Exploitation of Reedbeds by Specialist Passerines: Reed Parrotbill and Oriental Reed Warbler

Abstract

We studied exploitation of reedbeds by two specialist passerines, Reed Parrotbill (Paradoxornis heudei, listed as Near Threatened by the IUCN) and Oriental Reed Warbler (Acrocephalus orientalis), nesting in a tidal reedbed in the Changjiang River Estuary. Reed Parrotbills have significantly shorter, wider, and deeper bills than Oriental Reed Warblers. We distinguished >12 nest material categories in four groups (Phragmites, Zizania, artificial, and other) in nests of the two species. Reed Parrotbills used significantly fewer nest material categories, and had lower nest material diversity and a narrower nest material niche than Oriental Reed Warblers. More than 89% of the nest mass of Reed Parrotbills was Phragmites and was obtained from within the nesting habitat. More than 71% of the nest mass of Oriental Reed Warblers was Zizania from outside the nesting habitat. Most Phragmites material used by Reed Parrotbills was living tissue from reed leaf sheathes and stems. The large bill of the Reed Parrotbill facilitates exploitation of tissues from living reed shoots for nest materials, while the relatively long and slender bill of the Oriental Reed Warbler constrains it to use living reed shoots and exploit nest material from outside of nesting habitats. This is similar to their exploitation of food resources in reedbeds: Reed Parrotbills extract concealed insects within reed shoots while Oriental Reed Warblers glean exposed arthropods on a variety of plants. We confirm that food resource exploitation by Reed Parrotbills and Oriental Reed Warblers demonstrates a relationship between bill morphology and feeding as well as nest building.