Using long-term data, IPMs, & expert judgement, Fischer et al. demonstrate how translocation feasibility can be assessed quantitatively and transparently for endangered, philopatric, and highly mobile species, such as Kuaka.

Kuaka, or Whenua Hou Diving Petrels, are in dire straits. The population of this Critically Endangered seabird is estimated at ~200 adults. Kuaka occupy the smallest breeding area of any bird species in Aotearoa New Zealand, and potentially the world; they only breed in 2.6 ha of coastal sand dunes on Whenua Hou, a remote, uninhabited island.

Whenua Hou was cleared of invasive predators in 2000, but despite those efforts, the Kuaka population is not increasing as expected. Ongoing threats to Kuaka include storms and storm surges that erode the breeding colony, Common Diving Petrels that compete with Kuaka for burrows, and artificial light at night on vessels that cause deck strikes. Climate change will likely exacerbate these challenges. Consequently, a conservation translocation appears to be the best strategy to recovery the species if there is suitable destination site.

Challenges to Kuaka translocations

Conservation translocations of Kuaka are extremely challenging. There are only ~200 adults that produce ~50 fledglings each year. Harvesting fledglings to establish new populations might cause population declines on Whenua Hou. Yet, sufficient fledglings would need to be harvested to establish a new population. Captive breeding or cross-fostering to provide extra fledglings is not an option.

Kuaka are philopatric and fly thousands of kilometres every year. Kuaka usually return to the same breeding colony, so even after successfully fledging, translocated Kuaka could return to Whenua Hou as adults. Even if some adults did establish at a destination site, their offspring might return to Whenua Hou, as metapopulation dynamics of highly mobile species, such as Kuaka, are poorly understood. Uncertainty around these metapopulation dynamics and vital rates at a potential destination site abounds. In these tricky situations, the current IUCN translocation guidelines offer little help, as they highlight issues to consider but not a methodology for making quantitative predictions.

A way forward

We aimed to quantitatively assess the feasibility of Kuaka translocations in the light of challenges such as balancing harvest impact on the source with establishment success at the destination, philopatry, metapopulation dynamics, and the ubiquitous uncertainty.

First, we compiled the available long-term data: mark-recapture data going back to 2002 and burrow monitoring data from obtained through burrowscopes going back to 2017. Combined, these data provided the foundation for our model.

We employed the statistical power of modern integrated population models, allowing us to estimate vital rates and population size, while accounting for environmental and individual stochasticity, and covariance among vital rates.

Additional parameters still had to be estimated. How likely were harvested fledglings to survive translocations? How likely were Kuaka, fledged at the potential destination site, to return to Whenua Hou as adults? How will vital rates at the potential destination site differ? To answer those questions for which we had no data, we built a user-friendly Shiny app. Through this app, we hosted an expert elicitation and integrated explicit judgement in our population model. We then simulated translocation scenarios and, ultimately, assessed the feasibility of Kuaka translocations.

Kuaka translocations are feasible

Our simulations show that Kuaka translocations are feasible. Small short-term declines in the source population should be expected due to harvest impacts, but these harvests can successfully establish a second colony, despite philopatry causing some translocated fledglings to return to the source as adults. Further metapopulation dynamics between source and destination are likely to modulate the effects of harvests and establishment success.

Conservation translocations are risky. Yet, the extinction probability for Kuaka is low in the short-term, even under risky translocation scenarios. A conservation translocation for Kuaka thus appears a feasible management alternative. As such, conversations with landowners are now ongoing to confirm the potential destination site.

Our methodology enables transparent, quantitative prediction of translocation feasibility for all challenging translocation scenarios. As such, our approach is a considerable improvement on current qualitative assessments.

Read the full paper Predicting harvest impact and establishment success when translocating highly mobile and endangered species in Journal of Applied Ecology