Editing Helpers at the nest

[[File:Struthidea cinerea lined up.jpg|thumb|Four apostlebirds (''Struthidea cinerea'') of a cooperative breeding group.]]
'''Helpers at the nest''' is a term used in [[behavioural ecology]] and [[evolutionary biology]] to describe a social structure in which [[juvenile (organism)|juveniles]] and [[sexually mature]] [[adolescent]]s of either one or both sexes remain in association with their parents and help them raise subsequent [[offspring|brood]]s or [[Litter (zoology)| litter]]s, instead of dispersing and beginning to reproduce themselves.<ref name=":1" /> This phenomenon was first studied in [[bird]]s where it occurs most frequently, but it is also known in animals from many different groups including [[mammal]]s and [[insect]]s. It is a simple form of [[co-operative breeding]]. The effects of helpers usually amount to a net benefit, however, benefits are not uniformly distributed by all helpers nor across all species that exhibit this behaviour.<ref name=":32">{{Cite journal|last1=Koenig|first1=Walter D.|last2=Walters|first2=Eric L.|last3=Barve|first3=Sahas|date=2019|title=Does Helping-at-the-Nest Help? The Case of the Acorn Woodpecker|journal=Frontiers in Ecology and Evolution|language=English|volume=7|doi=10.3389/fevo.2019.00272|issn=2296-701X|doi-access=free}}</ref> There are multiple proposed explanations for the behaviour, but its variability and broad taxonomic occurrences result in simultaneously plausible theories.<ref name=":6">Dickinson, J. L.; Hatchwell, B. J. (2004) "Fitness consequences of helping" in ''Ecology and evolution of cooperative breeding in birds'' by Walter D. Koenig, Janis L. Dickinson. Cambridge University Press. {{ISBN|978-0-521-53099-6}}</ref>

The term "helper" was coined by [[Alexander Skutch]] in 1935<ref name=":1">{{cite journal|url=http://sora.unm.edu/sites/default/files/journals/auk/Auk/v052n03/p0257-p0273.pdf|author=Skutch, A. F. |year=1935|title=Helpers at the nest|journal=Auk|volume= 52|pages=257–273|issue=3|doi=10.2307/4077738|jstor=4077738 }}</ref> and defined more carefully in 1961 in the avian context as "a bird which assists in the nesting of an individual other than its mate, or feeds or otherwise attends a bird of whatever age which is neither its mate nor its dependent offspring." The term has been criticised as being [[anthropomorphic]], but it remains in use.<ref>{{cite journal|author=Brown, J. L. |year=1978|title=Avian communal breeding systems|journal=Annu. Rev. Ecol. Syst.|volume=9|issue=1 |pages=123–155|doi=10.1146/annurev.es.09.110178.001011|bibcode=1978AnRES...9..123B }}</ref> Other terms used especially in mammals, depending on the specific contexts, are non-maternal (care by other than the mother), alloparental (care by other than the parents), cooperative (care by non-breeding helpers) and communal (care by other breeding females) care.<ref name=":0">{{Cite journal|last1=Rosenbaum|first1=Stacy|last2=Gettler|first2=Lee T.|date=2018|title=With a little help from her friends (and family) part I: the ecology and evolution of non-maternal care in mammals|journal=Physiology & Behavior|language=en|volume=193|issue=Pt A|pages=1–11|doi=10.1016/j.physbeh.2017.12.025|pmid=29933836|s2cid=49380840|doi-access=free}}</ref>

== Examples ==
It occurs in between three and eight percent of bird [[species]] worldwide (estimates vary), but is much more common in [[Australia]] and [[Southern Africa]].<ref>{{cite journal|author1=Jetz, Walter|author2=Rubenstein, Dustin R.|year=2011|title=Environmental Uncertainty and the Global Biogeography of Cooperative Breeding in Birds|url=https://www.researchgate.net/publication/49708773|journal=Current Biology|volume=21|issue=1|pages=72–78|doi=10.1016/j.cub.2010.11.075|pmid=21185192|doi-access=free|bibcode=2011CBio...21...72J }}</ref><ref>McMahon T.A. and Finlayson, B. (1992) ''Global Runoff: Continental Comparisons of Annual Flows and Peak Discharges'', Catena Verlag, {{ISBN|3-923381-27-1}}</ref> Bird species in which this behaviour is found include the [[common moorhen]], the [[house sparrow]], the [[acorn woodpecker]],<ref>{{Cite journal|last1=Koenig|first1=Walter D.|last2=Walters|first2=Eric L.|date=2012-01-01|title=Brooding, provisioning, and compensatory care in the cooperatively breeding acorn woodpecker|journal=Behavioral Ecology|language=en|volume=23|issue=1|pages=181–190|doi=10.1093/beheco/arr172|issn=1465-7279|doi-access=free}}</ref> and the [[apostlebird]]. [[Humans]], [[damaraland mole-rat|damarland mole rats]] and [[Meerkat|meerkats]] are examples of mammals that exhibit this behaviour.<ref name=":0" /> It is also seen in a number of species of bee such as [[carpenter bee]]s (note this is distinct from the behaviour of the [[European honey bee]], where the worker bees are sterile and incapable of reproducing).

== Evolution ==
Three explanations for the occurrence of helpers at the nest have been put forward; they are not mutually exclusive, and in any particular species an investigation of the exact benefits and costs will be needed to see what combination of these factors may have driven the evolution of helping.<ref name=":6" />

*Advantage to the helpers, who may be protected from predation, or gain skills that they will need when they subsequently reproduce, as a result of staying in the parental nest.
*[[Kin selection]]: since subsequent litters or broods from the same parents will be full siblings to the helpers, they are as closely related genetically as their own offspring would be. Helping their parents is therefore as productive for the juveniles as reproducing themselves would be, and if their parents are better able to reproduce, the balance of advantage may be greater.
*Delayed advantage to the helpers, in particular because they stand to inherit their parents' [[territory (animal)|territory]]; this explanation is particularly compelling if suitable territories are in short supply, but requires specific quantitative conditions to be met, favouring a stable queue of potential heirs.<ref>{{cite journal|author1=Wiley, R. H. |author2=Rabenold, K. N. |year=1984 |title=The evolution of cooperative breeding by delayed reciprocity and queuing for favorable social positions |url=http://bilbo.bio.purdue.edu/~www_eco/faculty/rabenold/pdfs/EvoCooperativeBreeding%20by%20delayed%20reciprocity.pdf |journal=Evolution |volume=38 |pages=609–621 |doi=10.2307/2408710 |issue=3 |url-status=dead |archiveurl=https://web.archive.org/web/20100617053619/http://bilbo.bio.purdue.edu/~www_eco/faculty/rabenold/pdfs/EvoCooperativeBreeding%20by%20delayed%20reciprocity.pdf |archivedate=2010-06-17 |jstor=2408710 |pmid=28555990 }}</ref>

== Misconceptions ==
Although it is frequently assumed that helpers are non-breeders, molecular evidence suggests that this may happen, and the term "secondary helper" is sometimes used in this case to indicate helpers that mate with or are not related offspring of the pair being assisted. The term "primary helper" being used for the commoner case of the helper being offspring of the pair and not involved in mating.<ref>Ligon, J. D.; Burt, D. B. (2004) "Evolutionary origins" in ''Ecology and evolution of cooperative breeding in birds'' by Walter D. Koenig, Janis L. Dickinson. Cambridge University Press. {{ISBN|978-0-521-53099-6}}</ref> Extrapair mates are chosen by the females and are these then contribute to the care of the young who may be sired by them.<ref>{{cite journal|title=Female extrapair mate choice in a cooperative breeder: trading sex for help and increasing offspring heterozygosity|author = Rubenstein, DR |doi=10.1098/rspb.2007.0424 |journal=Proceedings of the Royal Society B |year= 2007|volume=274| issue=1620 | pages=1895–1903|pmid=17526455|pmc=2270931 }}</ref>

Juveniles living in association with their parents cannot automatically be regarded as helpers. In a number of species, such as [[Orthonychidae|the logrunners]]<ref>{{cite journal|author=Frith, C.B., Frith, D.W. & Jansen, A. |year=1997|title=The nesting biology of the Chowchilla ''Orthonyx spaldingii'' (Orthonychidae)|doi=10.1071/MU97002|journal=Emu|volume=97|issue=1 |pages=18–30 |bibcode=1997EmuAO..97...18F }}</ref> and the [[Siberian jay]], young remain in the parental territory, but never help feed nestlings. However the delayed advantage explanation for the juveniles' association with their parents can still work in the absence of effective helping, whereas the kin selection explanation cannot.

== Associated effects ==

=== Reproductive success ===
Effects on reproductive success can be but are not always positive, and the strength of that positive correlation varies by species. Sometimes, the energy benefits to breeders, instead of being invested in improving reproductive performance, are used to offset reductions in reproductive performance.<ref name=":12">{{Cite journal|last1=Manica|first1=Lilian Tonelli|last2=Marini|first2=Miguel Ângelo|date=2012-01-01|title=Helpers at the nest of White-banded Tanager Neothraupis fasciata benefit male breeders but do not increase reproductive success|journal=Journal of Ornithology|language=en|volume=153|issue=1|pages=149–159|doi=10.1007/s10336-011-0718-x|bibcode=2012JOrni.153..149M |s2cid=16198295|issn=2193-7206}}</ref> However, in many species, nestling survival rates are increased from helper investments.<ref name=":2">{{Cite journal|last1=Cusick|first1=Jessica A.|last2=de Villa|first2=Miguel|last3=DuVal|first3=Emily H.|last4=Cox|first4=James A.|date=2018-02-23|title=How do helpers help? Helper contributions throughout the nesting cycle in the cooperatively breeding brown-headed nuthatch|journal=Behavioral Ecology and Sociobiology|language=en|volume=72|issue=3|pages=43|doi=10.1007/s00265-018-2470-1|bibcode=2018BEcoS..72...43C |s2cid=4702911|issn=1432-0762}}</ref> Further reproductive success benefits include better quality offspring,<ref name=":2" /> and nestling [[immune response]].<ref>{{Cite journal|last1=Valencia|first1=Juliana|last2=Solís|first2=Elena|last3=Sorci|first3=Gabriele|last4=de la Cruz|first4=Carlos|date=2006-07-01|title=Positive correlation between helpers at nest and nestling immune response in a cooperative breeding bird|journal=Behavioral Ecology and Sociobiology|language=en|volume=60|issue=3|pages=399–404|doi=10.1007/s00265-006-0179-z|bibcode=2006BEcoS..60..399V |s2cid=1898846|issn=1432-0762|hdl=10630/33525|hdl-access=free}}</ref>

=== Parental investment ===
Helpers at the nest can provide advantageous plasticity in the amount of [[Parental investment|investment]] parents need to give to their eggs and chicks. The presence of helpers can be associated with lower investments as the helpers can be depended on to provide certain elements of care and raising.<ref name=":12" /> For example, in the [[Superb fairywren|superb fairy-wren]], nests with helpers present exhibit different average egg sizes than those without helpers.<ref name=":02">{{Cite journal|last1=Langmore|first1=N. E.|last2=Bailey|first2=L. D.|last3=Heinsohn|first3=R. G.|last4=Russell|first4=A. F.|last5=Kilner|first5=R. M.|date=2016-11-30|title=Egg size investment in superb fairy-wrens: helper effects are modulated by climate|journal=Proceedings of the Royal Society B: Biological Sciences|volume=283|issue=1843|pages=20161875|doi=10.1098/rspb.2016.1875|pmc=5136590|pmid=27903872}}</ref> This plasticity can be seen in reference to change in climate conditions. In unfavourable conditions there is a need for female parents to maintain high egg investment, but in favourable conditions, egg investment by mothers declines as helpers can assist with some of the care-load. [[Superb fairywren|Superb fairy-wrens]] with helpers at the nest see average egg sizes increase in dry and hot conditions and decrease in colder conditions compared to nests without helpers.<ref name=":02" />

== Helper variability ==
Generally, helpers provide a net benefit to parents raising offspring, but this benefit is not necessarily distributed uniformly. There can be an uneven distribution of benefits between species, or even between sexes within a species.<ref name=":32" /> Benefits provided by one sex may more heavily fluctuate according to various factors such as food availability. In [[Acorn woodpecker|acorn woodpeckers]], while helpers of both sexes provide relatively the same benefit to reproductive success, male helper behaviour fluctuates. This fluctuation is dependent upon the size of recent acorn crops. Large acorn crops translate to increased behavioural effects from male helpers such as higher rates of granary tending and time spent in the home territory.<ref name=":32" />

== Benefits and consequences for helpers ==
Helpers often also benefit from joining a breeding couple. After unsuccessfully breeding, juveniles may join breeding couples to become helpers. By opting to become helpers while still juveniles and having poor breeding prospects, helpers can benefit from increased survival rates.<ref name=":4">{{Cite journal|last1=McGowan|first1=Andrew|last2=Hatchwell|first2=Ben J.|last3=Woodburn|first3=Richard J. W.|date=2003|title=The effect of helping behaviour on the survival of juvenile and adult long-tailed tits Aegithalos caudatus|journal=Journal of Animal Ecology|language=en|volume=72|issue=3|pages=491–499|doi=10.1046/j.1365-2656.2003.00719.x|s2cid=86529823|issn=1365-2656|doi-access=free|bibcode=2003JAnEc..72..491M }}</ref> A trade-off of this increased survival over non-helper juveniles is that their successful breeding rate after becoming helpers decreases compared to non-helpers.<ref name=":4" />

== See also ==
*[[Alloparenting]]
*[[Altruism (biology)|Altruistic behaviour]]
*[[Ethology]]

==References==
{{reflist}}

[[Category:Behavioral ecology]]
[[Category:Ethology]]
[[Category:Birds]]