Cooperative Breeding

JodyLee Estrada Duek, Ph.D.With assistance from Dr. Gary Ritchison

http://people.eku.edu/ritchisong/matingsystems.html

Groove-billed ani

Cooperative Breeding 1• "Cooperative" or "communal" breeding occurs when more than two

birds of the same species provide care in rearing the young from one nest.

• About 3 percent (approximately 300 species) of bird species worldwide are cooperative breeders.

• There are two types of cooperative arrangements: 1. those in which mature nonbreeders ("helpers-at-the-nest" or "auxiliaries")

help protect and rear the young, but are not parents of any of them, 2. those where there is some degree of shared parentage of offspring.

• Cooperative breeders may exhibit shared maternity, shared paternity, or both.

Cooperative Breeding 2• 'helpers' provide parental care for young that are not their own • care given usually includes food, but other types of care are also

common, such as territorial defense, nest construction, incubation, and defense from predators

• observed in over 220 species of birds • occurs most frequently in the tropics & Australia; less common in

Europe & North America

Cooperative Breeding 3

• The best-studied North American cooperative breeders, Scrub-Jay, Gray-breasted (Mexican) Jay, Groove-billed Ani, Acorn Woodpecker, differ in the details of their breeding biology.

• Scrub jays in Florida represent a group of populations that probably were once in contact with the widespread western populations but are now totally isolated.

• Only in Florida are Scrub jays cooperative breeders, and there they reside in permanent, group-defended territories

• Ornithologists Woolfenden and Fitzpatrick found groups consist of a permanently bonded monogamous pair and one to six helpers, generally the pair's offspring

• Half the territories are occupied by pairs without helpers; most others have one or two• Although pairing and breeding can occur after one year as a helper, birds often spend

several years as nonbreeding auxiliaries• Males may remain up to six years; females usually disperse and pair after one or two years• Helpers participate in all nonsexual activities except nest construction, egg laying, and

incubation. • Pairs with helpers are more successful -- they fledge one and a half times more young than

pairs without helpers.

Cooperative breeders’ characteristics: • low breeding rates • high adult survival • limited dispersal • deferred maturity (may not breed until at least 2 years old)

Gray-breasted (Mexican) jay

Cooperative breeding in suboscines

• In the 1097 species of New World suboscines, (in general, any bird of the suborders Eurylaimi, Tyranni, and Menurae of the order Passeriformes - perching birds, or passerines - as distinguished from an oscine, or songbird. The term suboscine implies more primitive in anatomy and behaviour than the oscines) cooperative breeding is rare, inferred in just 16 species.

Cooperative breeding in oscines

• By contrast, a larger proportion of oscines are cooperative breeders (577 of 4456 species; 13%). It is unlikely that there is a simple ecological or life history explanation for this difference. Both clades have diversified into an enormous range of niches and show overlapping variation in life history. The low prevalence in suboscines is unlikely to be a result of the environment they occupy.

• Several oscine taxa have primarily radiated in the Neotropics and hence overlap the range of the New World suboscines. Many of these have a high incidence of cooperation (e.g., New World jays, mimids, emberizids, icterids and wrens).

Environmental Variability Drives the Evolution of Cooperative Breeding in Vertebrates, in Birds

• Many vertebrates breed in cooperative groups in which more than two members provide care for young.

• Studies of cooperative breeding behavior within species have long highlighted the importance of environmental factors in mediating the paradox of why some such individuals delay independent breeding to help raise the offspring of others.

• In contrast, studies involving comparisons among species have not shown a similarly clear evolutionary-scale relationship between the interspecific incidence of cooperative breeding and any environmental factors.

• Rubenstein and Lovette 2007 used a phylogenetically controlled comparative analysis of a complete, socially diverse group of birds — 45 species of African starlings — to show that cooperative breeding is positively associated with living in semiarid savanna habitats and with temporal variability in rainfall.

• Savanna habitats are not only highly seasonal, but also temporally variable and unpredictable, and this temporal variability directly influences individual reproductive decisions in starlings and helps explain interspecific patterns of sociality.

• Cooperative breeding is adaptive in temporally variable environments because it allows for some reproduction in harsh years and sustained breeding during benign years.

• This “temporal variability” hypothesis might help explain the phylogenetic and geographic concentrations of cooperatively breeding vertebrates in savanna-like habitats and other temporally variable environments worldwide.

Superb starling• A Superb Starling, a cooperative breeding savanna dweller abundant

throughout northeast Africa (Dustin R. Rubenstein photo).

Possible explanations

Costs or Benefits to Helpers

Costs or Benefits to Breeders Explanation

decrease in fitness increase in fitness helpers are altruistic

increase in fitness decrease in fitness helpers are selfish

increase in fitness increase in fitness both helpers & breeders benefit

A 'test' of these explanations: 1

• Gray-crowned Babblers: Brown & Brown (1981) removed helpers from some groups and studied breeding success of 1. large groups (no helpers removed)2. experimentally-reduced groups3. natural small groups

• Possible outcomes: – if helpers increase breeding success, removal would decrease breeding

success to a level comparable to natural small groups – if helpers decrease breeding success, removal would increase breeding

success – if helpers are 'neutral', removal would not influence breeding success

Gray-crowned babbler

A 'test' of these explanations: 2• Results:

– Large groups averaged 2.4 young/group – Reduced groups averaged 0.8 young/group

• Conclusion: Helpers do help but might be able to do better on their own (& this also appears to be true in Scrub Jays ).

Scrub jayPhoto: Ray Wilson

Cactus wrens• Live in family groups

with DR• Siblings stay in family

territory but do not assist at the nest

• Adults build a series of nests during the year, with sequential clutches

• Each clutch takes over one or more recent nests as parents move to a new nest, begin again

Cactus wren, Tucson

Why do helpers 'stay at home' & help?

• Young birds delay dispersal & reproduction : – dispersal is risky

• unfamiliar habitats with unpredictable food supplies • increased predation risk

– available habitat saturated (all territories occupied) – only the 'home' territory may have essential resources. For example:

• acorn storage sites for Acorn Woodpeckers (photo) • cavities for Red-cockaded Woodpeckers

– they may not have the skills needed to breed on their own, e.g., skills needed to acquire & defend a territory or to care for young

– harsh conditions (such as drought) may make successful breeding unlikely for birds on their own (that is, without helpers)

Acorn woodpecker granary

Acorn Woodpeckers 1• Long-term studies of Acorn Woodpeckers have been conducted by a

succession of ornithologists, including M. H. and B. R. MacRoberts, Koenig, Mumme, and Pitelka in central coastal California

• There Acorn Woodpecker groups are composed of up to 15 members whose territories are based on the defense and maintenance of granaries in which they store acorns

• Groups consist largely of siblings, their cousins, and their parents • Some of the sexually mature birds are nonbreeding helpers • Within each group, up to four males may mate with one (or

occasionally two) females, and all eggs are laid in a single nest• Paternity and sometimes maternity of communal clutch is shared

Acorn Woodpeckers 2• Per capita reproductive success generally increases with group size

up to 7 or 8 members, and then declines• Clutches produced by two females are somewhat less successful than

those of single females due to behavioral interference between the two females and some egg tossing

• Although there is some geographic variation in the size of groups and other aspects of the Acorn Woodpecker system, it breeds cooperatively throughout its range

Acorn Woodpeckerhttp://video.google.com/videoplay?docid=6656661551287167267&q=acorn+woodpecker&total=26&start=0&num=10&so=0&type=search&plindex=4

• Cooperative strategies include storage of acorns for future use

1. ecological constraint; Emlen (1982): hypothesis DR response to constraints on dispersal options. Habitat saturation or environmental variation leads to lack of high-quality openings so offspring delay dispersal

strong point: manipulation of constraints explains dispersal patterns within some speciesweak point: most species face some constraints and do not delay dispersal; does not explain interspecific variation

2. life-history; Arnold & Owens (1998): hypothesis DR has a phylogenetic component and is more frequent in long-lived species -- they occupy territories longer, leading to habitat saturation and preventing younger individuals from obtaining breeding positions

strong point: partly explains phylogenetic pattern of DR and attempts to reconcile cooperation with life-history correlatesweak point: majority of long-lived species are not cooperative; in practice proposes same mechanism as the EC hypothesis and hence has same weak points

3. prolonged investment: parental nepotism; Brown (1987); Ekman et al. (2001a): hypothesis: offspring gain direct fitness benefits from prolonged association with parents due to nepotistic parental behaviours that improve offspring fitness

strong point: explains why offspring should prefer to wait for the onset of reproduction at home; provides basis to understand family formation. brings together parental investment and life-history characteristicsweak point: neglects the role of life-history characteristics on reproductive decisions of offspring; does not entirely explain interspecific variation

Major hypotheses for DR

Proposed pathway leading to family formation in birds 1

• Effects of life history and environmental factors on parental decisions are illustrated by the grey arrows

• Effects on offspring decisions are shown by the black arrows.

• The environmental factors are shown in boxes. • The directions of the relationships between

traits or factors are illustrated by 'plus' for positive correlations and 'minus' for negative correlations. + -

Red-cockaded woodpecker

Proposed pathway leading to family formation in birds 2: Conclusions

• Species with high survival tend to start breeding later in life and can invest more in offspring

• These two factors combined can cause offspring to delay dispersal, leading to the formation of families

• Environmental factors such as good breeding conditions promote dispersal

• Resource availability allows parents to invest more in offspring without incurring strong costs

• However, parents should only prolong investment in offspring if this increases offspring survival prospects substantially without compromising parents’ own survival

• Thus, there should not be parental investment when offspring survival is too low or too high

Life history and the evolution of family living in birds // Rita Covas and Michael Griesser

Florida Scrub-Jays + Western Scrub-Jays

• Florida Scrub-Jays are largely restricted to the scattered and now much reduced oak scrub habitat; reproductive success outside of oak scrub is very poor.

• All available habitat is occupied, and populations appear to be stable from year to year, which means young birds are unlikely to find vacant space to set up territories of their own.

• In contrast, Western Scrub-Jays generally are not space-limited, and the probability of a young bird leaving home and finding a territory in which to breed is high.

Gray-breasted Jay• Like the Florida Scrub-Jay, the closely related Gray-breasted Jay of

the southwestern U.S. lives in permanent group-defended territories, and breeding adults are monogamous

• Studies by ethologist Jerram Brown and colleagues have shown the cooperative system of this species is more complex than that of its southeastern relatives in several ways

• Gray-breasted Jay groups are much larger, ranging from 8 to 18 individuals; thus, they usually include offspring from more than just the preceding year.

• Within each group, two and sometimes three breeding pairs nest separately but simultaneously each season, and some interference among them often occurs

• Interference involves the theft of nest-lining materials, but can include the tossing of eggs from nests by females of rival nests

• Although the laying female does all the incubating, she is fed by her mate and by auxiliaries.

• Nestlings receive more than half of their feedings from auxiliaries.

Life history and the evolution of family living in birds 1

(article)• why do some bird species live in family groups? important unanswered question• Families arise when young delay onset of independent reproduction and remain

with parents beyond independence• Explanations have focused on dispersal constraints, such as absence of high-quality

breeding openings • However, although constraints successfully explain within-population dispersal

decisions, they fail as an ultimate explanation for variation in family formation across species.

• Most family-living species are long-lived and recent life-history studies demonstrate that delayed reproduction can be adaptive in long-lived species

• Delayed dispersal and reproduction might be an adaptive life-history decision• Covas & Griesser (2007) suggest longevity favors delayed onset of reproduction

and gives parents opportunity of prolonged investment in offspring, an option that is not available for short-lived species.

• Yet, parents should only prolong their investment in offspring if this increases offspring survival and outweighs the fitness cost that parents incur, which is only possible under ecological conditions such as predictable access to resources.

• Covas & Griesser (2007) therefore propose that both life-history and ecological factors play a role in determining the evolution of family living across species.

Life history and the evolution of family living in birds 2• The proposed framework does not exclude the possibility that family

associations might arise through different pathways• Long-tailed Tits (Aegithalos caudatus) are short-lived and individuals always

attempt to breed in their first year of life, as predicted by life-history theory • In this species, family cohesion is reached through a different pathway• Owing to high nest predation, population density is low, reducing kin

competition and giving offspring the option to delay dispersal and remain associated with their parents throughout their first winter

• Then, they disperse and attempt to reproduce independently, but return to the parental territory to help their relatives if breeding attempt fails

• In this species, family living seems unrelated to life-history characteristics and appears linked to environmental factors that allow family structure to be kept after breeding season and to nesting in close spatial association

• http://www.youtube.com/watch?v=jB0Ia65vngo long-tailed tits

Groove-billed Ani 1

• Although the Groove-billed Ani breeds in southern Texas, our knowledge of its breeding biology comes from the work of sociobiologist Sandra Vehrencamp who worked in Costa Rica.

• The groups defending permanent territories consist of one to four monogamous breeding pairs that may include an unpaired helper.

• All members of the group participate in building a single nest into which all females lay their eggs

• Incubation and care of the young are shared by all• Beyond a certain clutch size, some eggs tend to be buried and fail to

receive proper incubation, leading to decreased probability of any given egg hatching.

Groove-billed Ani 2• Unlike the "cooperative" breeders that they appear to be, female

anis engage in behaviors that increase the probability of their own eggs being the successful ones in the communal clutch

• The most effective of these behaviors is the tossing of other females' eggs from the nest

• In spite of the increased competition and conflict, multipair groups manage to fledge more young per individual than do single pairs in similar habitats

Why Cooperative Breeding?• Why has evolution produced cooperative breeding systems? Initial hypotheses were based

on kin selection (seemingly "selfless" behavior like helping at the nest being favored because it increases the reproductive success of relatives genetically similar to the helper) or on maximizing of reproductive output. As more cooperatively breeding species have been examined worldwide, these explanations generally have not been supported. Instead, cooperative systems appear to arise when environmental constraints force birds into breeding groups because the opportunities for younger birds to breed independently are severely limited. Limitations may include a shortage of territory openings because higher quality habitats are saturated with established breeders; a shortage of sexual partners (generally females), indicated by the skewed sex ratios that are common in groups; and unpredictable availability of resources, which could make it too risky for individual pairs to commit themselves to reproduce in any given year. That cooperative breeding is a common strategy in arid and semiarid portions of Africa and Australia lends strong support to this line of reasoning. Cooperative breeding may be viewed primarily as a means by which young adults put off the start of their own breeding in order to maximize their lifetime reproductive output, and in the process occasionally promote genes identical with their own via kin selection.

Not always complete cooperation• Acorn woodpecker females replacement story• http://video.google.com/videoplay?docid=6130761313069739265

• Gray-crowned babbler• http://video.google.com/videoplay?docid=5020960287597912571&q=bird+

%2B+babblers&total=23&start=0&num=10&so=0&type=search&plindex=4