As always, a great blog from Aimee here for you , concentrating on understanding JUST WHERE DO ALL THE FEMALE ORANG-UTANS ROAM? Here she tells us how OuTrop have been working towards understanding more about the movement of orang-utans – something pretty hard to keep track of!..
|We see some amazing mothers
on our research grid. This is Cleo and infant this March.
“In orang-utans, while both sexes leave their natal home range, males and females have markedly different patterns of dispersal. Males actually disperse, where as females are “philopatric”, meaning their home ranges overlap (or branch off from) their mothers home ranges. Although both sexes move areas as they grow, it can not be said that both sexes disperse. Individuals move away from their parents when they reach the point that they become fully independent of their mother and this usually happens when they are around 9 years old (around 8 years old in Bornean orang-utans but 10 years in Sumatran orang-utans). The wide dispersal of at least the males is vital for the long-term persistence of a species to avoid inbreeding. Male orang-utans disperse far from their mother – their home ranges are thought to be very large, although we do not know exactly how large or how far they disperse from their natal area (one study’s data suggests that they disperse as far as 8km from their mother). Ben Buckley conducted his PhD at OuTrop and is currently analysing his data he spent the past two years collecting to answer these questions on male ranging patterns.Female orang-utans remain close to their natal area, establishing a home range adjacent or nearby the home range of their mother. This means that the home ranges of females will periodically shift as newly dispersed females establish a territory of their own and older females die. Understanding these changes allows us to find our study orang-utans with greater efficiency, so I’ve been hard at work mapping out the recent trends in the home ranges of the females on our study.As you may know from the blogpost of our last orangutan intern, Babs, part of our daily data collection when following orang-utans is taking GPS points and tracking our route. Sure, this helps us know where we are in the forest, but more than that it is the basis for mapping out the home ranges of the orang-utans we follow and the different tree species which they use in the forest. Each month we upload the data from the GPS unit onto a program on the computer (we use Garmin Mapsource) and from that I can then take the points and tracks from each date and save them under the corresponding orangutan for that day’s follow. This can be quite an arduous task, but it feels good when it’s finished! Once we have all of the follows individually saved, I then move the tracks from each individual in to a single document on mapsouce overlaying the most recent map of our grid system to see their home range. So far, the results are in for 2011 and 2012 only, but here are a few maps to give you an example of the results we have to date.
|Feb’s home range, 2011-2012|
These maps show you how females disperse to the area next to their natal area – their mothers’ home range. The map for Cleo (below) looks funny as it is data poor because she has been followed much less regularly the past few years, potentially a result of her shifting her home range further south meaning it is difficult to find her. It may be that whilst Feb and Indy have established home ranges next to hers, Cleo has been pushed out of her traditional home range a little.This makes searching a double-edged sword sometimes: the less we know about an individuals’ current home range the harder it is to find them, but the less we find and follow them the longer we are kept in the dark as to where they are ranging. I was lucky enough to stumble across Cleo at the end of March, and Santi, one of our local staff members, also found her early last month. Annoyingly, she was not in her nest and got lost in heavy rain on these two occasions so we still have very little recent information to help us find her.
Cleo’s home range, 2011-2012 (mother of Feb, sister or daughter of Indah)
Indy dispersed from her mother, Indah, just a few years ago. She has been followed extensively, so we don’t have to worry about a lack of data when interpreting this map: there is no question about it that Indy absolutely expanded her home range from 2011 to 2012. 2012 was the year that Indy gave birth to her first infant, Icarus, and perhaps the highly energetically demanding job of having an extra mouth to feed has made her expand her home range in search of a greater variety and quantity of food resources.
|Indy’s home range, 2011-2012|
Similar to Cleo’s, Indah’s map is a little data poor, which explains the gap in the range outline for 2012. We spent the whole of last month looking for her but to no avail. With her latest infant newly deceased, we are hoping that nothing bad has happened to her.
Indah’s home range 2011-2012 (mother of Indy)
Teresia is one of the few females on our study who’s DNA we are yet to analyse. We don’t know whether she is related to the other females, but seeing as she has a directly neighbouring home range I would imagine that she will be related to some degree. This map shows Teresia also shifting her range as Feb and Indy have consolidated and expanded theirs in the north of the grid. The data for 2013 will be interesting to add at the end of the year –we have already followed Teresia further west several times this year year, often taking us quite a way off the grid!
Teresia’s home range, 2011-2012
With these maps up on the orangutan identification boards at our camp in the forest, all of our staff and interns can clearly see the latest ranging patterns for our females and Luke, our senior primate scientist, and I can make informed searching strategies for finding a new focal based on this information. So far this year our study females have been doing a pretty good job at evading us – hopefully this will help us to find them more efficiently!”
Fantastic work from OuTrop and great to hear from Aimee (meet her here) on such exciting and current home range science. We’ll keep the blog updated with all our stories so make sure you bookmark our blog – maybe even a home page of OuTrop blog would be nice to wake up to! Find out all about us and help OuTrop here!