Bush stone-curlews that joined resident birds after release stayed closer to the release area and used larger core ranges than birds that remained in an exclusive group of later arrivals, a GPS-tracking study found. The contrast was strongest between the mixed group, where reinforcers joined residents, and the exclusive reinforcer group. Short-term survival did not differ significantly between the 16-bird resident cohort and the 19-bird reinforcer cohort.
The result suggests that social organisation may be tied to how translocated birds settle into new space. It does not show that joining residents caused the tighter movement pattern or improved survival. Because birds self-selected into social groups, individual traits associated with integration could also account for the differences.
A split emerged after the second release
Researchers tracked 35 adult captive-bred bush stone-curlews released in sequence. Sixteen formed the resident cohort, while 19 were released later as reinforcers, the study's term for the later cohort. Social links were inferred from GPS proximity, not direct observation. The network analysis used a 330-second time criterion and a 30-metre distance criterion, then applied a weighted community method to identify groups.
The social picture was not one unified flock. Before reinforcement, the resident network had 87.2% edge density, meaning most possible proximity links were present. Afterward, the full network reached 100% edge density, but the analysis still identified two groups and one lone bird. Ten reinforcers joined eight residents in a mixed group, while nine reinforcers stayed in an exclusive group.
Movement separated the groups
Daily distance travelled by reinforcers increased at first, then the increase slowed and eventually declined. Exclusive reinforcers had a lower increase rate than both residents and mixed reinforcers. The mixed group did not differ significantly from residents on that trend, so the clearest contrast was between reinforcers that integrated with residents and those that remained exclusive.
Distance between consecutive roosts followed a similar rise-and-fall pattern. Exclusive reinforcers moved farther between roosts than residents, while mixed reinforcers did not differ significantly from residents. Distance from the release site separated all three groups over time: exclusive reinforcers dispersed 3.6 times faster than mixed reinforcers. Mixed reinforcers and residents settled in central woodland, while exclusive reinforcers moved toward the eastern boundary.
The birds' core ranges, the central parts of their tracked ranges, showed the same ordering: residents had the largest, mixed reinforcers were intermediate, and exclusive reinforcers had the smallest. Mixed reinforcers lost a mean 109.25 grams, or 13.8% of body mass, compared with 140 grams, or 17.3%, among exclusive reinforcers. The weight-loss difference was not statistically significant.
Residents changed too
The initial cohort also changed its movement around reinforcement. Daily distance travelled and core-range size dipped immediately after the later birds were released, while roost displacement rose. Later trajectories reversed or exceeded the pre-reinforcement patterns, and residents moved up to 3 kilometres beyond the fence. Distance from the release site itself showed no immediate shift.
The authors interpret the later pattern as greater roost-site fidelity alongside expanded movement. But this was a pre/post observational comparison without an independent untreated control, so the timing alone cannot establish that reinforcement caused the change.
A bigger head count, but unanswered questions
At population level, the observed count rose from eight individuals before reinforcement to 27 afterward. Yet only 10 of the 19 reinforcers joined the resident community, and reproduction was not monitored. The increase therefore shows a larger observed population, not whether the population will reproduce or remain viable over the long term.
Survival was assessed over a common 55-day period: 87% of residents and 95% of reinforcers survived. The cohort difference was not statistically significant, and few mortality events limited the study's power to detect one. GPS-derived social links and the short follow-up add caution to interpreting the movement differences.
Taken together, the study supports a practical hypothesis for future translocations: resident social structure may matter alongside survival when managers decide how and when to reinforce a population. It does not establish a causal social effect, and its longer-term demographic consequences remain unknown.
Paper data and sources
Original title: Social Group Membership With Residents Mediates Reinforcement Outcomes for a Translocated Bird.
Authors: Shoshana Rapley, Maldwyn J Evans, Heather M McGinness et al.
Journal/Repository: Ecology and evolution
Status: Peer-reviewed
First online: 2026-08-20
DOI: 10.1002/ece3.74136
Original paper