Characteristics of birch trees which influence Yellow-bellied Sapsucker (Sphyrapicus varius varius) feeding activity.

It has been commonly held that sucrose amounts and sapflow rates are mechanisms for tree species preference for Yellow-bellied Sapsuckers (Sphyrapicus varius varius). Previous studies suggest that sapsuckers preferentially select larger birch trees (>20 cm dbh) as feeding trees. I tested whether large birch trees were being selected as feeding trees through sapwell frequency measures. I also collected birch phloem sap samples from 11 different trees to find if variability existed between different sizes of trees in terms of sap flow rates and sucrose percentage of sap. My results suggest that larger birch trees are not being preferentially selected as feeding trees. On the basis of sampling procedures for tree size preference, I suggest that different methods of sampling should be taken due to the serious biases that result from sapwell frequency counts. I also found that sapflow rates and sucrose percent of sap measures do vary between different sizes of birches. It was found that there is a significant inverse relationship between sapflow rates and sucrose percent versus dbh. This relationship to dbh suggests that smaller birches are more preferable and could be used to account for preference within birches.