Can small hornbills act as substitute seed dispersers for large hornbills?

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I studied hornbills in the tropical forests of Thailand, to understand their movement patterns and evaluate their effectiveness as seed dispersers. To estimate hornbill contribution to a particular tree species’ seed shadow I combined data from movements, determined by radio-tracking, with data from seed passage trials. Combining these data, I estimated that the median and maximum seed dispersal distances of small hornbills were shorter than those of larger species. Small hornbills are not able to alternate ecological roles with large hornbills, and thus loss of large hornbills may lead to reduce seed dispersal distances for many hornbill-dispersed plants in tropical forests.