Older and grumpier: Aging sparrows have fewer friends

Amazing stuff! But how much is due to effect of natural changes in demography (older ones dying off)?

"... Researchers have tracked every house sparrow on tiny Lundy Island in the U.K. from egg to death since 2000, so they know exactly how old each animal is. From 2013 to 2017, they also collected detailed social data by noting interactions between individuals at video-monitored bird feeders. In all, they tallied more than 1600 observations of 615 different individuals, finding that the number of “friends” (defined as individuals a given bird is often observed with) decreased with age. Not only did old birds lose touch with old friends, they formed fewer new social connections. ..."

From the abstract:

"Humans become more selective with whom they spend their time, and as a result, the social networks of older humans are smaller than those of younger ones. In non-human animals, processes such as competition and opportunity can result in patterns of declining sociality with age. While there is support for declining sociality with age in mammals, evidence from wild bird populations is lacking. Here, we test whether sociality declines with age in a wild, insular bird population, where we know the exact ages of individuals. Using 6 years of sociality data, we find that as birds aged, their degree and betweenness decreased. The number of same-age birds still alive also decreased with age. Our results suggest that a longitudinal change in sociality with age may be, in part, an emergent effect of natural changes in demography. This highlights the need to investigate the changing costs and benefits of sociality across a lifetime."

ScienceAdvisor

Not so social in old age: demography as one driver of decreasing sociality (open access)

Figure 1.
(a) The number of repeated observations of individuals.
(b) The ages of Lundy house sparrows (y-axis, in years) in relation to the percentage of fledged individuals of their own cohort that were still alive (x-axis), 2013−2017.