Birds of a feather flock together: Insights into starling murmuration behaviour revealed using citizen science

Abstract

Pre-roost murmuration displays by European starlings Sturnus vulgaris are a spectacular example of collective animal behaviour. To date, empirical research has focussed largely on flock movement and biomechanics whereas research on possible causal mechanisms that affect flock size and murmuration duration has been limited and restricted to a small number of sites. Possible explanations for this behaviour include reducing predation through the dilution, detection or predator confusion effects (the "safer together" hypotheses) or recruiting more birds to create larger (warmer) roosts (the "warmer together" hypothesis). We collected data on size, duration, habitat, temperature and predators from >3,000 murmurations using citizen science. Sightings were submitted from 23 countries but UK records predominated. Murmurations occurred across a range of habitats but there was no association between habitat and size/duration. Size increased significantly from October to early February, followed by a decrease until the end of the season in March (overall mean 30,082 birds; maximum 750,000 birds). Mean duration was 26 minutes (± 44 seconds SEM). Displays were longest at the start/end of the season, probably due to a significant positive relationship with day length. Birds of prey were recorded at 29.6% of murmurations. The presence of predators including harrier Circus, peregrine Falco peregrinus, and sparrowhawk Accipiter nisus was positively correlated with murmuration size (R2 = 0.401) and duration (R2 = 0.258), especially when these species were flying near to, or actively engaging with, starlings. Temperature was negatively correlated with duration but the effect was much weaker than that of day length. When predators were present, murmurations were statistically more likely to end with all birds going down en masse to roost rather than dispersing from the site. Our findings suggest that starling murmurations are primarily an anti-predator adaptation rather than being undertaken to attract larger numbers of individuals to increase roost warmth.

Fig 1

Reported starling murmurations: (a) = international distribution (; (b) UK basic distribution; (c) = UK distribution showing number of records; (d) = UK distribution showing mean size of murmuration. All base maps from Natural Earth (freely available in the Public Domain); all starling data from Starling Survey run by authors and freely available–see Data Availability Statement. Maps created using QGIS under CC BY.

Fig 2. Number of murmurations associated with different landscapes (terrestrial, anthropogenic, aquatic) and different habitats with those landscapes based on data from survey year one (2014/15); n = 1,293.

Fig 3

Temporal patterns in: (a) number of murmurations (n = 1,644); (b) mean number of birds per confirmed murmuration (n = 1,293); and (c) mean duration of murmuration only including records where the end of the murmuration event was recorded (n = 553). All data based on data from survey year one (2014/15); more details on sample sizes are given in Table 1. Dotted lines show annual means. Error bars show standard error.

Fig 4. Relationship between murmuration duration (weekly mean duration in minutes) and day length in 2014/15 based on records where the end of the murmuration event was recorded (N = 553).

Fig 5. Number of murmurations associated with potential predators based on data from survey year two (2015/16); n = 1,134.