Making a Study of Bat Droppings.

Text By Brian Darnton (GB)

Images by Jan Parmentier (NL)

and Wim van Egmond (NL)


View bat with 3D specs


INTRODUCTION.
The subject of collecting anything so revolting as droppings might at first seem repugnant to the amateur microscopist, but I can assure you that it is a very compelling and interesting activity. Before becoming involved it's a good idea to contact your local bat experts who will acquaint you with the rules of law. These have been introduced to protect bats generally in the United Kingdom where some species are under threat. With a little good fortune a local organisation may even collect for you in a systematic manner. It's really a matter of laying a paper below the roost and storing the material in a desiccated condition month by month. The Pipistrelle is perhaps the most common bat to deal with.


CONTENTS.
The most pleasant aspect of this work is that unlike humans bats do not consume quantities of rubbish: all their food is caught on the wing in the air, though there is evidence of some preening, as bat hairs are a fairly common constituent of the droppings. The greater part of the food is pure insect matter.

Image right: facets of an insect's compound eye.

 

In May a dark colour will indicate an interest in the breeding beetles, a lighter colour in summer demonstrates an obsession with succulent moths. Many like the plume moths can be identified by their characteristic scales. In September when beetles again take to the air to find winter quarters the colour changes to dark brown again. The droppings become a pristine record of their diet.


PROCESSING.
The droppings can first be divided into the months of the bat year, and each sample can be cleaned and stored separately. The droppings are soaked in plain warm water in a 300 micron sieve and the sample is brushed and washed through to a 100 micron sieve that collects the sample and allows more convenient washing in warm water.

Image right: skin and hairs of an insect.

Brushing through the larger sieve breaks up the strings of matter cemented by mucus and natural secretions and greatly improves the quality and visibility of the strew as well as excluding the larger fragments. The washed insect parts can be removed from the sieve by a brush and stored in 50% iso-propyl alcohol in labelled tubes if not mounted at once.


THE STREW.
First the slide is treated with a small smear of gum tragacanth to cement the particles to the slide and prevent sinking if the slides are stored later on edge. A "00" art brush can be used to remove the debris from the sieve, and in a limited quantity of water the strew can be arranged with the brush to cover up to the 19mm ring mark on a mounting card.

Image right: trachea of an insect.

If the debris has been stored in the alcohol its a good idea to shake it up and pour it back into the sieve in order to counter the effect of uneven settlement. The slide is dried off and a few drops of Canada Balsam or Numount is applied before the cover slip is lowered. On a hot plate the strew should be hard enough after one day to be cleaned off and ringed with blackened Bioseal No. 2 using alcohol as a solvent if required. Do not neglect the labelling.


Skin cells


Skin pores


EXAMINATION.
In transmitted light the array of insect parts is usually extensive and sometimes quite spectacular. Smaller jaws, claws and hairs are well represented and tracheae are very common with their coils of spiral reinforcement. The hexagonal facets of the insect compound eye appear in many forms. There is a background scatter of moth scales which become more visible if the iris is closed down. The identification of parts can tax the expert equally as well as the amateur. Systematic collection week by week helps identification by eliminating the options to what is on the wing at any particular time period. In the Isle of Purbeck, the bat experts seem to be busy at the moment restoring many wild areas so that more flying insects become available to colonies under threat. Microscopy could help to confirm the improved diet.

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Published in the April 1999 edition of Micscape Magazine.

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