Search Results For Fiordland Bat Diaries

We join the Te Anau bat monitoring team at the end of their Eglinton short-tailed bat season. They are pretty excited as they have just recorded a new population highest count of 4179, superseding the last record set in 2018 by over 1000 bats!

The saying goes ‘you can’t see the forest for the trees’ but often these days people don’t seem to see the trees for the forest. To the untrained eye a beech forest can look all the same, one tree the same as another, next to another just the same. Trees seem endless, expendable. But trees are not all the same, even when they look the same from the outside. In the forest old trees are the safe havens for many.

📷: Warren Simpson

Meet M72. M72 is a red beech tree, Fuscospora fusca, found in the Eglinton Valley, Fiordland National Park. According to our records M72 was ‘discovered’ in 2009, is about 30m tall with a diameter at breast height of 140cm. This makes M72 about 700 years old give or take. That’s far older than the measly 200 years Europeans have been around in Aotearoa and only slightly younger than the time Maori have inhabited this land. From the outside M72 looks like any other grand old tree in the forest, however M72 holds a secret.

📷: Warren Simpson

And what is that secret? A home big enough for over 4000 southern short-tailed bats! That’s about 60kg of ‘bat weight’ hanging from the inside the tree, rather a lot of bat to fertilise the tree from the inside…Homes for NZ bats are mainly tree cavities, the occasional cave if there happens to be one around, and sometimes just a piece of bark or vegetation for a single bat to hide under. Bats move home regularly so need to have an array of trees to choose from, spending as little as one night in some trees. Young trees don’t provide good roosting opportunities, the older the better to develop cavities and palaces inside.   

📷: DOC

We only get to monitor this bat colony for one month each year so there is a lot we don’t get see or understand about their movements, but years of monitoring them generally gives us counts of 1 to 1600 bats in a tree. Which means there M72 is very unique, even amongst other large old trees, that allows it to be home to so many bats. Maybe M72 is the only tree in this forest with a large enough cavity to fit everyone in? That’s something to think about.

📷: Warren Simpson DOC

M72 it’s a great privilege to know you, hope you live for many years to come.

Catching bats is a tricky business. We have a few tools up our sleeve to help like special nets and traps but when you are looking for a needle in a hay stack a lure helps too. Effective and inexpensive acoustic lures are a work in progress so for years we have used a cheap easy option which works for short-tailed bats, a bird squeaker. It makes both sounds audible to us (similar to audible sounds bats make) and ultra-high-pitched sounds we can’t hear but the bats can. But what to do when you are a helicopter flight away from home and that small but precious piece of kit has been forgotten!?

Play the saw of course!

The Saw
📷: Bex Jackson DOC

Based in a small two person hut options for a replacement bird squeaker were lacking. A bird squeaker is a piece of metal with a wooden surround you rotate, the friction between the two makes the squeaking sound, with the help of rosin used on violinist’s bows. After some trial and error going through possible hut options, a small piece of wood rubbed against the wood saw were found to be the best substitute. And it sure did the trick, 16 bats were lured into our net before midnight by the sweet (but rather unpleasant) sound of the saw playing.

📷: Jamie McAulay DOC

It is hard to know what exactly the bats are attracted to, whether it is the audible or ultra-high pitched sounds. Another one of the million unanswered questions relating to bats. But it works and that is enough for us. Indeed a visiting German bat researcher was so taken with the technique that we gave her one of our spare bird squeakers and she has now revolutionised catching bats in Germany.

📷: Warren Simpson DOC

I’m thankful for the saw but it isn’t the most user-friendly lure to use, its transportableness for one thing is a bit wanting. Next time I’ll be triple checking the bird squeaker is packed before heading away.

📷: Jamie McAulay DOC

If you missed Fiordland Bat Diaries Part 5 – Trees check it out here to learn about some of our fantastic forest

Local rangers in Fiordland undertake short-tailed bat monitoring in order to protect and learn more about these special, little native critters. But sometimes they are not the only little critter on show…. The New Zealand bat-fly is a wingless fly that lives alongside short-tailed bats and is a creature of nightmares for some.

Bat with a few hitch hikers.
📷: DOC, Louise McLaughlin

Bats are not the only endangered species we run into doing bat work. The New Zealand bat-fly Mystacinobia zelandica is a species of wingless fly that has evolved to live alongside short tailed bats. At some point they decided hitching a ride on the back of a bat was easier than flying and so lost their wings. Unfortunately, this gives them a somewhat spider like appearance which isn’t all that endearing, the first of their un-endearing traits.

Bat-fly having a meal on the go.
📷: DOC, Warren Simpson

Bat-flies are the housekeepers/ waste disposal workers in bat land. They have a symbiotic relationship where they feed on bat guano (bat dung) and keep things clean while the bats provide a warm safe environment with ample food. Females lay their eggs in large communal nurseries in the bottom of the guano pile and tend to the growing larvae.

Bat roosting tree from below.
📷: DOC, Jamie McAulay

However, life isn’t all peachy for bat-flies as there is a constant threat of being left behind at a roost tree when the colony moves on. Every evening when the bats depart, they must make a gamble on whether to stay or leave. Leaving means hitch hiking on a bat for the evening while the bat-flies all night, and staying means feeding at the roost tree. But once the colony moves away from a tree for the final time, any remaining bat-flies will slowly die as their food supply dwindles. This makes those stranded individuals pretty desperate to find a new home and when we climb the tree to take down our monitoring equipment, they swarm out seeking our heat, coming down the climbing rope to greet us.

Masses of bat-flies at a bat roost entrance.
📷: DOC, Colin O’Donnell

For us bat-flies are a part of life while we handle bats. They crawl off their hosts and onto us – on average there are about 5 per bat hanging on (though up to 30 on one individual have been seen). And while we endeavour to re-home as many as we can back onto the bats before release, come the end of the evening there are inevitably flies crawling around on our legs, in our hair, the back of a neck. We find them days later in our beds, packs, and even in a toothbrush…

A stranded juvenile with hitch hikers.
📷: DOC, Bex Jackson

Catch the team next time on the Conservation blog to take a closer look at the mighty trees that these bats roost in.