Cooperation & Helping
Cooperative Breeding in Vertebrates
Young often require large amounts of adult care
Care is usually provided by female alone or by both male and female
Among some rodents, mammalian carnivores, & more than 300 species of
birds, additional adults (alloparents or helpers) play a role in raising
when more than two adults provide care
Helper-at-the-den/nest - auxiliary (non-breeding) adult(s) contribute physically,
but not genetically, to rearing of young
Communal breeding systems:
parentage of offspring is shared
several males have chance to father offspring & several females have
chance of having young
young are cared for communally
Examples of helper-at-the-den/nest breeding systems:
Examples of communal breeders:
Monadjem, A. Cooperative breeding in southern African
passerines and brood parasitism: Is there a relationship? South African
Journal of Science 92:295.
In order for an obligate avian brood-parasitic species
to lay eggs, the species must first locate the nest of the host species.
Tests have been done to see if cooperative breeders are more easily detected
and attract brood parasites.
Results -- Out of 187 passerine species with 21 south
African bird species as brood parasites:
Conclusion -- The detectability of the nest only plays a
minor role in the passarine species. Species with easily detectable
nests but with good egg discrimination, are poor hosts to the brood parasite.
This may be the reason for the lack of association between breeding system
and brood parasitism.
number of hosts: non cooperative (165)
number of hosts: facultatively cooperative (7)
number of hosts: obligately cooperative (15)
Submitted by Andrea Pinkston
Do helpers really help? Is there any correlation between the presence
of helpers and the production of young?
Silver-backed Jackal (Moehlman 1979)
Bee-eater (Emlen 1981)
Helpers may contribute to increased survival of young by providing:
greater protection from predators
more food for young than could be provided by parents alone
(feeding rate = no. of regurgitations and/or 'nurses'
provided to litter of pups/hour)
(feeding rate = total number of insects brought to young
per hour when nestlings were 14 - 22 days old)
Experimental evidence - Brown et al. (1982):
selected 20 groups of babblers with about the same number of individuals
and equivalent territories
removed all but 1 helper from 9 breeding groups
11 control groups averaged 7 members (ranging from 6 to 8)
Helpers DO help in babblers & in many other species, and breeders
are the beneficiaries. But, what about the helpers? Do they also benefit
or would they be better off leaving the group?
Why don't helpers breed on their own?
Koenig (1981) examined productivity data for 15 species of avian cooperative
Reproductive success of breeding pairs increased with group size in 13
species, but there was no consistent correlation between per capita reproductive
success and group size (i.e., increased group size = lower fitness per
Conclusion - helpers would often do better to initiate their own breeding
Two primary reasons why animals might live & reproduce in social groups
larger than pairs:
benefits of group living
individuals might be 'forced' to remain in groups because of ecological
or other constraints
Most work support the 'constraints model':
helpers tend to have reduced fitness, suggesting they 'should' leave and
form their own group or breeding pair
several 'constraints' could induce helpers to remain in a group despite
risks associated with dispersal
low probability of obtaining a mate
low probability of obtaining a vacant territory
low probability of successfully reproducing once established
the two 'reasons' (benefits of group living vs. constraints) would likely
produce different types of groups:
if groups result from the benefits of group living, then groups should
form regardless of the relationships between individuals
if groups are the result of 'constraints', then groups should consist of
close relatives because they form by retention of young
groups for most, if not all, cooperative breeders consist of close relatives
Types of constraining factors:
risks of dispersal
probability of survival in a familiar breeding area is higher than in unoccupied,
marginal areas available to dispersers
short-term cost of postponing dispersal and reproduction may be compensated
by improved longevity & higher lifetime reproductive success
shortage of territory openings or other necessary resources
many cooperative breeders are permanently territorial species that:
inhabit stable or regularly predictable environments
have specific ecological requirements such that the availability of suitable
habitat is restricted &, if so:
the option of breeding independently may be limited (because territories
individuals may have to wait until they attain sufficient age, experience,
or status to obtain & defend a territory
the availability of territories seems to be a common ecological constraint
among cooperatively-breeding birds, e.g.:
& similar constraints may occur in some mammals, e.g., silver-backed
jackal, wild dogs, & gray wolves
shortage of mates
skewed sex ratios (with more males than females) have been reported in
some cooperatively breeding birds:
prohibitive costs of independent reproduction
cooperative breeders may occupy variable & unpredictable environments
that make successful reproduction more difficult. If so, young may be better
off remaining in natal groups.
Test of the contraints model:
(Ecological constraint = log of total rainfall occurring
in the month preceding breeding)
Why do helpers help?
Lifetime fitness of helpers must be equal to or greater than the fitness
of individuals that attempt early dispersal and breeding
How can helping enhance fitness?:
breeding experience - if reproductive success of experienced breeders is
greater than for inexperienced breeders, then young may benefit from helping
by gaining parental experience
inheritance of the parental territory
non-breeders remaining in natal group may eventually inherit all or part
of the parental territory
may be very important in species where territories are a primary ecological
reported in a variety of species, including jackals, wolves, lions, &
increased inclusive fitness (as a result of helping kin)
Helping Behavior in Birds:
Trombino (1999) - Interspecific and intraspecific helping
behavior within Sapsuckers
Interspecific and intraspecific helping behavior have been
previously recorded in birds, but are uncommon and rare (2.4% of bird species
exhibit intraspecific helping behavior).
Interspecific - Red-breasted,
hybrid (Red-breasted X Red-naped), and Williamson’s
Sapsuckers fed nestlings of different species.
Intraspecific - Individuals of the same species
(Red-breasted Sapsucker) fed nestlings that were not there own.
Helping behavior was defined as when more than two adults
were seen feeding young.
Interspecific helping occurred at 2 nests:
adults at first nest (female hybrid, Red-naped female, and
adults at second nest (one male and female Red-breasted Sapsucker
and Williamson’s Sapsucker)
Intraspecific helping occurred at one nest:
three adult Red-breasted Sapsuckers provisioned young (sexes
Contributed by Ben Sutter
In theory, helping to feed another species should not have
an evolutionary benefit. However, unmated males may benefit by gaining
experience in feeding young, which may enhance the probability of pairing
in the next breeding season. Given that helping behavior in sapsuckers
is rare, the most likely explanation is that adult birds are responding
to feeding stimulus (begging by young).
Christman and Steven (1998) – Adult Bridled
Titmice (Baeolophus wollweberi) were assisted by individuals
of the same species, which were hatching year and after hatching year birds.
Helpers were present at two nests:
First nest (hatching year helper - male) - out of 103
feedings: 38% by male, 38% be female, and 24% by helper.
Second nest (after hatching year helpers – male and
unkown) - exact feedings were unknown by four individuals; helpers feed
and gave alarm calls
Contributed by Ben Sutter
Interspecific helping behavior can occur frequently in Bridled
Titmice, but helping is rare within the tit family (Paridae).
When it does occur, phylogeny appears to influence cooperative
breeding in titmice.
Bridled Titmice exhibit behavioral characteristics of cooperative
species including stable flocks and group territories in non-breeding season.
Taxonomic isolation may explain the presence of helping behavior
in Bridled Titmice and not in other parids.
The cause of apparent different age classes of helpers remains
When do helpers become communal reproductives?
Why do helpers not always reproduce communally within
in helper-at-the-den/nest systems, dominant breeding individuals typically
realize greater fitness than subordinate helpers
in communal breeding systems, several individuals of one or both sex(es)
are reproductives & fitness benefits, as well as parental care costs,
are more equally distributed among group members
constraints typically keep auxiliaries (helpers) in the area
helpers benefit in terms of access to resources (and other benefits of
dominant breeders may 'extract fitness' from helpers and, in return, they
allow helpers to remain in the area
constraints may be relaxed and/or auxiliaries may be older (with better
'status' within the group) &, as a result, breeders may have less leverage
with somewhat less leverage, breeders may still be able to 'manipulate'
auxiliaries to induce them to remain as helpers (e.g., disruption of breeding
opportunities of auxiliaries by harassment or even destroying nests &
eggs or killing pups)
reported in species such as Acorn Woodpeckers, wolves, and wild dogs
with a greater reduction in leverage, interference strategies may become
more costly in terms of time, energy, & risks of retaliation. If fitness
gain associated with increased group size is sufficiently great, breeders
may yield a portion of their fitness to auxiliaries.
Mendres, K A., and F.B. M. De Waal. 2000.
Capuchins do cooperate: the advantage of an intuitive task. Animal
Behaviour 60: 523-529.
Most studies have examined ultimate reasons for cooperation,
these researchers looked at a proximate reason (cognitive mechanism) for
cooperation in Capuchin monkeys (Cebus apella). In the wild
and captivity, these monkeys will share food with other individuals (both
infants and adults). So, they tested the Capuchin’s cooperation in
Created a chamber with two rooms (one individual per room)
divided by mesh and a counter-weighted tray attached by bars. Food
bowls were placed on the bars but only one bowl contained food.
Cooperation Test (COT)- tray heavy enough that
both individuals needed to pull for Ind. 1 to get food
Solitary Effort Test (SET) – bar to Ind. 2 removed and tray
light enough for Ind. 1 to pull food alone.
Obstructed View Test (OVT) – Mesh replaced with opaque panel
so individuals can’t see each other, both needed to pull tray
Unrestricted Cooperation Test (UCT)- Ind.2 able to go to
group cage but Ind.1 needs help to move tray for food
Conclusions -- Capuchins communicate with each other (like
glancing) and cooperate in order to acquire food – even if only one individual
would get the food. When an individual could acquire food alone,
he/she would not solicit help from the partner.
OVT had less success than COT although pulled as often (less
Ind.1 in COT glanced at partner more often than in SET
Ind.1 pulled more often in UCT when partner present
Contributed by Heather Brace
|Social factors determine cooperation in marmosets
(Werdenich and Huber 2002) --Marmosets
(Callithrix jacchus) were trained to pull a handle to reach a food
container. In the first phase (dyadic training) each partner could
solve the task alone, while the second phase (cooperation test) used a
modified apparatus whose successful handling required the assignment of
roles and synchrony of actions.
Each monkey was paired with both a cagemate
of the same sex and of the opposite sex as well as with a dominant and
subordinate partner. Dyadic Training: The “producer” was the
individual who made the food accessible by pulling the string, whereas
the “scrounger” needed only to grasp the reward. Cooperation Test:
One partner had to pull the string while the second partner could easily
obtain a piece of food by pushing away the lid as soon as the bowl was
close to the wire mesh.
Results: Dyadic Training: All subjects except one
took different roles with different partners. Fourteen of the 16
dyads showed a clear dominance relationship.
Cooperation Ability: All eight subjects showed
successful cooperative behavior.
Factors Causing Cooperation: The four dyads that
were successful in the cooperation test were those in which the subordinate
partner was the producer and the dominant partner was the scrounger in
the dyadic training. Dominant partners of cooperative dyads did not
obtain more rewards than subordinate ones.
--- Contributed by Ryan Dunbar
Photo source: http://www.zoo.ru/Moscow/monk_e8.htm
Brown, J.L. 1974. Alternate routes to sociality in jays
- with a theory for the evolution of altruism and communal breeding. American
Brown, J.L., E.R. Brown, S.D. Brown, & D.D. Dow. 1982.
Helpers: effects of experimental removal on reproductive success. Science
Christman, B.J. and G. Steven. 1998. Unambiguous evidence
of helping at the nest in Bridled Titmice. Wilson Bull. 110: 567-569.
Emlen, S.T. 1981. Altruism, kinship, and reciprocity in
the White-fronted Bee-eater. Pp. 217-230 in Natural Selection and Social
Behavior (R. D. Alexander and D. Tinkle, eds). Chiron Press.
Emlen, S.T. 1982. The evolution of helping. I. An ecological
constraints model. American Naturalist 119:29-39.
Koenig, W.D. 1981. Reproductive success, group size, and
the evolution of cooperative breeding in the Acorn Woodpecker. Am. Nat.
Moehlman, P.D. 1979. Jackal helpers and pup survival.
Rood, J.P. 1980. Mating relationships and breeding suppression
in Dwarf Mongoose. Anim. Behav. 28:143-150.
Trobino, T. 1999. Helping behavior within sapsuckers (Sphyrapicus
spp.). Wilson Bull. 112: 273-275.
Vehrencamp, S.L. 1978. The adaptive significance of communal
nesting in Groove-billed Anis (Crotophaga sulcirostris). Behav.
Ecol. Sociobiol. 41:1-33.
Werdenich, D. and L. Huber. 2002. Social factors determine
cooperation in marmosets. Animal Behaviour 64:771-781.
Woolfenden, G.E. and J.W. Fitzpatrick. 1984. The Florida
Scrub Jay: demography of a cooperative-breeding bird. Princeton Univ. Press,
breeding in birds: a comparative test of the life history hypothesis
Shows the Queen of Beasts Breeds Democratically
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