Stripe-backed Wren
Encyclopedia
The Stripe-backed Wren, Campylorhynchus nuchalis, is a bird found in the savanna
s of northern Colombia
and central Venezuela
. It lives in dry, riparian woodland, or farmlands, and is found at heights up to 800 m.
The Stripe-backed wren has attracted considerable scientific attention because it is a good example of co-operative breeding. It lives in groups ranging from 2 to 10 adult birds. Of these, only one pair breeds, laying eggs at the beginning of the rainy season (May to September). However all members of the group participate in defence of the territory
, and in feeding the young both in the nest and after fledging. They therefore qualify as helpers at the nest
.
The non-breeding members of the group are usually offspring or siblings of the current breeding parents. After one or two seasons, females normally leave their natal groups and join another nest as helpers, typically in a neighbouring territory. Males, however, usually remain at their natal nest and if they survive will inherit the position of breeding male (though unders some circumstances they too disperse). If the current breeding male dies or is removed, the next oldest male in the group normally takes over its position.
This breeding system may have evolved as a result of kin selection
, but in addition it has been shown by Wiley and Rabenold (1984) that the males' behaviour of "queueing" for the status of breeding male can be an evolutionarily stable strategy
provided some plausible conditions are met. Formally, the situation has the characteristics of a prisoner's dilemma
game that is played repeatedly between the same partners, and in this case "defection" - jumping the queue - would not be advantageous.
Some of the calls of Stripe-backed Wrens show individual variations that are consistent from father to son. This is a potential example of the formation of a dialect in bird song
. The distinctive family calls seem to be used to maintain social contact between members of the co-operatively breeding group.
As would be expected in a species where both sexes share in parental care, the Stripe-backed Wren shows no sexual dimorphism
in appearance.
Savanna
A savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of C4 grasses.Some...
s of northern Colombia
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
and central Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
. It lives in dry, riparian woodland, or farmlands, and is found at heights up to 800 m.
The Stripe-backed wren has attracted considerable scientific attention because it is a good example of co-operative breeding. It lives in groups ranging from 2 to 10 adult birds. Of these, only one pair breeds, laying eggs at the beginning of the rainy season (May to September). However all members of the group participate in defence of the territory
Territory (animal)
In ethology the term territory refers to any sociographical area that an animal of a particular species consistently defends against conspecifics...
, and in feeding the young both in the nest and after fledging. They therefore qualify as helpers at the nest
Helpers at the nest
Helpers at the nest is a term used in behavioural ecology and evolutionary biology to describe a social structure in which juveniles and sexually mature adolescents of either one or both sexes, remain in association with their parents and help them raise subsequent broods or litters, instead of...
.
The non-breeding members of the group are usually offspring or siblings of the current breeding parents. After one or two seasons, females normally leave their natal groups and join another nest as helpers, typically in a neighbouring territory. Males, however, usually remain at their natal nest and if they survive will inherit the position of breeding male (though unders some circumstances they too disperse). If the current breeding male dies or is removed, the next oldest male in the group normally takes over its position.
This breeding system may have evolved as a result of kin selection
Kin selection
Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...
, but in addition it has been shown by Wiley and Rabenold (1984) that the males' behaviour of "queueing" for the status of breeding male can be an evolutionarily stable strategy
Evolutionarily stable strategy
In game theory and behavioural ecology, an evolutionarily stable strategy , which is sometimes also called an evolutionary stable strategy, is a strategy which, if adopted by a population of players, cannot be invaded by any alternative strategy that is initially rare. An ESS is an equilibrium...
provided some plausible conditions are met. Formally, the situation has the characteristics of a prisoner's dilemma
Prisoner's dilemma
The prisoner’s dilemma is a canonical example of a game, analyzed in game theory that shows why two individuals might not cooperate, even if it appears that it is in their best interest to do so. It was originally framed by Merrill Flood and Melvin Dresher working at RAND in 1950. Albert W...
game that is played repeatedly between the same partners, and in this case "defection" - jumping the queue - would not be advantageous.
Some of the calls of Stripe-backed Wrens show individual variations that are consistent from father to son. This is a potential example of the formation of a dialect in bird song
Bird song
Bird vocalization includes both bird calls and bird songs. In non-technical use, bird songs are the bird sounds that are melodious to the human ear. In ornithology and birding, songs are distinguished by function from calls.-Definition:The distinction between songs and calls is based upon...
. The distinctive family calls seem to be used to maintain social contact between members of the co-operatively breeding group.
As would be expected in a species where both sexes share in parental care, the Stripe-backed Wren shows no sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
in appearance.