One of the gang: social group dynamics in a juvenile passerine bird

Abstract

17Living in groups comes with many potential benefits, especially for juveniles. Naïve individuals may learn 18 how to forage, or avoid predators through group vigilance. Understanding these benefits, however, 19 requires an appreciation of the opportunities juveniles have to associate with (and learn from) others. 20Here we describe social groups in terms of residency, movement, relatedness, and social associations 21 from the perspective of juvenile hihi, a threatened New Zealand passerine bird. Over three years, we 22 identified individuals in groups, their relatedness, and behavioural interactions. Using multistate 23 analysis, we compared movement and residency of adults and juveniles and found that groups were 24 composed predominately of juveniles which remained at group sites for longer than more transient 25 adults. Movement of juveniles between groups did occur but was generally low. There was no evidence 26 that siblings and parents were likely to be seen in groups together. With an initial understanding of group 27 structure, we next asked what characteristics predicted assortment in social network associations. By 28 identifying groups of co-occurring juveniles from time-stamped observations of individual hihi and 29 building a social network, we found that juveniles were most likely to associate with other juveniles. 30Associations were also predominantly based on locations where hihi spent the most time, reflecting 31 limited movement among separate groups. We suggest groups are best described as "gangs" where 32 young hihi have little interaction with adults. These spatially-separated groups of juveniles may have 33 consequences for social information use during the first few months of independence in young birds. 77between juveniles only, interactions can include "social play" (documented in species such as ravens 78 (Heinrich and Smolker, 1998)), where at least two individuals engage in a reciprocated behaviour and 79 alternate between roles, and potentially share information (Diamond and Bond, 2003). However, the 80 presence of many naïve individuals in gangs could increase the risk of associating with misinformed 81 peers, especially if some individuals are more social than others (Pruitt et al., 2016). Across the animal 82 kingdom, genetically-related groups such as crèches promote associations between parents and 83 offspring (Balda and Balda, 1978; Clayton and Emery, 2007) that allow for learning (e.g. European shags 84 Phalacrocorax aristotelis: Velando, 2001; ravens Corvus corax: Schwab et al., 2008; vervet monkeys 85 Chlorocebus pygerythrus: van de Waal, Bshary and Whiten, 2014) and can even facilitate teaching (e.g. 86 meerkats Suricata suricatta (Thornton, 2006; Thornton and Raihani, 2010)). Alternately, some studies 87 suggest associations with non-kin can still be beneficial as these individuals may have a different range 88 of experiences (Hatch and Lefebvre, 1997). Describing group structures and understanding how these 89 affect associations should therefore help us to understand...

Changes in social groups across reintroductions and effects on post‐release survival

“…Using this method, we monitored known aggregations of juveniles that form every year (three consistent distinct aggregations in 2017, Fig. 1a, see Franks et al, 2018 for more information about group formation), but also captured associations for the few juveniles that did not frequent groups (17/108 juveniles). During each 1-h survey we recorded the identities of juveniles seen within a 15-m radius of the observer (VF): all hihi have an individual combination of coloured leg rings to allow identification by sight.…”

“…Most recent hihi translocations have moved juvenile birds caught at random from the population (Thorogood et al, 2013). Juvenile hihi are a social cohort and aggregate throughout late summer and early autumn at the end of each breeding season (Franks et al, 2018), but previous translocations have not taken this sociality into account. Prior to this study it was unknown, therefore, whether translocation altered social groups or what the consequences may be for population establishment.…”

Time Spent With Parents Varies With Early-Life Condition, but Does Not Predict Survival or Sociality of Juvenile Hihi

“…Following dispersal from their natal territory, juvenile hihi formed groups at three consistent sites (Franks et al, 2018c), each located at the bottom of separate gullies containing mature flora and a permanent water source (distances between group sites ranged from 200 to 1,000 m). To measure sociality of juveniles, we placed temporary supplementary feeders with PIT tag dataloggers (IB Technology) at each of the three sites for 6 weeks and collected 11,928 records of time-stamped visits from 64 individuals, including the 19 juveniles used to answer question (2).…”

“…No new individuals were recorded after 6 weeks, suggesting that the majority of hihi that used group sites were included in our dataset. See Franks et al (2018c) for more details on group behaviour and feeder use.…”

“…Variation in chick provisioning may be associated with long-term consequences for offspring fitness, for example the extent of expression of secondary sexual traits (Walker et al, 2013), indicating an importance of early-life condition. We also know that juveniles aggregate together in groups after dispersing from their natal territory (Franks et al, 2018c) and that they have lower survival if they suddenly lose these associates (Franks et al, 2018a), indicating social relationships may be important. However, we still know little about the postfledging period, or how this shapes survival later in life.…”