They do not work well with chilly nights and cool days as the syrup doesn't get warmed up enough. If you wait for a warm day and warm up the syrup they work fine. You could warm up the entire feeder's worth by putting it all in a pan and bringing it up to about 90 degrees or you could just take a saucepan full and boil it and pour it back in to warm up the rest. Or, empty it, flip it upside down and use it over some baggies.