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

Reintroductions are essential to many conservation programmes, and thus much research has focussed on understanding what determines the success of these translocation interventions. However, while reintroductions disrupt both the abiotic and social environments, there has been less focus on the consequences of social disruption. Therefore, here we investigate if moving familiar social groups may help animals (particularly naïve juveniles) adjust to their new environment and increase the chances of population establishment. We used social network analysis to study changes in group composition and individual sociality across a reintroduction of 40 juvenile hihi (Notiomystis cincta), a threatened New Zealand passerine. We collected observations of groups before a translocation to explore whether social behaviour before the reintroduction predicted associations after, and whether reintroduction influenced individual sociality (degree). We also assessed whether grouping familiar birds during temporary captivity in aviaries maintained group structure and individual sociality, compared to our normal translocation method (aviaries of random familiarity). Following release, we measured if survival depended on how individual sociality had changed. By comparing these analyses with birds that remained at the source site, we found that translocation lead to re-assortment of groups: non-translocated birds maintained their groups, but translocated juveniles formed groups with both familiar and unfamiliar birds. Aviary holding did not improve group cohesion; instead, juveniles were less likely to associate with aviary-mates. Finally, we found that translocated juveniles that lost the most associates experienced a small but significant tendency for higher mortality. This suggests sociality loss may have represented a disruption that affected their ability to adapt to a new site.

help animals (particularly naïve juveniles) adjust to their new environment and increase the chances of 23 population establishment. We used social network analysis to study changes in group composition and 24 individual sociality across a reintroduction of 40 juvenile hihi (Notiomystis cincta), a threatened New 25 Zealand passerine. We collected observations of groups before a translocation to explore whether social 26 behaviour before the reintroduction predicted associations after, and whether reintroduction influenced 27 individual sociality (degree). We also assessed whether grouping familiar birds during temporary 28 captivity in aviaries maintained group structure and individual sociality, compared to our normal 29 translocation method (aviaries of random familiarity). Following release, we measured if survival 30 depended on how individual sociality had changed. By comparing these analyses with birds that 31 remained at the source site, we found that translocation lead to re-assortment of groups: non-32 translocated birds maintained their groups, but translocated juveniles formed groups with both familiar 33 and unfamiliar birds. Aviary holding did not improve group cohesion; instead, juveniles were less likely Introduction 38 39 Reintroduction, returning species to parts of their range where they have become extinct (IUCN/SSC, 40 2013), is important for many conservation programmes (Armstrong and Seddon, 2008). The process of 41 moving animals to a new site ("translocation" (IUCN/SSC, 2013)) and overcoming post-release effects To understand how group structure and familiarity impacts on translocation success, we therefore first 68 need to determine if groups remain together when they are moved to a new site. One challenge in wild 69 animal groups is there may be limited knowledge of familiarity before translocation. For example, studies 70 in New Zealand bird species (tīeke/saddleback, Philesturnus carunculatus rufusater; toutouwai/North 71 Island robin, Petroica longipes) and howler monkeys (Alouatta seniculus) found that pre-capture 72 familiarity was not maintained over translocation (Armstrong, 1995;Armstrong and Craig, 1995; 73 Richard-Hansen, Vié and De Thoisy, 2000). However, these species are territorial, and the studies also 74 defined familiarity from short-term binary measures (individuals in the same place upon capture were 75 "familiar", versus "non-familiar"). When longer-term measures of familiarity have been used for more 76 social groups (such as families or colonies) there is evidence that group composition remains similar 77 before and after reintroduction (Clarke, Boulton and Clarke, 2003;Shier, 2006; Pinter-Wollman, Isbell 78 and Hart, 2009) and that maintaining groups results in higher post-release survival (Shier, 2006).

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Therefore, capturing group familiarity over a longer time period for social species may be required to 80 assess the importance of maintaining or disrupting relationships over translocations.

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Here, we use a translocation of hihi (stitchbird, Notiomystis cincta) to test fitness effects of network 132 structure, and assess whether maintaining sociality can improve the outcome of a translocation. This 133 species is a threatened New Zealand passerine (Birdlife International, 2017) which was once 134 widespread across the North Island. Following the introduction of non-native predators when humans 135 arrived in New Zealand, hihi became restricted to a single off-shore island (Hauturu-o-Toi/Little Barrier 136 Island). Since the 1980s a major aim for conservation of this species has been to establish re-introduced 137 populations in predator-controlled areas, and the most recent hihi translocations have involved moving 138 juvenile birds. This cohort appears to be particularly social: juveniles form groups for several months at 139 the end of the breeding season and interact, for example with "play"-like behaviour and allopreening.

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However, it is unknown whether translocation alters these social groups or what the consequences may 141 be for establishment of populations. We used the opportunity of a translocation in 2017 to test our 142 predictions that: (1) translocated hihi will group with more familiar individuals from either before the 143 translocation, or based on who they were held with during temporary captivity; (2) individuals will remain 144 consistent in their sociality before and after translocation; and (3) any changes in social behaviour will 145 affect survival after translocation. In 2017 we reintroduced hihi to Rotokare Scenic Reserve ("release site", 39°27'15.4"S 174°24'33.0"E) 152 from Tiritiri Matangi Island ("source site", 36°36'00.7"S 174°53'21.7"E). The source site is a 220ha island 153 scientific reserve of replanted and remnant native fauna which is free of non-native mammalian 154 predators. Hihi were reintroduced to the island in 1995 (Armstrong and Ewen, 2001), and the population (numbering c. 270 in 2017) is now the main source of birds for ongoing translocations to other sites. The 156 release site (230ha, including a 17.8ha lake) is a mainland site of old-growth native forest surrounded 157 by a fence that excludes non-native mammalian predators. Hihi had been locally extinct at this site and 158 in the surrounding region for c.130 years prior to the reintroduction (Angher, 1984).

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This ensured we observed associations among juveniles commonly seen at group sites and also 167 associations with the few juveniles that did not frequent these sites (17/108 juveniles were never seen 168 at group sites). During each one-hour survey we recorded the identities of all juveniles seen within a 10-169 metre radius of the observer (VF). All hihi have an individual combination of coloured leg rings (applied 170 to nestlings during routine nest monitoring) so each could be identified by sight. We assigned juveniles 171 to the geographical location where they were observed: 40 birds were only ever recorded in the 172 northernmost groups ("north"), 16 at the southern end of the island ("south") and the remaining 49 mixed 173 between the two (mixed).

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Next, we constructed a "group-by-individual" (GBI) matrix where a group comprised any juveniles seen 176 within 15 minutes of the preceding bird. If we did not see any birds during this time, we considered the 177 next juveniles encountered to be part of a new group. This "gambit of the group" approach (Whitehead,   provided a more detailed measure of familiarity rather than binary familiar/unfamiliar: each "edge" 183 connecting two juveniles represented at least one co-occurrence in a group, so repeated co-occurrences 184 (and stronger edge weights) would indicate that juveniles were more familiar. We detected "communities" of frequently co-occurring individuals in the network using the community detection 186 algorithm of Clauset et al. (2004) implemented with the "fastgreedy.community" function (igraph R 187 package version 1.0.9, (Csárdi and Nepusz, 2006)). We ensured that assigned communities were robust   visual contact between aviaries (aviaries were therefore not in auditory isolation from each other or free-206 living birds). Each juvenile was assigned to an aviary based on its community in the network before 207 translocation: one aviary contained birds from one community only ("familiar" group), while the remaining 208 two aviaries contained birds from all communities ("mixed" groups, the normal management used in 209 previous hihi translocations). We ensured that mixing juveniles from different communities also included 210 spatially-separated birds (i.e. only detected in northern or southern survey locations) that had little 211 chance to interact prior to capture.

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All birds for translocation were caught within 24 hours, then kept in the aviaries for four further days 214 while samples were processed for disease screening. Each aviary held equal numbers of birds. During holding we provided supplementary food twice daily, using the same range of food used in previous 216 successful hihi translocations (Ewen et al., 2018). On the evening of the 1 st April, hihi were re-caught 217 from the aviaries, given standard health checks, and transferred to translocation boxes (five hihi per 218 box). We transported all birds at the same time from the source site to the release site, overnight (by 219 boat then van) to minimise stress for the birds. All hihi were released successfully the following morning 220 (2 nd April).

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For each translocated hihi, we created encounter histories which represented each bird's presence ("1", seen) or absence ("0", not seen) in each successive survey or "time point". All individuals were assigned

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To assess whether maintaining familiar groups during capture for translocations affected individual 296 sociality, we calculated each translocated juvenile's change in degree rank after translocation compared 297 to before translocation (bound between -1 and 1; a negative value represented a decrease in social 298 rank; a positive value was a rank gain). We used a Linear Model (LM) with rank change as the response.

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Our predictors included the aviary type each bird was housed in ("familiar" or "mixed" aviary) in 300 interaction with degree before translocation (effects of aviary could depend on sociality), and sex. For 301 this analysis, we included number of observations both before and after translocation as fixed effects, 302 because change in rank score (our response) could be dependent on variation in both number of 303 observations. Again, we assessed significance of both analyses using data-stream permutations.

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We did not include covariates in this starting model as there is currently no method for GOF testing with    Figure 2). Additionally, translocated juveniles did not associate more 352 strongly if they had shared an aviary, even when they had been familiar at the source site; in fact, there 353 was a tendency for a weak disassociation by aviary (Table 2c; r = -0.09, Prand = 0.04, Figure 2

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Individual sociality was not consistent: more social juvenile hihi before translocation were not more social 408 after the translocation at either the source site or release site (Table 3a, Figure 3a). Post-translocation 409 social ranks did not differ between males and females (Table 3a) and also did not vary depending on 410 how many times a bird was re-sighted any more than expected by random chance (Table 3a). Among 411 translocated hihi, some birds experienced greater degree rank changes than others (greatest rank gain 412 = +0.59; greatest rank loss = -0.68) but this was not predicted by their degree rank before translocation 413 (both more-and less-sociable individuals were equally likely to change rank; Table 3b, Figure 3b).

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Individual degree rank was not preserved by holding a juvenile with its familiar group-mates in an aviary 415 during the translocation (no significant difference in degree rank change between birds housed in 416 familiar and mixed aviaries; Table 3b, Figure 3b). Finally, the extent of rank change was not significantly 417 different between males and females (Table 3b), and again was not significantly affected by re-sighting 418 before or after translocation compared to permuted networks (Table 3b).   419   420  421  422  423  424  425  426  427  428  429  430  431  432  433  434  435  436  437  438  439  440  441  442  443  444  445  446   Table 3. Results of (a) GLM analysing variation in post-translocation degree ranks and (b)

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Associates may be particularly important when individuals need to rely on social information more: for 546 example, when they have little personal information, such as following reintroduction to a new site

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Importantly, pre-and post-event sociality was not consistent for each foal, and post-event sociality was 551 especially important for survival, which suggests the current social environment conferred the strongest 552 advantages (Nuñez, Adelman and Rubenstein, 2015). In hihi, we found similar patterns as relative pre-553 and post-translocation sociality did not remain consistent for both translocated individuals, and birds that 554 remained in the source environment (but did experience social disruption through the removal of peers).

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In our study, however, changes in sociality only had costs for survival when additionally associated with