Calves as social hubs: dynamics of the social network within sperm whale units. Gero, S., Gordon, J., & Whitehead, H. Proceedings of the Royal Society of London B: Biological Sciences, 280(1763):20131113, The Royal Society, 2013.
Calves as social hubs: dynamics of the social network within sperm whale units [link]Paper  doi  abstract   bibtex   
It is hypothesized that the primary function of permanent social relationships among female sperm whales (Physeter macrocephalus) is to provide allomothers for calves at the surface while mothers make foraging dives. In order to investigate how reciprocity of allocare within units of sperm whales facilitates group living, we constructed weighted social networks based on yearly matrices of associations (2005\textendash2010) and correlated them across years, through changes in age and social role, to study changes in social relationships within seven sperm whale units. Pairs of association matrices from sequential years showed a greater positive correlation than expected by chance, but as the time lag increased, the correlation coefficients decreased. Over all units considered, calves had high values for all measured network statistics, while mothers had intermediate values for most of the measures, but high values for connectedness and affinity. Mothers showed sharp drops in strength and connectedness in the first year of their new calves\textquoteright lives. These broad patterns appear to be consistent across units. Calves appeared to be significant nodes in the network of the social unit, and thus provide quantitative support for the theory in which communal care acts as the evolutionary force behind group formation in this species.
@ARTICLE{Gero2013,
  author = {Gero, Shane and Gordon, Jonathan and Whitehead, Hal},
  title = {Calves as social hubs: dynamics of the social network within sperm
	whale units},
  journal = {Proceedings of the Royal Society of London B: Biological Sciences},
  year = {2013},
  volume = {280},
  pages = {20131113},
  number = {1763},
  abstract = {It is hypothesized that the primary function of permanent social relationships
	among female sperm whales (Physeter macrocephalus) is to provide
	allomothers for calves at the surface while mothers make foraging
	dives. In order to investigate how reciprocity of allocare within
	units of sperm whales facilitates group living, we constructed weighted
	social networks based on yearly matrices of associations (2005{\textendash}2010)
	and correlated them across years, through changes in age and social
	role, to study changes in social relationships within seven sperm
	whale units. Pairs of association matrices from sequential years
	showed a greater positive correlation than expected by chance, but
	as the time lag increased, the correlation coefficients decreased.
	Over all units considered, calves had high values for all measured
	network statistics, while mothers had intermediate values for most
	of the measures, but high values for connectedness and affinity.
	Mothers showed sharp drops in strength and connectedness in the first
	year of their new calves{\textquoteright} lives. These broad patterns
	appear to be consistent across units. Calves appeared to be significant
	nodes in the network of the social unit, and thus provide quantitative
	support for the theory in which communal care acts as the evolutionary
	force behind group formation in this species.},
  doi = {10.1098/rspb.2013.1113},
  eprint = {http://rspb.royalsocietypublishing.org/content/280/1763/20131113.full.pdf},
  file = {:Geroetal2013.pdf:PDF},
  issn = {0962-8452},
  owner = {Tiago Marques},
  publisher = {The Royal Society},
  timestamp = {2016.05.26},
  url = {http://rspb.royalsocietypublishing.org/content/280/1763/20131113}
}

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