Spatial behavior and habitat use of breeding mammalian females often change after parturition, reflecting not only the sharp increase in energy demands associated with lactation, but sometimes also limitations of a central place, if they return regularly to feed their altricial young. We conducted the 1st radiotracking study of habitat preferences of the pond bat (Myotis dasycneme), a threatened habitat specialist, comparing movements of breeding females during pregnancy and lactation in a lakeland zone of Poland. Pond bats are known to forage almost exclusively over water bodies. We predicted that 1) females commute shorter distances during lactation than during pregnancy, as they need to return to the colony during night to feed their young, and 2) pond bats select eutrophic lakes due to greater abundance of aquatic insects. The 1st prediction was confirmed, as pregnant females covered significantly longer distances between roosts and foraging sites (median 11.4 km) than lactating females (median 2.9 km). During pregnancy, bats foraged mostly over lakes and only rarely over rivers, using both habitats as available, but carp fishponds were selected. Lactating females selected rivers and canals but avoided lakes. The 2nd prediction was confirmed only in spring. Pregnant females selected eutrophic and avoided mesotrophic lakes, whereas during lactation, mesotrophic lakes were selected and eutrophic ones were avoided. This could explain the switch from chironomids, of smaller body size and found in eutrophic waters, to larger caddisflies, found in fast-flowing rivers, observed the diet of pond bats in a previous study. Lactating females may maximize their energy gain by shifting to large insects, thus obtaining larger portions of energy by a single capture effort. This study exposes the importance of small, relatively fast-flowing rivers in an energetically crucial period of the year for a species that has been perceived as associated with larger water bodies.