Shearwaters and prions_Hauraki Gulf_Photo Edin Whitehead.jpg

How adaptable are our seabirds

There is a need to better understand the foraging distribution and behaviours and diet of several species during breeding and assess how any variability in foraging distribution and effort affects breeding success. Foraging plasticity by seabirds may buffer any potential impacts from changing prey distributions, not only through fisheries impacts but also climate change. As seabirds are long-lived and many are slow to mature, they may struggle to adapt to rapidly changing environmental conditions compared to species with shorter generation times. Also, burrow nesters (e.g., petrels, shearwaters, prions, little penguins) are extremely faithful to their colonies (natal site fidelity), which with prey-shifting could make the distances travelled to find food longer and unstainable. Whereas surface nesters (e.g., gannets, gulls, terns) are better able to up-stakes and set up nesting closer to their feeding grounds. The following examples look at how seabirds are coping with these changes.

   

  • Tākapu / Australasian gannets from colonies in the Hauraki Gulf exhibit spatial separation in terms of foraging distributions. Recent aerial surveys show there has been a marked increase of the population of the outer Gulf colony (Mahuki) with what appears to be a corresponding loss to inner Gulf populations (Horuhoru Rock and Motukawao Islands). Potentially, this reflects a changing distribution of certain food species between the inner and outer Gulf.

  • Rako / Buller’s shearwaters breed only on the Poor Knights Islands. While commonly seen within Hauraki Gulf, Northland, and Bay of Plenty waters, they also make long provisioning trips well beyond these areas. Their foraging distribution, together with results of recent stable isotope studies showing feeding across three different trophic levels with krill, fish and squid identified in regurgitations suggests a degree of plasticity during breeding. However, recent marine heat-wave events may increase the pressure on these birds.

  • Pakahā / fluttering shearwaters commonly forage around significant bathymetric and hydrodynamic features such as reefs, and around and between islands, within continental shelf waters in association with shoaling fish. Regurgitations from fluttering shearwaters show close correlation to the prey the fish are also feeding on (i.e., krill). However, besides krill, fluttering shearwaters also feed on small bait fish, often feeding in association with fast-moving kahawai and skipjack tuna schools later in the season.

  • Tītī wainui / fairy prions by contrast are something of a zooplankton specialist, although they do take larval fish. In northern New Zealand they breed only on the Poor Knights Islands in very large numbers. Their breeding success is largely dependent on their association with tightly packed schools of trevally, kahawai, and mackerel that we find around islands and prominent bathymetric features. Any decline in occurrence and scale of these fish schools could impact heavily on this northern population. 

  • Kuaka / northern common diving petrels are another zooplankton and small fish specialist. However, unlike fairy prions, they do not associate with fish shoals. They are a central place forager with contrasting foraging behaviours to fairy prion, and, to lesser extent, fluttering shearwater. Recent tracking has shown differences in foraging between birds breeding in the outer Gulf (Burgess Island, Mokohinau Group) and Tiritiri Matangi in the Inner Gulf.  

  • Tara / white-fronted terns are a visual forager and catch their prey (small fish, krill, and squid) close to the surface by aerial dipping. They can also move their nesting locations from season to season, unlike the burrow-nesting seabirds. Changes in prey availability and distribution may account for this ephemeral nesting behaviour, a case of the birds following the food.

  • Kororā / little penguins do not have the ability to fly and therefore are more restricted in their movements, most foraging trips are <24hrs when feeding chicks. As a visual forager their feeding can potentially be severely affected by increased turbidity during storm events. Also, with their foraging out from scattered small colonies along inhabited coastlines of the mainland and large islands (i.e., Aotea, and Waiheke and Kawau Islands) makes them susceptible to increase in toxic algal blooms in coastal waters from terrestrial runoff.