The Hoarding Features Of Squirrels In Urban Green Area During Autumn And Winter

Squirrels(Sciurus vulgaris) settled in urban green as these of wild animals adapted to the urban environment, formed different features of activities from that in the wild. From October 2012 to January 2015, a series of experiment were carried on in the autumn and winter to investigate the hoarding features of squirrels in urban green area, include behavior observation and caches investigation. Experimental investigation were carried out in urban green areas where squirrels inhabited inside Harbin City. We took measure of tagged seeds(pine nuts) as squirrels’ cfood to investigate the labeled caches, so we can analyze the features of food hoarding and caches retrieval. The results are as follow:Squirrels inhabited in urban green did behave hoarding behavior, retrieving behavior and re-hoarding behavior. Squirrels in urban green played scatter hoarding. The scatter caches of squirrels contained different amount of pine nuts. The maximum number of pine nuts in the caches is 17. The amount of caches which contained five pine nuts is the maximum. The squirrels disperse large amounts of caches around food source without a direction. The space density of caches spatial distribution differed to the distance to the food source. The space density of caches spatial distribution max at the area located between 5m and 15m from the food source. The squirrels’ hoarding intensity peaked in this area. Beyond this area, the longer distance to food source, the lower space density of caches as well as hoarding intensity.In urban green the squirrels behaved retrieving behavior mostly in winter. Our investigation took advantage of the concept of retrieval rate to describe the feature of cache retrieval. In the environment of urban green with food supply, the cache retrieval rate of squirrels was about 35.39%. In autumn and winter, with stable food supply the squirrels might retrieve one third of their caches in urban green. After cache retrieval, the food item of the cache would be dispose as below:1.eatting the food item; 2.eatting part of the food item and re-hoarding another part; 3.re-hoarding the food item. In the autumn and winter of urban green, close to 20% of caches would be disposed as eating the food item or re-hoarding the food item by squirrels, less than 3% of caches would be disposed as eating part of the food item and re-hoarding another part.Our investigation evaluated the cache re-hoarding and cache eating by the concept of re-hoarding rate and eating rate. Under food supply, in urban green the re-hoarding rate of squirrels’ caches was about 21.18%, and the eating rate was about 21.53%. The food item of the cache might be hoarded twice or three times. In the autumn and winter of urban green, about 1.92% of the food items were hoarded twice, nearly 0.32% of the food items were hoarded three times. The squirrels might eat a quarter of their hoarded food for one autumn and winter.We made fake cache to test the impact of olfaction on squirrels’ retrieving behavior. In the urban green area, about 21% of the fake cache could be retrieved by squirrels with the help of olfaction. Compared this result with the retrieval rate in autumn and winter urban green, we concluded that the dependence rate of squirrels’ retrieving behavior on olfaction is about 60%. We replaced the food items of caches with paraffin-enveloped seeds to test the impact of spatial memory on squirrels’ retrieving behavior. In the urban green area, the retrieval rate of paraffin-enveloped caches was about 12.80%. We compared this result with the retrieval rate in autumn and winter urban green, we got the conclusion that the dependence rate of squirrels’ retrieving behavior on spatial memory is about 35%.