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Bats

The Woodrose and Short tailed bats.

 

Once common but now extremely rare, the native Parasitic Woodrose, (Dactylanthus taylorii) has so far been found on only two offshore islands, Codfish and Little Barrier (Hauturu), where the plant survives in a few places on ridges right at the top. Now fresh pollen from the plant has been  found by a Ph.D. student at 11 locations along 4 transects falling within a 1km square centred 1.5km NNW off the northern end of Okiwi airfield on Great Barrier. This provides an opportunity to find not only the plants but short-tailed bats and maybe some as-yet unknown invertebrates as well.

 

In the dark past, people dug up Dactylanthus and the associated portion of the host tree root. The Dactylanthus plant was removed by boiling, leaving behind  the intricately shaped root of the host tree. These were then cleaned and polished and displayed as a 'wood rose'.

 

Short-tailed bats will often make frequent nocturnal visits to lap up the aromatic nectar, and in the process transfer pollen between plants.

Before humans came to the island, short-tailed bats ploughed their way through and across the litter on the forest floor taking invertebrates, and nectar from selected plants that produced it. Now much reduced, they may well be holding on in such places as the Te Paparahi forest, or perhaps visit from Little Barrier or Coromandel. None have so far been recorded on Great Barrier. (A quarter or 900 of the world's mammal species are bats, and they are major pollinators of plant species world-wide, and in pre-human times not less so here).

 

Fortunately, it happens that the pollen is very large, and so must have been transported to Whangapoua by water rather than wind. (the student has also found a concentration of circa 400 year old pollen beneath the surface during her coring operations). The plant has a liking for parasitising the roots of a few native tree species such as rangiora,  mamangi, karamu, tutu,  hangehange, koromiko, mahoe, mapou, five finger, toro, and lancewood. These facts, and the preference for ridges, reduce the area and specific locations from which the pollen must have come to a watershed area of, say, 2 square kilometers north of Whangapoua. 

 

The time to search is when Dactylanthus sends up its nectar-laden flowers through the forest litter from late February to May. Unfortunately, rats and pigs also find them attractive, and the effect of both pigs and rats eating the woodrose flowers is to stain their guts a pinkish-purplish colour. So timely rat-trapping becomes a further indication of the plant's presence, although not necessarily their absence. 

 

Once found, cages open to bats but excluding other predators will be put in place over the plants, although such designs are experimental at this time.  

 

Ultrasonic bat detectors listening in overnight at 28KHz  near the flowering Dactylanthus, if or when found, will pick up the distinctive noise of short-tailed bats. If successful recordings are achieved, and it can be organised in time, the bats can be radio-tracked, raising the possibility of finding their roost or roosts, at which time an examination of the bat dung could show up invertebrates not before found here, as well as a rare wingless bat-fly associated with the bats.

 

There could, of course, be other locations for Dactylanthus around the island. 

 

Don Armitage

Subpages (1): Bats