Spatial patterns of mistletoe seed deposition are behaviorally determined by frugivorous birds but the effects of gut passage on mistletoe seed germination has received little attention. Here we investigate the effects of several predictors and passage through the digestive tube of two bird species, Grey Silky-flycatcher (GSF, Ptilogonys cinereus) and Cedar Waxwings (CW, Bombycilla cedrorum) on seed germination of Psittacanthus schiedeanus (Loranthaceae). Fruits were collected from mistletoe plants growing on three host tree species, Liquidambar styraciflua, Acacia pennatula, and Rapanea myricoides. More mistletoe seeds from Liquidambar trees germinated than those from Acacia and Rapanea trees, regardless of fruit treatment. Fewer seeds defecated by GSFs germinated compared to those defecated by CWs or manually extracted. However, analyzed within a generalized linear modeling framework, host source and seed weight were the best predictors for the occurrence of germination. Seeds were retained longer in the guts of GSFs than seeds in those of CWs, and increased retention time reduced significantly mistletoe seed germination. This study demonstrated that gut passage affected seed germination responses of mistletoes of P. schiedeanus, and additional studies should examine this relationship for other mistletoe-bird interactions.
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Vol. 136 • No. 3