RELATIONSHIPS BETWEEN FRUIT-EATING BIRDS AND SEED DISPERSAL IN URBANIZED AREAS

Abstract

Feeding ecology, of fruit-eating birds and seed dispersal were studied from Oct. 1976 to March 1978 in urbanized areas, eastern part of Tokyo and north-western part of Chiba Prefecture. The results of study with a special emphasis on the co-adaptative relation between fruits and birds were as follows.(1) Of 35 species of wintering birds observed in the study areas, the four species of Hypsipetes amaurotis, Sturnus cineraceus, Turdus naumanni and Cyanopica cyana were recognized to be most effective for fruit dispersal. These four species were middle-sized birds with an average of 50-100g in the body weight.(2) The population of three wintering species, H. amaurotis, S. cineraceus and T. naumanni increased from middle of Dec. to early Feb. at the Mizumoto Park, but at Kinshicho and Ichikawa the increase was occured at the beginning and middle of February. When H. amaurotis and S. cineraceus migrate from the Mizumoto Park in the rural area into the center of the urbanized area, the flock size of birds became smaller.(3) Seeds of species were found in the bird's droppings. The dominant species in seed (determined by the frequency of appearance more than 50% and number of seed more than 50 individuals) were Ligustrum lucidum, L. japonica, Ilex integra, I. crenata, Aucuba japonica, Paederia scandens, Sophora japonica and Cotoneaster horizontalis. The seed species eaten by birds were composed mainly of species planted in order to give the greenery and beauty in the urban environment. Some of them were climbing plants which were utilized frequently by fruit-eating birds as resting or foraging places.(4) A short distance dispersal of seeds within about 300 m was also observed. As tte foraging behaviour of wintering birds were disturbed in the urbanized areas, fruit-eating birds usually fly short distances around parent trees.(5) Almost all the seeds of species dispersed by birds germinate on May, and 70% of the seedings of L. lucidium were killed under dark or dry conditions by October.(6) From the relationship between the fruit size (shorter diameter) and the angle of mouth, four types of fruit size were classified.Type A: more than 25 mm. This type of species could not be swallowed but be pecked by fruit-eating birds. 5 species were observed.Type B: 10-15 mm. This type of species could not be swallowed effectively. 7 species were observed.Type C: 5-10 mm. This type of species was swallowed most effectively. 35 species were observed.Type D: 3-5 mm. This type of species was too small to be harvested effectively. 8 species were observed.H. amaurotis (the mouth size average=15.4±0.06, range 13.8-17.0mm, n=45) can swallow fruits of the type C effectively.(7) Attractive fruit colours such as red, black or orange occupied 92.2% of 52 fruit species. 70% of fruiting species had fruit clusters. They are attractive for birds, and make the fruit-eating bird to find out or harvest fruits effectively.