An image is worth a thousand…pieces of information!
Are you familiar with the wildlife research methodology known as photo identification? Basically, it consists of taking pictures of the study species and recording the geographic coordinate for each of the pictures taken. These two smilingly simple items (pictures and GPS coordinates) can actually provide us with a ton of information about the study organism. This is one of the most commonly used methodologies in wildlife research because of all the information that can be obtained in a way that is least invasive to the animals.
This methodology is also referred to as “mark-recapture” because we are “capturing” in a photo the characteristics (or marks) that we can use to identify individuals. Recapture here does not mean we are actually capturing the animals, as this methodology does not require that. This is why photo-ID is a favorite non-invasive (and effective) approach to wildlife research.
We use photo-ID in our work with the common bottlenose dolphin (scientific name Tursiops truncatus) populations of Kino Bay, Mexico. During an outing, we search for dolphins in our study area and when we find them, we take their pictures, GPS coordinates, and make note of environmental (weather and water conditions) and behavioral information to supplement the information we obtain from the pictures. With good pictures, we are able to derive the following information:
- Identify each individual based on markings present in their dorsal fins. Dorsal fins of bottlenose dolphins are like a fingerprint in that not two are exactly the same. The shape, coloration, scars, presence of barnacles, and other features allow us to be able to tell individuals apart.
- The GPS coordinates allow us to track the whereabouts of individuals, which tells us if they are local, or travel around, or if they have a particular site they prefer the most. This is also useful when we see mothers with brand new calves, because it can help us determine if a site is an important nursery area for the species. Feeding locations can also be identified by the GPS coordinates together with behavioral information obtained from the sighting records.
- Social associations can be determined based on analysis of the dolphin networks. We can tell which individuals like to hang out in the same groups, and which individuals don’t hang out together at all. Sometimes a specific individual would link two or more groups of dolphins, which makes that individual key in maintaining groups connected. This is why removing dolphins from a population without doing a proper study of the importance of that individual can significantly impact the rest of the population if the individual removed is one of those key dolphins. This is true of other social wildlife species. In our study area of Kino Bay there are two different populations: one is a coastal ecotype (lives in shallow water regions) and the other is an oceanic ecotype (lives in deeper water regions).
- Mothers can be identified by the presence of calves. When the photo-ID study takes place over several years, we can also tell if the calves survive, which mothers have new calves and how long it takes for them to produce a new calf after the last one has weaned or perished. This information is also useful in determining how successful individual mothers are at contributing new individuals to the population.
- Calves can be tracked as they grow and we can know how old they are by the time they produce their first calf (in the case of females). This information tells us the approximate age of sexual maturity for the species, or at the very least the population in the study.
- Over time, mark-recaptures allow us to track how each individual moves about the study area, if they live in the area permanently, or if they are transient and only visit the area seasonally or sporadically. When scientists from different areas collaborate and share the pictures from their dolphin populations’ catalogs, a more comprehensive study of individuals’ roaming tendencies in a larger area can also be performed.
- Population estimates can be calculated based on the work of photo-ID. Because we know each individual we do not double-count them when estimating the number of dolphins in a sighting, and over time we can get an estimate of the size of the population.
- The overall health of individuals can be determined by looking at their appearance. Things like the presence of external parasites, scars from encounters with sharks, fights with other dolphins, fishing gear, boat propellers, or unidentified sources, as well as how well fed or emaciated they are (we can tell by how skinny they look and if their ribs are visible), are all indicative of the state of health of individuals. By tracking how often these characteristics are observed in a population we can determine if the rate of occurrence increases or decreases, which could be an indication of the state of the ecosystem over time.
These are some examples of all the information we can derive from taking photographs of dolphins and keeping track of GPS coordinates and environmental and behavioral data. However, a picture must meet certain quality criteria to be useful in a dolphin spatial-temporal study. Pictures that are blurry, have poor lighting or angle, or pictures where the whole dorsal fin is not visible, are inappropriate to reliably collect the information required. To take a good dolphin picture you must practice a lot! Dolphins move quickly, are very acrobatic, and move with agility in the water. Sometimes you only get a few seconds of their dorsal fin and so you must take their picture quickly, while making sure your zoom, lighting, and focus are all adjusted for the photo. We often take hundreds of photos in a day to make sure we get enough of the good ones to do our study. The process of sorting through the photos, identifying individuals, making sketches, and determining if we have recaptures can be tedious and time-consuming, and must be done with the utmost care to avoid mistakes. Not all out work is glamorous, but we love doing it anyway! 🙂
To see an example of how photo-ID works, see the images from our work exhibition at the Idea Museum (Mesa, AZ).
Incorporating drones into our photo-ID work
While the photos themselves provide a lot of information, they are also limited in how much we can determine with certainty. One example of this is how many individuals there are in a sighting. When the dolphin group we encounter only has a few individuals, we can be certain that we counted all of them. However, when the group is larger (and they can get to be in the hundreds!) then it is more difficult to estimate how many there are, and we might not get to take photos of all of them to compare against our size estimate. This is where a drone comes in handy. Drones have the birds’ eye view advantage and an image captured directly above the dolphin group can significantly facilitate our work in determining a size estimate, number of calves, etc. Additionally, photogrammetry (taking measurements based on photographs) can also help us better estimate health conditions based on the size of dolphins.
Another advantage to using drones is that we can follow and observe a group of dolphins remotely when they are underwater. Dolphins can hold their breath for several minutes at a time and in that time they can move quickly from one area to another. When the group goes underwater they can no longer be observed from the boat, unless we are in clear water conditions in shallow water. But since this is not often the case, a drone can help shorten the search time and allows us to observe the dolphins for longer periods of time while we obtain the information we need, which also includes observations of their behavior away from a boat. Of course, there are times when even a drone can’t find the dolphins. After all, they are masters in their element and conditions are not always conducive to us being able to keep a constant eye on them – but drones sure help!
Please note that the use of drones in the study of wildlife should be done by properly trained personnel. One thing is to know how to fly a drone, and another is how to fly it nearby wild animals. For the sake of their safety and yours, please do not attempt this unless you are properly trained and hold the required research or professional photography permits.
To see our fieldwork gallery, please click here.