California Ground Squirrel Damage: Billions in Lost Crops, Feed, and Infrastructure

California's iconic ground squirrels, while a common sight, are a significant and costly threat to the state's agriculture and infrastructure. The damage they cause, from consuming crops to undermining essential structures, adds up to millions of dollars in losses annually. The problem is persistent, with data from various studies and historical records showing a consistent pattern of economic and physical destruction.

Economic Impact and Agricultural Losses

The financial toll of ground squirrel activity is staggering. An estimate from 1998 placed the annual agricultural economic damage in California at $20–$28 million. Adjusted for inflation to today, that’s approximately $53.76 million.

This figure is likely even higher today, as it doesn't account for other losses like damage to infrastructure and the cost of control measures. Studies show ground squirrels have a voracious appetite for a wide variety of crops. Historically, losses of 10–40% in almond crops were common, and some apple orchards lost over 50% of their yield.

In a modern context, high-value crops like pistachios, kiwis, and a variety of vegetables and melons are also heavily impacted. Ground squirrels can consume entire fields of crops like broccoli, as seen in a 2003–2004 field study in Santa Cruz County that documented 100% crop loss.

Forage and Feed Consumption

Ground squirrels are also formidable competitors for livestock forage, particularly in rangelands. A study from 2019-2020 found that each additional California ground squirrel reduced available forage by 27.2 kg per hectare. This can lead to significant feed shortages for cattle, especially during dry years when total forage is already low.

Forage losses can be substantial. For example, a density of 15 ground squirrels per hectare can destroy 900 pounds of forage, which is nearly equivalent to what a cow–calf pair consumes in a month.

The impact on forage is not a new problem. A study from before 1993 found that 355 Columbian ground squirrels could consume the same amount of forage in a single day as one cow. In Oregon, the problem is particularly acute, with 45% or more of the first cutting of alfalfa lost to ground squirrels in some areas.

The long-term effects of this competition are clear. A 1959 study showed that eliminating squirrels led to a 15 kg weight gain per heifer over a single season, highlighting the direct link between squirrel populations and livestock health and productivity.

Infrastructure and Safety Hazards

Beyond crop and forage consumption, ground squirrels cause extensive physical damage to agricultural and public infrastructure. Their complex burrow systems are a primary source of this destruction.

Burrow systems can weaken pond dams, levees, and ranch roads, creating a risk of collapse after 2–5 years of activity.

These burrow systems contribute to soil erosion, especially after seasonal rains, and can lead to dangerous sinkholes. Furthermore, the burrows pose a significant safety risk to livestock and farm equipment. Reports from multiple farming seasons detail damage to machinery when it collapses into burrowed ground. Livestock, particularly cattle and horses, risk broken legs from tripping over or falling into burrow entrances.

Finally, ground squirrels act as reservoirs for diseases like plague, posing health and safety risks to humans, livestock, and pets. These persistent threats underscore the need for effective and ongoing control measures to mitigate the billions in lost crops, feed, and infrastructure.

Sources:

Quinn, N., Baldwin, R. A., & Dimson, M. (2017). Ground Squirrel Best Management Practices Website-Expansion of Passive Extension Capacities (Final Report). University of California Agriculture and Natural Resources, UC Davis.

Controlling Ground Squirrel Damage to Forages and Field Crops, Ditches, and Dams EC 1429. (1997). Oregon State University. https://ir.library.oregonstate.edu/downloads/gm80hv565

Estimating Reduction in Standing Crop Biomass from California Ground Squirrels (Otospermophilus beecheyi) with Passive Extension Capacity. (2022). Rangeland Ecology and Management, 83(1).

Marsh, R. E. (1998). Historical review of ground squirrel crop damage in California. International Biodeterioration & Biodegradation, 42(2–3), 93–99. https://doi.org/10.1016/S0964-8305(98)00014-6

Gebhardt, K., Anderson, A. M., Kirkpatrick, K. N., & Shwiff, S. A. (2011). A review and synthesis of bird and rodent damage estimates to select California crops. Crop Protection, 30(9), 1109–1116. https://doi.org/10.1016/j.cropro.2011.05.015