The native western gray squirrel (Sciurus griseus) and introduced fox squirrel (Sciurus niger) can be found occupying various locales in southern California (USA) either coexisting or living separately. Since the introduction of the fox squirrel in 1904, there have been local extinctions of gray squirrels in parks and natural areas in urban and suburban locations. Little research has focused on the coexistence of these two species with no work with an in-depth focus on their behavior. The objective of this study was to observe the daily activity of gray and fox squirrels in areas where they coexist and those they occupy alone to determine if the presence of the fox squirrel is negatively impacting the behavior of the gray squirrel. Focal animal observations were conducted using the instantaneous sampling method in three habitat types: coexistence, gray squirrel only, and fox squirrel only. Daily activity related to self-maintenance, communication, feeding, and the location in which the animals were observed were recorded within 15-min observations of individual squirrels. There was no negative impact from the fox squirrels; however, there were behavioral similarities among the species when coexisting which suggests niche overlap. An overlap in the use of space and time in shared habitats can be detrimental to the already declining population of gray squirrels in urban and suburban habitats, particularly in times when environmental conditions are less than ideal and resources are less abundant.

本土西部灰松鼠 ( Sciurus griseus ) 和引进的狐松鼠 ( Sciurus niger )) 可以在南加州（美国）的不同地方找到，它们要么共存，要么分开生活。自 1904 年引入狐狸松鼠以来，在城市和郊区的公园和自然区域中，灰松鼠已经局部灭绝。很少有研究集中在这两个物种的共存上，没有深入关注它们的行为的工作。本研究的目的是观察灰松鼠和狐松鼠在它们共存的区域和它们单独居住的区域的日常活动，以确定狐松鼠的存在是否对灰松鼠的行为产生负面影响。在三种栖息地类型中使用瞬时采样方法进行焦点动物观察：共存、仅灰松鼠和仅狐松鼠。与自我维护有关的日常活动，交流、喂养和观察动物的位置在 15 分钟内对个体松鼠的观察进行记录。狐松鼠没有负面影响；然而，当共存时，物种之间存在行为相似性，这表明生态位重叠。共享栖息地中空间和时间使用的重叠可能不利于城市和郊区栖息地中已经减少的灰松鼠数量，特别是在环境条件不理想和资源不太丰富的时候。当共存时，物种之间存在行为相似性，这表明生态位重叠。共享栖息地中空间和时间使用的重叠可能不利于城市和郊区栖息地中已经减少的灰松鼠数量，特别是在环境条件不理想和资源不太丰富的时候。当共存时，物种之间存在行为相似性，这表明生态位重叠。共享栖息地中空间和时间使用的重叠可能不利于城市和郊区栖息地中已经减少的灰松鼠数量，特别是在环境条件不理想和资源不太丰富的时候。