Patterns of seed dispersal by flying frugivores in Hong Kong
Abstract of thesis entitled
PATTERNS OF SEED DISPERSAL BY FLYING FRUGIVORES IN
Jacqueline E. S. Weir
for the degree of Master of Philosophy
at The University of Hong Kong
in March 2004
Seed dispersal is a critical process in forest regeneration, particularly in degraded landscapes. In Hong Kong most seed dispersal is carried out by a small number of frugivore species. The main aim of this study was to quantify the pattern of seed dispersal by the most important flying frugivore, the light-vented bulbul (Pycnonotus sinensis). Seed shadows were predicted for this and three other common frugivores: the red-whiskered bulbul (Pycnonotus jocosus), hwamei (Garrulax canorus), and dog-faced fruit bat (Cynopterus sphinx).
Gut passage times for seeds were measured in newly captured and long-term captive birds. Median times until first appearance of a seed were 14-20 minutes in the two bulbul species and 37 minutes for hwameis. Median times until the last appearance of seeds from multi-seeded fruits were 36-38 minutes for bulbuls, with some retained over 100 minutes, and 61 minutes for hwameis, with some retained over 150 minutes. Movement patterns were measured by attaching tail-mounted radio-transmitters to birds caught in mist-nets and using triangulation to locate them every 10 minutes. These were then used to calculate how displacement from an arbitrary starting point, representing a fruiting shrub or tree, increased over time. The displacement-time graphs and gut passage data were combined to produce estimates of seed dispersal distances.
Predicted median seed dispersal distances were typically 40-50 m for adult light-vented bulbuls in winter, 100-200 m for juvenile light-vented bulbuls in summer, 100-150 m for juvenile red-whiskered bulbuls in summer, 30 m for adult hwameis in winter and 30-40 m for juvenile hwameis in summer. Bulbuls occasionally moved over 1 km within the gut passage time for seeds. Dog-faced fruit bats had median dispersal distances of 150-200 m, based on gut passage times from the literature, and maximum movement distances up to 900 m.
Range analysis for the species studied, and visual observations of movements by frugivorous birds were carried out in order to modify the symmetrical predicted seed shadows in terms of the heterogeneous real landscape. Non-breeding light-vented and red-whiskered bulbuls appeared to be nomadic and willing to cross open areas, although they appeared to prefer forest and shrubland. Hwameis were sedentary and very rarely crossed open areas. Light-vented bulbuls were most willing to use isolated perches in open areas. Movements within grassland and shrubland were increased during fruiting peaks of the shrubs Rubus reflexus and Eurya spp. Dog-faced fruit bats had varying range sizes and crossed open lowland areas, but willingness to enter upland degraded sites needs investigation. Bats dispersed cultivated and native fruit species. Seed shadows for small, defecated seeds may be diffuse, but for the larger seeds dropped under feeding roosts would be patchy.
Management actions to encourage seed dispersal into degraded areas should consider landscape features used by these species and the distances they are willing to travel. The provision of suitable perches should increase seed input to open areas and the attractive nature of fruiting shrubs could be utilised in planting strategies.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:frugivores china hong kong seeds dispersal
Date of Publication:01/01/2005