Linking sea and shore with shag science

Department of Conservation —  20/05/2020

Written by Technical Advisor, Casey Spearin

The sight of a shag drying its wings in the sun will be familiar to most. Less well-known is that the presence of shags can indicate that the surrounding marine and land environments are healthy and functioning.

A little black shag resting on a rock at Waikanae estuary.
📷: DOC

Effective conservation relies on knowing the state of the environment and how it is changing, but it’s not possible to record every variable in an environment. A good indicator – something which is reliable and practical to measure – can give a surprising amount of insight about the wider state of the environment.

Shags are large, easy to identify, and live together in colonies, which makes them relatively straightforward to study. Simply counting these birds and recording their numbers over time is a useful way of tracking the health of the marine environments where they live. For our marine reserves, this means better management decisions, and earlier warning signs of issues.

Pied shags. Shags like to establish roosts in macrocarpa trees, like this one.
📷: DOC

Our on-going partnership with Air New Zealand has enabled DOC’s Marine Ecosystems team to set up a research project studying shags around Kapiti Marine Reserve. The partnership has also included hands-on support during shag counting trips from the airline’s Greenteam, an internal group of conservationists. This research aims to set a baseline for shag activity in Kapiti so that DOC and community groups can monitor changes in the environment over time.

“Kāpiti is a really interesting place to do this work”, says Emma Hill, Technical Advisor. “Shags are an important link between land-based and marine ecosystems, since they feed on fish but add nutrients to coastal land via their guano (droppings).”

And around the marine reserve are three very different land environments: Kāpiti Island, an established nature reserve; Mana Island, regenerating forest after three decades of farming; and the mainland, an increasingly urban environment.  

Technical Advisor Emma Hill keeping a keen eye on Mana Island.
📷: DOC

“Having these diverse environments in close proximity makes it a great place to do this research because the places where the shags are roosting are different, but the places where they feed may overlap.”

Many coastal bird populations, including shags, are affected by increasing human activity and coastal development. Climate change also affects seabirds by changing the size and distribution of the fish populations that they feed on. In comparison to land bird conservation, there has been limited focus on seabird conservation in New Zealand, especially considering it is the world centre of seabird diversity.  

Emma says although shags are common, we don’t know a lot about them. “They are deserving of more attention. Research has been carried out on boat trips to scope the project. We want to know how many of each species there are, how this is changing, and what effect the marine reserve and scientific reserve are having.”

Shortly before lockdown, she was on Mana Island studying the colonies, counting how many shags are returning to their roosting sites at dusk over three consecutive nights. Of particular interest is the effect that the ongoing regeneration of Mana Island may have on seabirds. This study will be repeated in a few months—and eventually extended to other known shag colonies including those at Waikanae Estuary. DOC fieldwork is resuming as COVID-19 restrictions lift, and the team is eager to get back onto the water and continue learning about these special birds.

The shag survey team takes a rest while combing the shoreline for suitable habitats.
📷: DOC

“We’ve seen birds feeding around Kāpiti island and we spotted some pairs in rocky crevices on the east and south of the island, but we haven’t seen any colonies on our boat surveys yet. They could be roosting further inland than we could see.”

“There’s also a lot we could learn if we GPS-tracked some shags around Kāpiti. As far as we know, this hasn’t been done before. The technique has potential to show where they’re going to feed and rest, and paint a good picture of what’s going on in the marine environment.”

Pied shag in flight.
📷: DOC

Connecting with iwi and the community is essential for the project, and Emma has been busy researching and talking to iwi, locals, the Ornithological Society, and community conservation groups such as the Waikanae Estuary Care Group, Kāpiti Biodiversity Project, and Guardians of Kāpiti Marine Reserve.

Years of work by these community groups have proven essential to establishing this programme, and community members are highly encouraged to continue contributing to monitoring seabirds in their area.

“We’re trying to build up our knowledge, we recognise that there are many people who can help us fill the gaps. Your involvement with the project is welcomed.”

  • If you have information to contribute, please get in touch by emailing
  • If you see a shag near Kāpiti, take a photo and upload it to the project on iNaturalist.
Video of the team out counting shags on Mana Island.
📹: DOC