Deer in the Bustling Grove

By AdminBirds, Camera Traps, Conservation, Conservation Science Investigators, Education, Little Green Guards®, Mammals, Plants, Research, San Diego, USA
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Julian (Conservation Science Investigator) is making new discoveries in his camera trap research. This time his study takes us to an agricultural area bordering southern California coastal sage scrub, one of the endangered ecosystems in the United States. What wildlife species occur there? Read on.

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Written by Julian, Little Green Guards® C.S.I.

 

INTRODUCTION

After documenting the species that use the golf course behind my backyard, I moved on to another close by habitat for my C.S.I. project, an avocado grove.

Part 3 – Avocado Grove

The grove is located in an open space easement that was once coastal sage scrub habitat. As with my previous studies, I had some questions about the wildlife species I might find. My first question was: Are rabbits going to be found in the grove? My prediction was that they would not appear in the grove, or at least appear less frequently than in my backyard. I thought this because there is very little grass in the grove for rabbits to eat even though there are numerous bushes for them to hide. Another question I had was: Will there be more or fewer species than what I had documented in my backyard and on the golf course? My prediction was that there would be more species in the grove because it is a relatively large and undisturbed habitat with more diverse vegetation. Also, I thought the avocado trees might be a good food source for a variety of consumers1, 2.

 

METHODS

The avocado grove is located on a steep hill, less than a mile away from where I conducted my first two studies. Upslope the grove leads to a residential neighborhood, and downslope it ends at a reservoir.

 

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An aerial view of my current and past study sites (© LVDI International).

 

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I set up two camera traps about 200 feet apart along one of the terrace paths, under the canopy of the avocado trees (© LVDI International).

 

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Here I am testing one of the cameras to make sure it is working and that the field of view is as intended (© LVDI International).

 

The cameras were programmed as in my other studies, and I did not conduct any direct observations in the grove. The study period was from 7/8/20 to 7/13/20. As before I entered the data using Microsoft Excel, then I determined the number of independent events by species and created a graph. Using the independent event data I created another graph showing each species’ 24-hour activity pattern.

Additionally, to compare the differences in species occurrence among my three study sites I calculated the capture rate of each species (or class) at each site. The formula I used is:

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As you can see capture rates are standardized to 24-hour periods, whereas independent event data are actual counts. Lastly, I plotted three more graphs to illustrate the results at my three study sites.

 

RESULTS AND DISCUSSION

The cameras recorded 1,332 photos. Particularly, one camera took 1,143 photos, but most of them were false triggers caused by foliage shadows between midday and early afternoon. This is one of the things researchers need to watch out for when using camera traps in a forested area.

 

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The species recorded were: 1) striped skunk (Mephitis mephitis), 2) coyote (Canis latrans), 3) bobcat (Lynx rufus), 4) human (Homo sapiens), 5) mule deer (Odocoileus hemionus), 6) birds (shown here are two individuals of a small diurnal species), and an unknown (© LVDI International).

 

As predicted, I did not see any rabbits. Surprisingly, there were also no photos of rats, squirrels, opossums or raccoons, species that have been reported by local residents. The lack of these species could be due to the short monitoring period or because camera traps work best capturing medium sized mammals, so smaller animals may have passed by without being recorded.

The avocado trees provide a lot of cover, making it hard for birds like crows to fly in and out. That is likely the reason why I also didn’t see crows, which prefer more open spaces like the golf course.

One of the photos was very intriguing.

 

What could this two-legged animal be? At first glance I thought perhaps a Velociraptor had escaped from Jurassic Park! (Left © LVDI International, right © TarValanion)

 

Could the animal be V. mongoliensis, the first discovered species of Velociraptor? Or maybe it was V. osmolskae3? Finally, I had to think about what living species it could be. After careful observation I determined that this animal with large talons was most likely a great horned owl (Bubo virginianus), a species known to prey on rabbits, skunks and rodents on the ground4, 5.

In total I documented at least seven species in the grove. My hypothesis that there would be more species in the grove is confirmed since I found that there were six on the golf course and five in my backyard.

 

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Unlike my backyard and golf course studies, humans were not very common in the grove, with only one event. The three most sighted animals were coyotes, skunks and deer (© LVDI International).

 

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As before my data showed that human was active only in the daytime. One bird species was diurnal while the other was the nocturnal owl. Coyote, bobcat, skunk and deer were active at night although there was one incident when a coyote was observed during midday (© LVDI International).

 

It is interesting to note here that the three most commonly observed animals – coyote, skunk and deer – have very similar activity patterns. My camera trap results further revealed that they are similar in their feeding behavior.

Compared to both my backyard and the golf course, the avocado grove has much more food available that potentially could support many animals.

 

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The avocado fruit is highly nutritious and contains a lot of calories. Besides eaten by humans, it is also consumed by a number of animals. I noted some interesting behavior in a series of photos where a skunk ate part of a fallen avocado fruit, then a coyote bit a piece off the same fruit, and finally a deer took a few bites (left image from Pixabay, right © LVDI International).

 

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In my backyard, humans and rabbits had the highest capture rates, and on the golf course, birds (particularly crows) were most common, with humans being second once again. In the grove, the capture rates for skunks and coyotes were a lot higher than on the golf course, and the third highest rate in the grove, deer, had not appeared previously at all (© LVDI International).

 

My backyard is a small enclosed space with enough shelter, food, and water from the sprinklers for small herbivores such as rabbits to live. Even though there were no occurrences of skunks in my backyard, they probably do come as I’ve often smelled their scent in the morning. Perhaps skunks would have been recorded if the deployment period of the camera traps in my backyard was longer.

The golf course is a large wide-open area with little shelter and food, but is a good transitory space for animals with large home ranges, such as coyotes. Egrets are attracted to wet habitats where they can find food, like what I found on the golf course. If I had placed a camera at the bottom of the grove next to the reservoir I probably would have captured photos of egrets and other waterbirds.

The grove is a very large area mixed with avocado trees and wild plants. Because it connects to an area of coastal sage scrub, the vegetation is more complex than my other study sites. Even though there may be plenty of food and shelter for different types of consumers1, 2, many of the larger animals probably move freely and use both the grove and the natural habitat.

 

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The species I found in the grove are similar to those seen in the northwestern forests of North America6 (© S. Amsel).

 

What this tells me is that the open space easement is helping some native species to live alongside humans. I hope we will continue to maintain our environment to support a diversity of species.

This ends my three-part C.S.I. project. However, I decided to do one more project where I investigate a neighbor’s backyard that has no fence and backs up to the avocado grove. I look forward to more exciting discoveries. Stay tuned for when that uploads.

 

Sources:

  1. https://en.wikipedia.org/wiki/Consumer_(food_chain)
  2. https://peabody.yale.edu/sites/default/files/documents/education/Food%20Chains%20and%20Food%20Webs%20DF.doc
  3. https://en.wikipedia.org/wiki/Velociraptor
  4. https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=1865&inline=1
  5. https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=1866&inline=1
  6. Amsel, Sheri. “Temperate Rainforest Food Web” Exploring Nature Educational Resource ©2005-2020. October 19, 2020. http://www.exploringnature.org/db/view/Temperate-Rainforest-Food-Web

 

Julian is a 5th grade student in San Diego County.