20 THE SCOTTISH NATURALIST 
shore vegetation for their nests, the Grebes, Coots, and 
Waterhens in the outer fringes of the reed-beds, followed 
successively on the landward side by Sedge Warbler, Reed- 
bunting, Mallard, Pochard, Snipe, Redshank, Tufted-duck. 
Many of our smaller lochs of this type are in rapid process 
of silting up, and where this is the case the avifauna is a 
migratory one. The more aquatic species, such as Coot and 
Grebe, are crowded out first, and eventually disappear, to be 
followed by Water-rail, Waterhen, Sedge Warbler, and Reed- 
bunting, somewhat in the order named. When the silting-up 
process has proceeded far, the marsh becomes dominated in 
some cases by bog-myrtle, and a new colonist may appear 
in the form of the Grasshopper Warbler. Eventually, with 
a further drying up of the ground, the marsh flora entirely 
disappears, to be replaced by encroaching vegetation of 
the surrounding country, accompanied by its characteristic 
fauna. 
MARITIME ASSOCIATIONS. 
Prominent amongst these is the Sand-dune Association. 
The geological and botanical constituents are here arranged 
zonally to the tide, and a similar feature is presented by the 
avifauna. Proceeding from the shore inwards, we have a 
succession somewhat as follows: The region immediately 
above high-water mark, constituting the storm-beach, vary- 
ing according to geological conditions, consists of sand or 
gravel, scantily clad by plants, and in some cases with a 
prominent shell-zone. Here the first birds of the association 
appear in the Ringed Plover, and locally the Lesser Tern, 
the numerical status of the former modified in accordance 
with the abundance of pebbles, while the Lesser Tern appears 
to have its greatest settlements on beaches with a super- 
abundance of shells. The sandy beach is backed by the 
bare sand-dunes, populated in many instances by Common 
and Arctic Terns, the latter showing a tendency to settle on 
the lower edges of the dunes, and to encroach into the beach 
itself. On the landward side the dunes are invaded by the 
sand-binding marram grass, and in turn by a closer and 
more varied vegetation of scrubby heather and other plants. 
