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New Method for Tracking Animal Movement

A fresh approach improves accuracy of animal home range estimates.

Jack Hollins, Christen Fleming, Justin M. Calabrese, Les Harris, Jean Sebastien Moore, Brendan Malley, Michael Noonan, William F. Fagan, Jesse M. Alston, Nigel Hussey

― 5 min read


Revolutionary Tracking Revolutionary Tracking Technique Revealed movement studies. New method enhances accuracy in animal
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When we study animals, one of the big questions is where they like to hang out. This area, known as their home range, is crucial for understanding how they pick their favorite spots for food, friends, and avoiding danger. Recently, scientists have been using electronic tracking to follow animals around and see where they go.

There are many ways to figure out how big an animal's home range is, but each method comes with its own quirks and limitations. Some common methods are geometric estimators, which use shapes based on where we saw the animals, and probabilistic methods, which assume a model based on randomness when determining the home range.

One popular probabilistic method is called Kernel Density Estimation (KDE). This method places little "bubbles" around each location where an animal was seen. When you add these bubbles together, they form an estimate of the home range. The size of these bubbles depends on a feature known as bandwidth. A narrow bandwidth creates a more tight-knit home range, while a wider bandwidth can stretch the home range out, leading to less accurate results.

However, things get tricky when animals encounter Barriers they can't cross, like cliffs or busy roads. In these situations, the home range estimates can spill out into areas that the animal doesn't actually use, which can lead to inflated home range sizes - a problem called spillover bias. Imagine if a snail's home range included the road just because it crawled next to it once; that wouldn't be a fair estimate!

To fix these overestimates, various approaches have been designed. Some methods try to include ecological factors, like food availability, while others make adjustments after the home range is created. Unfortunately, many of these methods are complicated, resource-heavy, or have their own issues.

New Way to Estimate Home Ranges

Enter a new approach called locally corrected AKDE! This method aims to solve the spillover problem by adjusting the bubbles around animal locations before they create the final home range. This way, if an animal was seen just next to a boundary, the estimates won’t overreach into unusable areas.

For example, imagine our curious snail again. If it spends some time next to a big rock, instead of including the area beyond the rock in its home range, the new method will adjust the estimate so that it only includes areas it can actually access. This makes the home range calculations more accurate and useful.

Using computer simulations, researchers tested how well this new method works compared to older correction techniques. They found that the locally corrected method produced more accurate home ranges than traditional methods, especially when animals were close to barriers. It was like giving our snail a clearer map of where it can crawl without accidentally including the neighbor's garden.

Testing the Waters

To really see how this new method performs, researchers used fake animal tracking data with known boundaries and compared the results. They ran simulations that tracked animals for various lengths of time, adjusting how they moved relative to barriers.

In these trials, the researchers found that locally corrected AKDE consistently provided better estimates of home ranges compared to traditional methods. It was a bit like having a GPS that correctly tells you where to go instead of leading you on a wild goose chase through uncharted territories.

The researchers also applied this method to real-world data gathered from lake trout in two very different lakes. They saw that the locally corrected method once again produced more reliable home range estimates than older methods. It was like discovering that while both methods could get you to the lake, only one would show you the best fishing spots!

What About Those Barriers?

It's important to note that not all animals behave the same way near barriers. Some might "bounce off" and change direction, while others might follow along the barrier closely. The new method can handle these different behaviors better than previous approaches.

For instance, if our snail was just chilling next to a rock, the new approach makes sure it doesn’t accidentally include a whole field in its home range just because it once slid over to the edge. This gives a more realistic picture of where the snail actually prefers to hang out.

Summary of Local Corrections

In summary, while there are many ways to guess where animals roam, the locally corrected AKDE offers significant improvements. It takes away the guesswork and helps provide a clearer view of animal movements. This method shows great promise for future studies, ensuring that scientists can better understand not just how far animals travel, but more importantly, where they truly feel at home.

Using this improved approach, researchers can more accurately track animal behavior and make better decisions when it comes to conservation and management efforts. Who knew that accurately mapping a snail's home could reveal so much about its life and the environment around it?

With the use of these methods, wildlife experts can now craft better strategies for protecting animals and their habitats, ensuring that we can all share the planet - humans, snails, and everyone else.

So next time you see an animal, remember it might just be as complex as balancing on a fence or crawling along a rock. They have their own homes, likes, and dislikes, and with the right technologies, we're getting better at understanding them every day!

Original Source

Title: Home range spillover in habitats with impassable boundaries: Causes, biases, and corrections using autocorrelated kernel density estimation

Abstract: O_LIAn animals home range plays a fundamental role in determining its resource use and overlap with conspecifics, competitors and predators, and is therefore a common focus of movement ecology studies. Autocorrelated kernel density estimation addresses many of the shortcomings of traditional home range estimators when animal tracking data is autocorrelated, but other challenges in home range estimation remain. C_LIO_LIOne such issue is known as spillover bias, in which home range estimates do not respect impassable movement boundaries (e.g., shorelines, fences), and occurs in all forms of kernel density estimation. While several approaches to addressing spillover bias are used when estimating home ranges, these approaches introduce bias throughout the remaining home range area, depending on the amount of spillover removed, or are otherwise inaccessible to most ecologists. Here, we introduce local corrections to home range kernels to mitigate spillover bias in (autocorrelated) kernel density estimation in the continuous time movement model (ctmm) package, and demonstrate their performance using simulations with known home range extents and distributions, and a real world case study. C_LIO_LISimulation results showed that local corrections minimised bias in bounded home range area estimates, and resulted in more accurate distributions when compared to commonly used post-hoc corrections, particularly at small-intermediate sample sizes. C_LIO_LIComparison of the impacts of local vs post-hoc corrections to bounded home ranges estimated from lake trout (Salvelinus namaycush) demonstrated that local corrections constrained bias within the remaining home range area, resulting in proportionally smaller home range areas compared to when post-hoc corrections are used. C_LI

Authors: Jack Hollins, Christen Fleming, Justin M. Calabrese, Les Harris, Jean Sebastien Moore, Brendan Malley, Michael Noonan, William F. Fagan, Jesse M. Alston, Nigel Hussey

Last Update: Nov 30, 2024

Language: English

Source URL: https://www.biorxiv.org/content/10.1101/2024.11.20.624379

Source PDF: https://www.biorxiv.org/content/10.1101/2024.11.20.624379.full.pdf

Licence: https://creativecommons.org/licenses/by-nc/4.0/

Changes: This summary was created with assistance from AI and may have inaccuracies. For accurate information, please refer to the original source documents linked here.

Thank you to biorxiv for use of its open access interoperability.

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