Seabird recovery can be rapid after predator eradication on islands, but it also can not be rapid at all. We investigated spatial and ecological influences on seabird recovery to islands following the eradication of introduced predators our paper: A GIS-based decision-making approach for prioritising seabird management following predator eradication, published in Restoration Ecology..

We used a large dataset of seabird census estimates on 69 islands in the Hauraki Gulf, Aotearoa. The region is a seabird diversity hotspot, supporting breeding populations of 27 seabird species and has a long history of predator invasion and eradications.

These data, along with ecological data that is specifically related to habitat preferences of seabirds and behavioural parameters were used in GIS-MCDA (geographic information systems – multi criteria decision analysis) to evaluate the constraints on recovery following predator eradications.

We identified nine islands with low observed passive recovery of seabirds post-eradication over a 50‐year timeframe, and classified these as sites where active seabird management could be prioritized. Such spatially explicit tools are flexible, allowing for managers to choose case‐specific criteria such as time, funding, and goals constrained for their conservation needs. Furthermore, this flexibility can also be applied to threatened species management by customizing the decision criteria for individual species’ capacity to passively recolonize islands. On islands with complex restoration challenges, decision tools that help island restoration practitioners decide whether active seabird management should be paired with eradication can optimize restoration outcomes and ecosystem recovery.

You can get a PDF here.

My colleagues and I recently published an article in the Journal of the Royal Society of New Zealand about the intractables; species that continue to decline despite conservation action.

The lovely seabird Toanui/flesh-footed shearwater featured among the intractables. Toanui feeds mainly on squid and fish and the New Zealand colonies of the species represent 16 % of the global population. Since the 1930s, at least four New Zealand colonies have vanished. Rats may be to blame, however, even on rat-free islands the population is decreasing. It is likely that the birds suffer from high levels of mortality from fisheries bycatch, as well as plastic pollution, which has been found in the digestive tracts of birds and chicks. In New Zealand the birds have been a low priority for conservation funding, however, predictions are the local population will be halved by 2050.

Other examples of intractables include the Māui dolphin, Pīngao, kākahi, forest ringlet butterfly, hihi, and the grand and Otago Skinks. We argued that some of these species are headed for extinction if no additional actions are taken. We may be leaders in conservation in Aotearoa New Zealand, but that doesn’t mean we can rest on our laurels.

Our article featured in the New Zealand media at the Newsroom, and Stuff.

ABSTRACT

Global biodiversity loss is accelerating at an alarming rate. While considerable effort and resources have gone into conservation management for many threatened species in New Zealand (NZ), some species are still ‘losing the battle’ despite much effort, and others have been ignored altogether. Here, we present seven case studies to illustrate the breadth of complex, often ambiguous, threats faced by taxa in NZ. These threats originate from the effects of agriculture and harvesting, irreversible habitat modification and loss, impediments to connectivity, disruption of parasite–host relationships, introduced species and susceptibility to disease, and are further exacerbated by complexities of political and legal inertia, low prioritisation and limited conservation funding. We outline the conservation challenges and identify advances needed to meet NZ’s long-term conservation goals. The next 30 years of conservation require new tools in order to protect especially those ‘intractable’ species that have thus far defied efforts to ensure their survival.

Read the full article.

One of the most acute threats to seabirds is introduced predators, which depredate seabirds at all life stages from eggs to adults. Consequently, predator eradication has been identified as an effective and commonly used seabird conservation method. Seabird recovery post-eradication is influenced by complex and interacting environmental and demographic factors, though gaps remain in our understanding of the speed at which ecosystems respond to seabird recolonization. While monitoring seabird colonies post-eradication can help improve this understanding, limited resources and the remoteness and number of seabird islands challenge our ability to achieving long-term monitoring and research objectives. Therefore, economical and effective monitoring tools are needed.

Remote sensing has been used for decades in agriculture to evaluate crop nutrient status. Advances in remote sensing tools have improved the quality and reliability of applying this technology to evaluate a range of ecological systems. Seabirds can introduce large quantities of guano, effectively fertilising their island habitats. Concentrations of ammonia in soils have been positively correlated to seabird burrow density, and deposition rates of nitrogen into low nesting density systems can be as much as 3 times the rate of standard agricultural fertilisation rates.

Our research investigates if methods used for evaluating crop nutrient status on agricultural fields can be applied to a heterogeneous forest canopy. In this way, remote sensing could be used for monitoring long-term changes in seabird nesting density by evaluating canopy nutrient status. To test this hypothesis, we are investigating the relationship between seabird burrow density, and soil nitrogen and canopy level nitrogen on islands in the Mercury Island group, off the east coast of the Coromandel. We used a UAV (unmanned aerial vehicle) mounted multispectral sensor to collect extremely high resolution images (5cm).

This imagery is used to evaluate canopy composition and the spectral reflectance signature of pōhutukawa (Metrosideros excelsa), in relation to seabird density. We sampled and analysed soil and leaves from pōhutukawa trees on Korapuki (18 ha), Middle (13.5 ha), Green (2.5 ha), and Great Mercury (1867 ha) islands for total nitrogen and carbon:nitrogen ratios. Seabird nesting density on the islands ranges from low (1 burrow/m2) to high (10 burrows/m2).

As expected, we found a strong relationship between seabird nesting density and soil nitrogen. However, our preliminary results indicate this relationship is not strongly transmitted to the canopy of pōhutukawa (Journal of non-significant results?). This result may be attributed to the physiology of pōhutukawa, which is a highly stress tolerant species. Pōhutukawa distribution is predominantly coastal, trees must be adapted to salt spray, arid environments, poor quality soils, often establishing on rocky steep cliffs. We postulate that given these stress tolerant adaptions, pōhutukawa may uptake and store only the nutrients it requires for growth and homeostasis, and perhaps is limited by other resources, so is not responding to nutrient enrichment in a way that is detectable in canopy spectral reflectance.

With these results in mind, our research continues to evaluate the spectral response of other island canopy species to seabird nutrient enrichment, and the topographic and environmental influences that might affect forest canopy reflectance. In the coming field season, we will be evaluating the canopy species māhoe (Melicytus ramiflorus) and milk tree (Streblus banksii) to compare the results of pōhutukawa with and identify other species that may act as proxies for evaluating seabird nesting density changes over time.

Predator eradication is an effective tool for protecting New Zealand’s seabirds. However, to ensure that seabirds populations are stable or increasing in the face of additional threats, such as fisheries and pollution, long-term monitoring is needed. Developing methods using remote sensing technology provides the opportunity to achieve these goals in an affordable way, across larger spatial scales than has been previously possible.