Warbler captured on Cousin Island feeding its young (file photo by Cas Eikenaar)
Being the fittest competitor at meal time against your siblings could make you bigger, tougher, live longer and give you greater reproductive prowess, if you’re a Seychelles Warbler that is. This is according to research conducted on the endemic warbler denizens on Cousin Island Special Reserve.
The scientific study titled ‘Consequences of sibling rivalry vary across life in a passerine bird’ was published in November 2016 in Behavioral Ecology, the official journal of the International Society for Behavioral Ecology (ISBE). A team of researchers from the Seychelles Warbler Group outlined how they put the theory to the test by comparing warblers who had been raised on their own against those that had one or more siblings.
The Seychelles Warbler Group is part of a long term partnership between Nature Seychelles and researchers from the Universities of East Anglia and Sheffield in the UK, and the University of Groningen in the Netherlands. The researchers involved in this particular study were Kat Bebbington, Sjouke Kingma, Eleanor Fairfield, Lewis Spurgin, Jan Komdeur, and David Richardson.
Certainly, there have been many analyses by other experts to ascertain the cost of familial rivalry in other animal species, which have shown that despite the parents’ efforts, the higher the number of youngling, the less there is to go around; and the less there is to eat, the lower the growth rate, body size and development of the immune system, all of which can affect survival later in life.
This juvenile warbler wil most likely face stiff competition later in life from another who was not raised on its own (file photo by Martijn Hammers)
In fact, such contest for resources at an early age in some species may lead individuals to feel compelled to commit siblicide (killing of a sibling).
However, the theatrics in Seychelles Warbler society are not quite as dramatic. But there is indication that the most competitive individual tends to be bigger and have a higher survival rate, and in the long term increased reproductive potential. Interestingly, stronger competitors “had a longer breeding tenure and life span than single offspring” that were raised without the trouble, as it were, of competition.
The research was based on data collected between 1995 and 2014 of the Seychelles Warbler population on Cousin Island which is managed by Nature Seychelles (BirdLife in Seychelles). Saving the Seychelles Warbler from extinction is the reason the island was bought in 1968 and restored from a coconut plantation. Over the years extensive data on this bird has been collected for research and of course, conservation purposes.
In fact, each individual bird can be identified by its unique (British Trust for Ornithology) ring and a combination of colour rings. Apart from identification, information gathered over the years from monitoring work is a valuable ‘pot’ for future research.
In conclusion the report states “We suggest that comparisons of individuals raised with and without sibling competition, combined with detailed monitoring of individuals throughout life, will be instrumental in future studies of sibling rivalry, evolution of parental investment, and individual reproductive strategies in wild systems.”