What the night revealed: listening to pekapeka in the Rees and Glenorchy

Always feathers, no fluff — it’s time to start thinking about native mammals.

In spring 2025, in collaboration with Tāhuna Glenorchy Dark Skies and with the help of one of their amazing volunteers, 40 acoustic recording devices (ARDs) were deployed throughout the Rees Valley and Glenorchy to better understand the distribution and activity of pekapeka (long-tailed bat), a nationally threatened native species. 

New Zealand is home to two extant species of endemic bat; the long-tailed bat (Chalinoblus tuberculatus), and the lesser short-tailed bat (Mystacina tuberculata).

Both species echolocate, and communicate, via ultrasonic vocalisations. Accordingly, the human ear is generally incapable of eavesdropping on batty conversations — we convert their banter to a picture instead (Fig 1).

Figure 1. Spectrogram of a New Zealand long-tailed bat call sequence. Note the distinctive right-sweeping ‘tails’ at the 40 kHz base of each pulse — this pattern is typical of long-tailed bats. This spectrogram was produced by converting a Bitmap file (.bmp) to an image using Alato® Lab — a bioacoustics software.  

Our friends at DOC Queenstown have been monitoring long-tailed bats for more than a decade at the head of Lake Whakatipu, and we hear that these leather-winged fuzz-nuggets are responding well to predator-control operations. However, we don’t know very much about bat activity beyond Muddy Creek. Can we be doing more to help bats? Are bats roosting in the Rees? Could there be short-tailed bats lurking up valley? Perhaps. These questions ultimately catalysed the beginning of our own long-term bat activity index.  

Installing an ARD in Glenorchy

We recently processed 160,237 recordings from our first bat monitoring session and are elated to share our findings: 

Rees Valley

• Bat species detected: long-tailed bat. 

• Total number of long-tailed bat detections: 3,399 (of 95,584 recordings). 

• Number of recorders with long-tailed bat detections: 19 (of 19 recorders; min = 1 recording; max = 2,750 recordings).  

• Average number of long-tailed bat detections per detector-night (i.e., one detector operating for one night; to control for monitoring effort): 6.83 (± 27.47 SD). 

• Total number of bat-detector nights yielding long-tailed bat detections: 178 out of 498 detector-nights (i.e., 36% of detector-nights yielded bats). 

A special thanks to Rees Valley Station for their support of the project by allowing us to install ARDs across the station.

Glenorchy

• Bat species detected: long-tailed bat. 

• Total number of long-tailed bat detections: 6,701 (of 64,653 recordings). 

• Number of recorders with long-tailed bat detections: 20 (of 20 recorders; min = 121 recordings; max = 810 recordings).  

• Average number of long-tailed bat detections per detector-night (i.e., one detector operating for one night; to control for monitoring effort): 13.53 (± 32.66 SD). 

• Total number of bat-detector nights yielding long-tailed bat detections: 390 out of 495 detector-nights (i.e., 79% of detector-nights yielded bats). 

 What does this tell us?  

• Bats were active almost every single night during spring 2025!  

• Bats flew over the Glenorchy township almost every single night!  

• Bats were present throughout the Rees Valley — at least as far as Shelter Rock Hut!  

• Long-tailed bats probably aren’t as partial to the amazing coffee at Mrs. Woolly’s as we are (our recorder here yielded the lowest number of long-tailed bat detections, of the Glenorchy bat recorders). 

Glenorchy bat detections Nov-Dec 2025

We hope to continue monitoring our bats annually and will soon start to explore options for locating maternal roosts. If we can find the trees they are hiding in, we will do everything in our power to protect them!