The herons and bitterns Ardeidae comprise some of the largest birds encountered during nocmig and consequently they have some of the lowest pitched NFCs. They all have flight calls and, with some exceptions, they use them mainly at night. For some species, especially the bitterns, it is rare to see a bird while it utters its flight call because it will nearly always be too dark. Most herons also use their NFC as a daytime flight call on the way to, eg, feeding grounds. As they also feed at night, make sure you are well away from a heronry, or better, any water body, if you hope to count actual passing migrants. Typically, herons and bitterns spread out in all directions just after breeding, which is referred to as post-nuptial dispersal, and this also takes place at night. Due to this, it is difficult, if not impossible, to discern between a dispersing bird and one on a longer journey to its wintering grounds, when we hear heron NFCs at night.