This type of kinship may lead to inheritance of quality foraging and breeding territories, which will increase the future fitness of helpers.[29] Additional, helpers experience an increased chance of being helped if they were once a helper.[27]

Finally, helpers benefit from group interactions, such as huddling for thermodynamic benefits. These interactions provide necessary elements to survive.[15][29] They may also benefit from the increased group interaction on the level of cognitive concern for one another increasing their overall life span and survival.[30]

Biological examples

Birds

Approximately eight percent of bird species are known to regularly engage in cooperative breeding, mainly among the Coraciiformes, Piciformes, basal Passeri and Sylvioidea.[31] Only a small fraction of these, for instance the Australian mudnesters, Australo-Papuan babblers and ground hornbills, are however absolutely obligately cooperative and cannot fledge young without helpers.[32]

The benefits of cooperative breeding in birds have been well-documented. One example is the azure-winged magpie (Cyanopica cyanus), in which studies found that the offspring’s cell-mediated immune response was positively correlated with increase in the number of helpers at the nest.[33] Studies on cooperative breeding in birds have also shown that high levels of cooperative breeding are strongly associated with low annual adult mortality and small clutch sizes, though it remains unclear whether cooperative breeding is a cause or consequence.[34] It was originally suggested that cooperative breeding developed among bird species with low mortality rates as a consequence of “overcrowding” and thus fewer opportunities to claim territory and breed. However, many observers today believe cooperative breeding arose because of the need for helpers to rear young in the extremely infertile and unpredictable environments[35] of Australia and sub-Saharan Africa under the rare favourable conditions.[31]

Meerkats

Suricata.suricatta.with.young.2
An older female watches over pups while alpha female is away.

Meerkats become reproductively active at one year of age and can have up to four litters per year. However, usually it is the alpha pair that reserves the right to mate and will usually kill any young that is not their own. While the alpha female is away from the group, females that have never reproduced lactate and hunt in order to feed the pups, as well as watch, protect, and defend them from predators. Although it was previously thought that a meerkat’s contribution to a pup’s diet depended on the degree of relatedness, it has been found that helpers vary in the number of food items they give to pups. This variation in food offering is due to variation in foraging success, sex, and age.[36] Research has additionally found that the level of help is not correlated to the kinship of the litters they are rearing.[37]

Canids

Cooperative breeding has been described in several canid species[38] including red wolves,[39] Arctic foxes[40] and Ethiopian wolves.[41]

Primates

Cooperative breeding entails one or more individuals, usually females, acting as "helpers" to one or a few dominant female breeders, usually helpers' kin. This sociosexual system is rare in primates, so far demonstrated among Neotropical callitricids, including marmosets and tamarins. Cooperative breeding requires "repression" of helpers' reproduction, by pheromones emitted by a breeder, by coercion, or by self-restraint. Sarah Blaffer Hrdy believes that cooperative breeding is an ancestral trait in humans, a controversial proposition.

References

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  14. ^ Kokko, H.; Johnstone, R. A. (2001). "The evolution of cooperative breeding through group augmentation". Proceedings of the Royal Society B: Biological Sciences. 268 (1463): 187–196. doi:10.1098/rspb.2000.1349. PMC 1088590. PMID 11209890.
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  21. ^ Mitchell, J. S.; Jutzeler, E.; Heg, D.; Taborsky, M. (2009). "Gender Differences in the Costs that Subordinate Group Members Impose on Dominant Males in a Cooperative Breeder". Ethology. 115 (12): 1162–1174. doi:10.1111/j.1439-0310.2009.01705.x.
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  25. ^ Pauw, A (2000). "Parental care in a polygynous group of bat-eared foxes, Otocyon megalotis ( Carnivora : Canidae )". African Zoology. 35: 139–145. doi:10.1080/15627020.2000.11407200.
  26. ^ Nichols, H. J.; Amos, W.; Cant; Bell, M. B. V.; Hodge, S. J. (2010). "Top males gain high reproductive success by guarding more successful females in a cooperatively breeding mongoose". Animal Behaviour. 80 (4): 649–657. doi:10.1016/j.anbehav.2010.06.025.
  27. ^ a b c Charmantier, A.; Keyser, A. J.; Promislow, D. E. L. (2007). "First evidence for heritable variation in cooperative breeding behaviour". Proceedings: Biological Sciences. 274 (1619): 1757–61. doi:10.1098/rspb.2007.0012. PMC 2493572. PMID 17490945.
  28. ^ Liedtke, J.; Fromhage, L. (2012). "When should cuckolded males care for extra-pair offspring?". Proceedings: Biological Sciences. 279 (1739): 2877–82. doi:10.1098/rspb.2011.2691. PMC 3367774. PMID 22438493.
  29. ^ a b Sorato, E.; Gullett, P. R.; Griffith, S. C.; Russell, A. F. (2012). "Effects of predation risk on foraging behaviour and group size: adaptations in a social cooperative species". Animal Behaviour. 84 (4): 823–834. doi:10.1016/j.anbehav.2012.07.003.
  30. ^ Isler, K.; Van Schaik, C. P. (2012). "How Our Ancestors Broke through the Gray Ceiling" (PDF). Current Anthropology. 53: S453–S465. doi:10.1086/667623.
  31. ^ a b Jetz, Walter; Rubinstein, Dustin R. (2011). "Environmental Uncertainty and the Global Biogeography of Cooperative Breeding in Birds" (PDF). Current Biology. 21 (1): 72–8. doi:10.1016/j.cub.2010.11.075. PMID 21185192.
  32. ^ See Cockburn, Andrew; "Prevalence of different modes of parental care in birds"
  33. ^ Valencia, Juliana; Elena Solis; Gabrielle Sorci; Carlos de la Cruz (2006). "Positive correlation between helpers at nest and nestling immune response in cooperative breeding bird". Behavioral Ecology and Sociobiology. 60 (3): 399–404. doi:10.1007/s00265-006-0179-z.
  34. ^ Arnold, Kathryn E.; Ian P. F. Owens (7 May 1998). "Cooperative breeding in birds: a comparative test of the life history hypothesis". Proceedings: Biological Sciences. 265 (1398): 739–745. doi:10.1098/rspb.1998.0355. PMC 1689041.
  35. ^ See McMahon T.A. and Finlayson, B.; Global Runoff: Continental Comparisons of Annual Flows and Peak Discharges. ISBN 3-923381-27-1
  36. ^ Clutton-Brock, T.H. "Individual Contributions to babysitting in a cooperative mongoose, Suricata suricatta" (PDF).
  37. ^ Clutton-Brock, T.H.; Brotherton, P.N.M.; O'Riain, M.J.; Griffin, A.S.; Gaynor, D.; Kansky, R.; Sharpe, L.; McIlrath, G.M. (2000). "Contributions to cooperative rearing in meerkats". Animal Behaviour. 61 (4): 705–710. doi:10.1006/anbe.2000.1631.
  38. ^ Moehlman, Patricia D., and H. E. R. I. B. E. R. T. Hofer. "Cooperative breeding, reproductive suppression, and body mass in canids." Cooperative breeding in mammals (1997): 76-128.
  39. ^ Sparkman, Amanda M.; et al. (2010). "Direct fitness benefits of delayed dispersal in the cooperatively breeding red wolf (Canis rufus)". Behavioral Ecology. 22 (1): 199–205. doi:10.1093/beheco/arq194.
  40. ^ Kullberg, Cecilia; Angerbjörn, Anders (1992). "Social Behaviour and Cooperative Breeding in Arctic Foxes, Alopex lagopus (L.), in a Semi‐natural Environment" (PDF). Ethology. 90 (4): 321–335. doi:10.1111/j.1439-0310.1992.tb00843.x.
  41. ^ van Kesteren, Freya; et al. (2013). "The physiology of cooperative breeding in a rare social canid; sex, suppression and pseudopregnancy in female Ethiopian wolves" (PDF). Physiology & Behavior. 122: 39–45. doi:10.1016/j.physbeh.2013.08.016. PMID 23994497.
Acanthiza

Acanthiza is a genus of passeriform birds, most endemic to Australia, but with two species (A. murina and A. cinerea) restricted to New Guinea. These birds are commonly known as thornbills. They are not closely related to species in the hummingbird genera Chalcostigma and Ramphomicron, which are also called thornbills.

They are found primarily in Australia and have a thin long beak. Colloquially the thornbill is sometimes referred to as a “tit” by locals, but in reality the Australian continent lacks any true tits, albeit Acanthiza species do show some similarities with tits in their behavior. They have a similar role as small insect-eating birds with titmice and kinglets. Like tits, Thornbills live in small groups foraging amidst trees and shrubs, and feed in a similar manner. Cooperative breeding is recorded from most species except the brown and Tasmanian thornbills.The habitat preferences of the group vary from dense forest to open saltbush and bluebush plains.

Acanthiza follow a very characteristic undulating path when flying. Their diet is formed essentially of little insects and plant lice that these birds glean from foliage. They are also exceptional acrobats that are easily able to stay head downward like tits do.

The nest of the Acanthiza is a large dome-shaped construction, completely enclosed except for a side hole, just like that of the long-tailed tit; however Acanthiza adds to it an additional room whose function is unknown. It is somewhat similar to the Aegithalidae in combining long incubation periods with highly synchronous hatching. This combination, normally impossible due to intense competition for food, occurs because parents and (usually) helpers can organise food supply in such a manner that sibling competition for food is virtually absent.The number of eggs usually ranges from two to four, and the incubation period is around twenty days with laying intervals of two days. The length of an adult bird is 8 to 10 centimetres (3.1 to 3.9 in).

Acorn woodpecker

The acorn woodpecker (Melanerpes formicivorus) is a medium-sized woodpecker, 21 cm (8.3 in) long, with an average weight of 85 g (3.0 oz).

Aegithalidae

The bushtits or long-tailed tits, Aegithalidae, are a family of small, drab passerine birds with moderately long tails. The family contains 13 species in four genera, all but one of which are found in Eurasia. Bushtits are active birds, moving almost constantly while they forage for insects in shrubs and trees. During non-breeding season, birds live in flocks of up to 50 individuals. Several bushtit species display cooperative breeding behavior, also called helpers at the nest.

Alloparenting

Alloparenting (also referred to as alloparental care) is a term used to classify any form of parental care provided by an individual towards a non-descendant young. Non-descendant refers to any young who is not the direct genetic offspring of the individual, but does not exclude related young such as siblings or grandchildren. Individuals providing this care are referred to using the neutral term of alloparent (or 'helper').Alloparental care encapsulates a diverse range of parenting systems across a range of animal groups and social structures. The alloparent-young relationship can be mutualistic or parasitic, and between or within species. Cooperative breeding, joint brood care, reciprocal allonursing, brood parasitism and cuckoldry represent situations in which alloparenting plays a role.

Butcherbird

Butcherbirds are Australian magpie-like birds. Most are found in the genus Cracticus, but the black butcherbird is placed in the monotypic genus Melloria. They are native to Australasia. Together with three species of currawong and two species of peltops, butcherbirds and the Australian magpie form the subfamily Cracticinae in the family Artamidae.

Butcherbirds are large songbirds, being between 30 and 40 cm (12–16 in) in length. Their colour ranges from black-and-white to mostly black with added grey plumage, depending on the species. They have a large, straight bill with a distinctive hook at the end which is used to skewer prey. They have high-pitched complex songs, which are used to defend their essentially year-round group territories: unlike birds of extratropical Eurasia and the Americas, both sexes sing prolifically.Butcherbirds are insect eaters for the most part, but will also feed on small lizards and other vertebrates. They get their name from their habit of impaling captured prey on a thorn, tree fork, or crevice. This "larder" is used to support the victim while it is being eaten, to store prey for later consumption, or to attract mates.

Butcherbirds are the ecological counterparts of the shrikes, mainly found in Eurasia and Africa, which are only distantly related, but share the "larder" habit; shrikes are also sometimes called "butcherbirds". Butcherbirds live in a variety of habitats from tropical rainforest to arid shrubland. Like many similar species, they have adapted well to urbanisation and can be found in leafy suburbs throughout Australia. They are opportunistic, showing little fear and readily taking food offerings to the point of becoming semi-tame.

Female butcherbirds lay between two and five eggs in a clutch, with the larger clutch sizes in more open-country species. Except in the rainforest-dwelling hooded and black butcherbirds, cooperative breeding occurs, with many individuals delaying dispersal to rear young. The nest is made from twigs, high up in a fork of a tree. The young will remain with their mother until almost fully grown. They tend to trail behind their mother and "squeak" incessantly while she catches food for them.

Corvida

The "Corvida" were one of two "parvorders" contained within the suborder Passeri, as proposed in the Sibley-Ahlquist taxonomy, the other being Passerida. Standard taxonomic practice would place them at the rank of infraorder.

More recent research suggests that this is not a distinct clade—a group of closest relatives and nothing else—but an evolutionary grade instead. As such, it is abandoned in modern treatments, being replaced by a number of superfamilies that are considered rather basal among the Passeri.

It was presumed that cooperative breeding—present in many or most members of the Maluridae, Meliphagidae, Artamidae and Corvidae, among others—is a common apomorphy of this group. But as evidenced by the updated phylogeny, this trait is rather the result of parallel evolution, perhaps because the early Passeri had to compete against many ecologically similar birds (see near passerine).

Dallas World Aquarium

The Dallas World Aquarium is a for-profit aquarium and zoo located in the West End Historic District of downtown Dallas, Texas, USA. It aids conservation and education by housing many animals that are threatened or endangered as part of a cooperative breeding program with other zoos around the world. It has been an accredited member of the Association of Zoos and Aquariums since 1997, and is a member of the World Association of Zoos and Aquariums.

Group augmentation

In animal behaviour, the hypothesis of group augmentation is where animals living in a group behave so as to increase the group's size, namely through the recruitment of new members. Such behaviour could be selected for if larger group size increases the chance of survival of the individuals in the group. Supported hypothesis of selection mechanisms towards increasing group size currently exist, in helping raise other animals' offspring (alloparental care) and performing other cooperative breeding acts including kin selection. It is currently proposed that group augmentation may be another mechanism (closely related/connected to cooperative breeding) which occurs through the recruiting of new group members and helping of unrelated individuals within a group.

Mexican jay

The Mexican jay (Aphelocoma wollweberi) formerly known as the gray-breasted jay, is a New World jay native to the Sierra Madre Oriental, Sierra Madre Occidental, and Central Plateau of Mexico and parts of the southwestern United States. In May 2011, the American Ornithologists' Union voted to split the Mexican jay into two species, one retaining the common name Mexican jay and one called the Transvolcanic jay. The Mexican jay is a medium-sized jay with blue upper parts and pale gray underparts. It resembles the western scrub jay, but has an unstreaked throat and breast. It feeds largely on acorns and pine nuts, but includes many other plant and animal foods in its diet. It has a cooperative breeding system where the parents are assisted by other birds to raise their young. This is a common species with a wide range and the International Union for Conservation of Nature has rated its conservation status as being of "least concern".

Mohoua

Mohoua is a small genus of three bird species endemic to New Zealand. The scientific name is taken from mohua – the Māori name for the Yellowhead. Their taxonomic placement has presented problems: They have typically been placed in the Pachycephalidae family (whistlers), but in 2013 it was established that they are best placed in their own family, Mohouidae.All three species display some degree of sexual dimorphism in terms of size, with the males being the larger of the two sexes. Mohoua are gregarious (more so outside the breeding season) and usually forage in groups . They also forage in mixed species flocks at times, frequently forming the nucleus of such flocks. Social organization and behaviour is well documented for all three Mohoua species; cooperative breeding has been observed in all three species and is common in the Whitehead and Yellowhead. The three species of this genus are the sole hosts for the Long-tailed Cuckoo which acts as a brood parasite upon them, pushing their eggs out of the nest and laying a single one of its own in their place so that they take no part in incubation of their eggs or in raising their young.

Philopatry

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.

Pygmy falcon

The pygmy falcon, or African pygmy falcon (Polihierax semitorquatus), is a falcon that lives in eastern and southern Africa and is the smallest raptor on the continent. As a small falcon, only 19 to 20 cm long, it preys on insects, small reptiles, and small mammals.

Reproductive success

Reproductive success is defined as an individual's production of offspring per breeding event or lifetime. This is not limited by the number of offspring produced by one individual, but also the reproductive success of these offspring themselves. Reproductive success is different from fitness in that individual success is not necessarily a determinant for adaptive strength of a genotype since the effects of chance and the environment have no influence on those specific genes. Reproductive success turns into a part of fitness when the offspring are actually recruited into the breeding population. If offspring quantity is not correlated with quality this holds up, but if not then reproductive success must be adjusted by traits that predict juvenile survival in order to be measured effectively. Quality and quantity is about finding the right balance between reproduction and maintenance and the disposable soma theory of aging tells us that a longer lifespan will come at the cost of reproduction and thus longevity is not always correlated with high fecundity. Parental investment is a key factor in reproductive success since taking better care to offspring is what often will give them a fitness advantage later in life. This includes mate choice and sexual selection as an important factor in reproductive success, which is another reason why reproductive success is different from fitness as individual choices and outcomes are more important than genetic differences. As reproductive success is measured over generations, Longitudinal studies are the preferred study type as they follow a population or an individual over a longer period of time in order to monitor the progression of the individual(s). These long term studies are preferable since they negate the effects of the variation in a single year or breeding season.

Rufous-bellied kookaburra

The rufous-bellied kookaburra (Dacelo gaudichaud), originally known as Gaudichaud’s kookaburra after the French botanist Charles Gaudichaud-Beaupré, is a species of kookaburra which is widely distributed through the forests of lowland New Guinea. It has also been recorded on Saibai Island, Queensland, Australia.

It has a black cap, blue-tinged wings, and a pale rufous belly and tail feathers, but its white bill distinguishes it very clearly from other kookaburras with their black bills. Juveniles, however, have a dark grey bill. Like the blue-winged kookaburra, the sexes can be distinguished by the colour of the tail feathers: blue in males and rufous in females and immature birds. Rufous-bellied kookaburras are smaller than other kookaburra species at around 143 grams (5.0 oz) as against the laughing kookaburra's 335 grams (11.8 oz) and about 28 centimetres (11.0 in) as against the laughing kookaburra’s 46 centimetres (18.1 in). Despite this major size difference, the rufous-bellied kookaburra has been known to form (infertile) hybrids with all other kookaburra species, though available genetic studies suggest it is clearly the most distant of the four.This kookaburra is unusual in that it occupies dense rainforests (as opposed to the open country preferred by other kookaburras) and does not live in cooperative breeding family groups but singly or when breeding in pairs. Rufous-bellied kookaburras can be found in the middle story of the tropical rainforest, where they fly out directly and swiftly from their perch to seize large insects from trees. Despite their direct flight, rufous-bellied kookaburras are capable of very sharp twists and turns around the dense trees that form their habitat. Rufous-bellied kookaburras have been known also to hunt small vertebrates, but do so less frequently than the larger woodland kookaburras, and frequently are mobbed by smaller birds when it preys on their eggs or nestlings. Males are very aggressive in defending their territory, which averages 2 to 2.5 hectares (4.9 to 6.2 acres) in size, and sometimes fight intruders violently.

Like their larger relatives, rufous-bellied kookaburras breed in termite mounds. Breeding usually takes place from May to October, though the young do not disperse fully until February and pairs have never been known to attempt a second brood in one year. Two white eggs are laid, though the actual incubation period is not known.

Seychelles warbler

The Seychelles warbler (Acrocephalus sechellensis), also known as Seychelles brush warbler, is a small songbird found on five granitic and corraline islands in the Seychelles. It is a greenish-brown bird with long legs and a long slender bill. It is primarily found in forested areas on the islands. The Seychelles warbler is a rarity in that it exhibits cooperative breeding, or alloparenting; which means that the monogamous pair is assisted by nonbreeding female helpers.

A few decades ago the Seychelles warbler was on the verge of extinction, with only 26 birds surviving on Cousin Island in 1968. Due to conservation efforts there are more than 2500 of the species alive today with viable populations on Denis, Frégate, Cousine and Aride Islands, as well as Cousin Island [1].

Social monogamy in mammalian species

Monogamous pairing refers to a general relationship between an adult male and an adult female for the purpose of sexual reproduction. It is particularly common in birds, but there are examples of this occurrence in reptiles, invertebrates, fish, amphibians, and mammals.

Tend and befriend

Tend-and-befriend is a behavior exhibited by some animals, including humans, in response to threat. It refers to protection of offspring (tending) and seeking out the social group for mutual defense (befriending). In evolutionary psychology, tend-and-befriend is theorized as having evolved as the typical female response to stress, just as the primary male response was fight-or-flight. The tend-and-befriend theoretical model was originally developed by Dr. Shelley E. Taylor and her research team at the University of California, Los Angeles and first described in a Psychological Review article published in the year 2000.

White-browed scrubwren

The white-browed scrubwren (Sericornis frontalis) is a passerine bird found in coastal areas of Australia. Placed in the family Pardalotidae in the Sibley-Ahlquist taxonomy, this has met with opposition and indeed is now known to be wrong; they rather belong to the independent family Acanthizidae.

It is insectivorous and inhabits undergrowth, from which it rarely ventures, though can be found close to urban areas. It is 11–14 cm (4.3–5.5 in) long and predominantly brown in colour with prominent white brows and pale eyes, though the three individual subspecies vary widely. Found in small groups, it is sedentary and engages in cooperative breeding. The larger Tasmanian scrubwren was formerly considered a subspecies of this species.

White-throated treecreeper

The white-throated treecreeper (Cormobates leucophaea) is an Australian treecreeper found in the forests of eastern Australia. It is unrelated to the northern hemisphere treecreepers. It is a small passerine bird with predominantly brown and white plumage and measuring some 15 cm (6 in) long on average. It is insectivorous, eating mainly ants. Unlike treecreepers of the genus Climacteris, the white-throated treecreeper does not engage in cooperative breeding, and wherever it overlaps with species of that genus, it feeds upon much looser bark besides typically using different trees.

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