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Oiling Raven Eggs Cut Hatchability 94.5% and Raised Estimated Greater Sage-Grouse Abundance 44% Relative to Controls

Common raven at Ubehebe Crater in Death Valley, California
Conservation · Management

An experiment across sagebrush landscapes in Nevada, USA and California found that oiling common raven (Corvus corax) eggs sharply reduced raven reproduction while greater sage-grouse (Centrocercus urophasianus) performed better at the treatment sites. The study was first published on 5 August 2026 in The Journal of Wildlife Management.

Researchers compared egg-oiling treatment sites with control sites in a before-after-control-impact design. This approach asks whether the change from before to after treatment is larger at treated sites than the change over the same period at untreated controls, helping separate the treatment effect from broader changes over time. Raven eggs were coated with a non-toxic silicone oil that blocks gas exchange through pores in the shell. Treated ravens often continued incubating eggs that would not hatch. The authors point to prolonged incubation, the absence of food demands from chicks and fewer opportunities to renest as mechanisms that can reduce raven foraging pressure during the sage-grouse nesting season.

Raven reproduction and density declined

Across the experiment, oiling reduced raven egg hatchability by 94.5%. At the sage-grouse treatment sites, 28 of 29 treated raven nests failed completely, and raven density declined by an estimated 22% relative to control sites from before to after treatment.

Sage-grouse nest survival and abundance increased

The researchers monitored 749 sage-grouse nests from 2016 to 2022. At treatment sites, estimated nest-survival probability increased from 0.26 before egg-oiling to 0.58 during treatment years. Relative to the change at control sites, this corresponded to a 93% increase in nest-survival probability.

An integrated population model using data through 2023 also showed a population-level response. Estimated sage-grouse abundance increased by 44% at treatment sites relative to control sites from the pre-treatment to post-treatment periods. The authors conclude that raven egg-oiling produced strong and immediate effects on both ravens and co-occurring sage-grouse and may provide a targeted option where raven predation is a management problem, rather than relying on broader lethal control of adult ravens.

Sources and image credit

  1. Mathews, S. R., Sanchez, C. A., Coates, P. S., O'Neil, S. T., & Delehanty, D. J. (2026). Effects of oiling common raven nests on ravens and greater sage-grouse in sagebrush ecosystems. The Journal of Wildlife Management, 90(7), e70247. https://doi.org/10.1002/jwmg.70247Primary research article. Seven study sites in Nevada and California; raven egg-oiling reduced hatchability by 94.5%, sage-grouse nest survival increased 93% relative to controls and estimated abundance increased 44% relative to controls.
  2. Coates, P. S., Mathews, S. R., Sanchez, C. A., O'Neil, S. T., & Chenaille, M. P. (2026). Greater Sage-grouse and Common Raven Demographic and Count Data Before and After Egg-oiling Treatments of Raven Nests at Control and Treatment Sites [Data set]. U.S. Geological Survey. https://doi.org/10.5066/P148CV3MSupporting USGS data release containing raven nest, raven density, sage-grouse demographic and integrated population-model data used in the study.

Image: Wild common raven (Corvus corax) at Ubehebe Crater, Death Valley National Park, California, USA, 21 February 2014. Photo: Speednat / Wikimedia Commons. CC BY-SA 3.0. Representative species image; not a raven from the Nevada–California egg-oiling study. · CC BY-SA 3.0 · Source

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