Tree Squirrels Selectively Disperse High-Quality Acorns Away From Tree Trunks

Seed dispersal by scatter-hoarding rodents is key in shaping oak regeneration. However, the interacting effect of seed quality and foraging behavior on spatial dispersal patterns relative to trees remains poorly understood. We examined how the exotic Eastern fox squirrel (Sciurus niger) influences dispersal of Quercus agrifolia and Quercus lobata in Californian oak woodlands. Offering tagged acorns at camera-monitored stations, we quantified dispersal distances relative to both the supply station and the nearest tree trunk, a primary squirrel refuge, and assessed how acorn quality (weight and pre-dispersal insect infestation) influenced post-dispersal fate, embryo excision behavior, and dispersal patterns. Acorn weight did not affect post-dispersal acorn fate or embryo excision, but heavier acorns were dispersed over longer distances. Non-infested acorns were preferentially selected for embryo excision and dispersed farther than infested ones, particularly when partially eaten, indicating discrimination against low-quality seeds for storage. Post-dispersal fate further structured spatial patterns, as acorns were fully consumed near tree trunks, signaling rapid feeding in safe refuges, while non-eaten and embryo-excised acorns were transported farther away from tree trunks, likely to reduce pilferage. Oak species also shaped these patterns, with the more nutritious Q. lobata acorns being more frequently embryo-excised than Q. agrifolia. Additionally, excised Q. lobata acorns were dispersed farther. Overall, acorn dispersal by S. niger is context-dependent, driven by interactions among seed quality, tree trunk location, and foraging behavior. By selectively transporting high-quality acorns away from parent trees and refuges, this introduced squirrel promotes oak recruitment and woodland expansion.