Differences in feeding behavior of Eurasian Tree Sparrows Passer montanus in winter

Abstract

We used high-definition photography to investigatee fruit-feeding behavior of Eurasian Tree Sparrows Passer montanus. Using a digital video camera equipped with a super-telephoto zoom lens, observations were conducted in the Iwai area of Moroyama, Saitama Prefecture, from mid-January to mid-February 2022. Our study revealed that sparrows use two behavioral types to feed on fruits. The first type is hulling, when sparrows used their beaks to remove the outer coverings of the fruit and then swallowed only the fruit. Sparrows used this method to feed on Asian cultivated rice Oryza sativa, Amur silvergrass Miscanthus sacchariflorus, southern crabgrass Digitaria ciliaris, and Japanese panicgrass Panicum bisulcatum. The second type is chewing, when the sparrows broke down hard pericarp or bracts of the fruits by rotating fruits on the tongue and crushing them between the tongue and upper palate. This chewing type was further categorized into two types based on subsequent observed actions. The first was sorting swallowing, in which sparrows selected and discarded broken hard pericarps and seed coats, or involucres, and swallowed only the remaining edible parts. The sparrows used this method to feed on Japanese hop Humulus japonicus, giant ragweed Ambrosia trifida and cobbler's pegs Bidens pilosa var. pilosa. The second one was non-sorting swallowing, in which the sparrows swallowed all parts of fruits without discarding broken pericarps and seed coats. The sparrows used this method to feed on Japanese panicgrass Panicum bisulcatum and pale smartweed Persicaria lapathifolia. In the case of green amaranth Amaranthus viridis, the sparrows exhibited two actions: they initially removed the pericarp, then chewed and crushed the seed, or they swallowed them intact. In some instances, they discarded a piece of seed coat after chewing.