But who's counting (we are!)

By Conservation Lead Ranger, Ellen Irwin

Imagine being in a forest filled with manu/birds and trying to count them all. A kākā swoops past in the blink of an eye. Is that tīeke/saddleback, foraging noisily, one that you’ve already counted? Pōpokotea/whiteheads chatter and flutter everywhere, causing you to recount every time they shift around you. How could anyone hope to estimate these numbers?

Thankfully, this issue can be solved using a method called the five-minute bird count (5MBC). This method originates from when the New Zealand Government announced the ‘South Island Beech Utilisation Project’ in 1971, which proposed large-scale harvesting of forests on the South Island, and the creation of unlogged reserves. To determine the best sites for these reserves, the Department of Scientific and Industrial Research (DSIR) and the Wildlife Service needed a method to count native forest birds to determine which forests had the greatest bird diversity or were preferred by certain key species. At the time, there was no internationally recognised, standardised method for doing a bird community census. DSIR researchers tested a variety of techniques and ended up recommending the 5MBC method.

What is a five-minute bird count?

The 5MBC method involves an observer standing at particular ‘count stations’ and recording the number of birds they see or hear around each station within five minutes. It really is that simple and requires only binoculars and a notebook!

Counts are generally repeated at a variety of stations, located at least 200m apart. Observer skills and hearing abilities, ease of detecting manu/birds in a particular habitat, weather, and season can all influence the count. For example, counts during or just after breeding season can be tricky, as some manu may be less likely to call when they are busy incubating eggs or feeding chicks. In addition, fledgling calls can sound very different to adult calls, and it can be difficult to distinguish the high-pitched fledgling calls of different species!

One of the important things to remember about 5MBCs is that it is an index measure. This means it does not measure the actual number of birds. Even so, it can be great for detecting differences, both between two populations in a particular year or within a population over time. In addition, not all manu are easily detected using this method (e.g., manu that don’t call very often like kākāriki). There are other methods that are more intensive that can be used which are more appropriate for these species.

The legacy of five-minute bird counts

Since the 1970s, there have been hundreds of studies that have used this method, leading to a huge count collection (over 200,000!). These counts are an incredibly valuable resource as they provide a historical baseline of manu numbers and therefore allow for the investigation of long-term trends. 5MBCs have been used to argue for the protection of particular areas, monitor progress in restoration projects, and investigate changes in manu populations over time.

At Zealandia, we have 40 count stations situated throughout the valley. Members of Birds NZ set these up back in the 1990s and were able to collect data on the bird community in the valley both prior to the fence going up as well as afterwards. Dr Colin Miskelly analysed this long-term dataset and found that while many species (e.g., tūī and translocated species like tīeke and kākā) increased markedly in detection in the years following mammal eradication and/or their reintroduction, others (tauhou/silvereye, riroriro/grey warbler, pīwakawaka/fantail) decreased in detection. Miskelly suggested that these species could have been outcompeted by the native species that have greatly benefitted from mammal removal. Excitingly, he found that Zealandia’s bird community is now more like Kapiti Island’s than the community present prior to the sanctuary’s creation!

Today, Zealandia staff undertake 5MBCs in the valley at those same stations twice a year, in October and April (roughly pre- and post-breeding season). We follow the Birds NZ method of having each station repeated by four different observers, twice in the morning and twice in the afternoon. Because of the amazing dataset collected by Birds NZ members, we can keep an eye on a wide range of species and their population trajectories over time. This means we're able to keep tabs on many species without having to intensively monitor them. If the counts for a particular species declined or dropped suddenly, we could then trigger increased monitoring or management actions to prevent a population crash.

Next time you are in the ngahere/forest, stop and listen to the calls around you and practice doing your own 5MBC. Our Whānau Activity Book has the perfect space to record what you hear and see!

Photo by Ian Thomas