Ravens killing our Mojave Desert Tortoises
By Joseph Douglas
The Mojave Desert Tortoise (Gopherus agassizii) is a remarkable creature that can live for up to 50 years in the wild if left to its own devices. Unfortunately, due to their inability to adapt well to the change in their environment, they have become officially endangered as of 2020. The creation of roads and many other man-made structures have changed the environment so much that it is making it hard for the tortoise to thrive. In contrast, man-made structures such as buildings and telephone poles are a great environment for the common raven the prime predator of juvenile tortoises. These ravens are classified as invasive species to the Mohave Desert. Before humans made the Mojave Desert a paradise for ravens, the ravens would migrate giving juvenile tortoises a chance to reach maturity which allowed them to survive better. This is now no longer the case as ravens have plenty of food and water from human intervention and have forgone migrating altogether. In the past it was said that you could see around 200 of these creatures per square mile in the Mohave Desert, now the number is averaged around 5–60.
Early Life of a Tortoise
We all know babies tend to be easy prey in the animal world and this goes double for tortoises. You see when the mom is done laying the eggs and burying them, she leaves. There is no parental care for baby tortoises, they are on their own from birth. Mom lays many eggs in the hope that some will survive. It takes about 5 years for a tortoiseshell to reach the strength to resist the sharp beak of the common raven. It also takes a minimum of 12 years for a tortoise to come to reproductive age.
Head-Start Help
Some great conservationists such as Mr. Daly have researched (Daly et al., 2019) if head-started baby tortoises stand a better chance of surviving to adulthood. It is considered accurate to say, that for a tortoise, size means better odds of surviving. So, Mr. Daly and his team set up some experiments to see if by head-starting the tortoise’s life, they could make the odds better for more tortoises to reach adulthood. The experiment was set up so that there would be 20 directly released tortoises, 20 outdoor reared, and 23 indoor reared. The idea was that the tortoises released in the beginning at birth would be the control group, where the outdoor and indoor head start tortoises would be released later after 7 months. They tracked the tortoises with radios they attached to their shell. To test their survival the tortoises were placed in spots that were parallel to a power-lined road that the researchers had seen ravens perched on. Furthermore, after release, they noted a mated pair of ravens nesting just 500 m from one of the release points. They would check on the tortoises regularly in the beginning, then once a week during winter. But once the tortoise started being preyed upon, they had to let nature do its thing without interference.
https://cal4wheel.com/latest-news/in-gear-feature-stories/842-raven-danger-the-desert-tortoise-is-just-the-beginning-of-an-ecosystem-in-jeopardy
Making a Difference is not Always Easy
I wish I could tell you that they all survived as it broke my heart to read the conclusions of this research article. Of the 68 released tortoise babies, 38 of them didn’t make it. With the lion’s share of the fatalities being from predation, mainly birds like the common raven. The experiment did not show sufficient evidence that head-starting these tortoises lead to a greater survival outcome on release at 7 months. It did show however that we can get these juveniles to a standard survival size promptly. From the time of birth to release, it took only 7 months for the indoor reared tortoises to reach the size of a typical 5–6 yr. wild juvenile tortoise.
Armed With Knowledge! What we can do
It is not all doom and gloom, as this experiment and others have shown the conservation community. We can make a difference in the lives of these tortoises. Speculation on if the size is not the only important factor to juvenile tortoises has been discussed. Further research into if survivability could have been increased with age as well. Tortoiseshell strength comes over time. This head-start research for tortoises is still in its infancy, many more breakthroughs will come with time. Now that conservationists have gained knowledge of possible tortoise weaknesses and are armed with the ability to now do these experiments in a timelier manner, we should see more efforts in the coming years to get these tortoise populations up. One of the things we as the common folk can do is control our waste. Animals such as ravens and small mammals can feed off our unprotected trash. This boosts the population of that species, and the prey of those species suffer for it. For more info on how to do that go to this website https://www.livingdesert.org/. For now, we will just have to be glad that our favorite desert reptile is now officially endangered. Hopefully, this will get the tortoise more recognition and consideration.
Work Cited
Daly, J. A., Buhlmann, K. A., Todd, B. D., Moore, C. T., Peaden, J. M., & Tuberville, T. D. (2019). Survival and movements of head‐started Mojave Desert Tortoises. The Journal of Wildlife Management, 83(8), 1700–1710. https://doi.org/10.1002/jwmg.21758
