A telemetric thread tag for tracking seed dispersal by scatter-hoarding rodents

Abstract

The seeds of many tree species are dispersed more than once, and this secondary seed dispersal is believed to enhance seedling recruitment. However, the effectiveness of secondary seed dispersal has rarely been assessed because it is difficult to track seeds until they die or germinate. We describe a new technique that uses thread tags attached to radio transmitters (telemetric thread tags) to track longdistance multistep seed dispersal by scatter-hoarding rodents. These telemetric thread tags can be turned off with a magnet and are reactivated when the seed moves. This method allows for seed tracking with minimal cache disturbance or distance bias, over long time spans, multiple seed movements, and with few effects on animal behavior. We used telemetric thread tags to track seed dispersal of the palm tree Astrocaryum standleyanum in a Neotropical forest, and achieved near-complete recovery of dispersed seeds tracked over distances as far as 241 m. We were also able to record the recovery time and fate of cached seeds without disturbing caches. Neither the removal rate nor the dispersal distance differed between seeds with telemetric thread tags and thread-tagged seeds. We conclude that telemetric thread tags can be used to document secondary seed dispersal by scatter-hoarding animals with unprecedented efficacy and precision. Given the size of these tags relative to the size of seeds and their dispersers, this method is applicable to the majority of tree species that are secondarily dispersed by scatter-hoarding mammals.

Evidence for cache surveillance by a scatter-hoarding rodent

“…Seeds were defleshed using a knife to resemble natural defleshing by rodents , air dried and given a 55 cm long 'telemetric thread tag' (Hirsch et al 2012b). Affixing thread tags to seeds is the widely accepted standard method for tracking seed dispersal by rodents because rodents will bury the seed but leave the thread above ground, allowing researchers to locate the seed (Forget & Wenny 2005).…”

“…Affixing thread tags to seeds is the widely accepted standard method for tracking seed dispersal by rodents because rodents will bury the seed but leave the thread above ground, allowing researchers to locate the seed (Forget & Wenny 2005). Telemetric thread tags consisted of a 30 cm black nyloncoated stainless-steel leader wire tied to a 4.1 g cylindrical VHF transmitter (Advanced Telemetry Systems Inc., Isanti, MN, U.S.A.) with a 20 cm antenna (Hirsch et al 2012b). When seeds were buried, the transmitters affixed to the ends of the wire remained above ground, thus allowing us to place the transmitters on top of magnets that deactivated the transmitter and saved battery life.…”

“…When seeds were buried, the transmitters affixed to the ends of the wire remained above ground, thus allowing us to place the transmitters on top of magnets that deactivated the transmitter and saved battery life. When the seed was moved by an agouti or other animal, the transmitter was activated, allowing us to find the new location of the seed with hand-held radiotelemetry equipment (for full details see: Hirsch et al 2012b;Jansen et al 2012). We covered the transmitter and flagging tape with loose leaf litter to reduce possible visual cues.…”

“…These caches were made by nine of the 16 tagged agoutis. As soon as we found the location of the cached seed, we mounted a camera onto a nearby tree or a U-shaped metal rebar pushed into the ground at w1.5 m distance from the cache (Hirsch et al 2012b). To scale the scene, we then placed two pieces of rope (5 m long), marked with tape every 20 cm, in a cross formation on top of the cache location, took a picture with the camera and removed the rope.…”

Dispersión de semillas de Mauritia flexuosa (Arecaceae) por frugívoros terrestres en Laguna Azul, Beni, Bolivia

“…Dasyprocta dispersa y entierra las semillas hasta 60 m desde los parentales (Tuck-Haugaasen et al 2012); aunque alcanza distancias extremas de > 200 m (Hirsch et al 2012a). Este comportamiento de acopio esparcido o "scatterhoarding" (Morris 1962) cumple un rol importante en la dispersión de las semillas (Alho 1982;Jansen et al 2004;Jorge y Howe 2009).…”