I have worked on plotting the observed values of speed and turning angle for each bird versus the time of the day, to see if any of the patterns observed in the Incremental Autocorrelation plots can be traced back to relationships between the individual points. As far as I can see, there doesn’t seem to be none. I am attaching the output for four of my birds, including also an image of the area where they have been moving (where green is forest and pink is agricultural land).
(Note: The point plots correspond to a single day of observations, while the autocorrelation ones were made using all the observation days. I couldn’t run the analysis with the data from single days because they weren’t enough to meet the minimum required by the tool. )
I am thinking that I should do the same type of plot using distance in the X axis rather than time, because there’s not a strict direct relationship between distance moved between two points and time taken to move that distance. Thus, a 30-second time interval between two points could either be reflecting 10 meters or 100 meters.
My new dilemma is that I am not sure what that distance on the X axis should represent. The distance of all points to an arbitrary point (e.g.: site of capture)? The distance along a movement path defined by joining consecutive points? Suggestions are welcome!
Forgive me for being slow to understand… if you can tell me a bit more about your data, I will try to recommend some analytical strategies. For example, you have point features I see… does each point have a particular bird’s ID or a species ID or ? I’m guessing you have a timestamp for each point ? … and perhaps an attribute that tells you what type of terrain the bird is over at each point ? For each point it seems you have an attribute reflecting speed ? What does the rotation value at each point refer to? You said something suggesting this is actually line data (from/to points)?
Lauren
Hi Lauren,
thanks for your interest in my question.
My data consists of location points from a radiotelemetry study. I worked with 20 individuals of a single species of hummingbird (all the points are associated to a particular bird’s ID). I have the coordinates of each point and also the time and date when they were taken. Having this information I was able to calculate the speed at which the bird travelled (calculated for each point as the distance to previous point over time taken to move between points).
The data on the type of habitat associated to each point (forest or non-forest) is being extracted from a GIS layer).
I also created a line layer from my point layer by joining consecutive points. The rotation angle refers to the angle between two consecutive movement lines (i.e., lines joining point A to B and B to C) and often used to characterize animal movement as it gives an idea if an animal was moving in a more or less straigth line or going back over its steps. Similarly, speed can indicate if a bird was using an area just as a transit zone (non stop movement,high speed) or potentially for other activities (eg: stopping to feed, low speed). My hypothesis is that the birds will move at lower speeds and show more tortuous paths when they are inside the forest, and move in straight , “fast” lines when moving across an open area (where they have no resources) and was hoping that the behavior of the autocorrelation graph would reflect patch sizes.
What do you think?
Thanks again!
Noelia