Great Crested Grebe Begin to arrive on the lake in February. They breed on large, shallow inland lakes but prefer to winter on the coast, thus leaving in September. This bird has not had much breeding success at Vyrnwy due to the continually fluctuating water levels. The birds build their nest of reeds at the water's edge and too much rainfall and they get washed out, too little and they are left high and dry, so they build again. With the continual rainfall during the summer of 1998 they managed to breed successfully for the first time in ten years. This species has a wonderful courtship dance with the two birds 'mirror dancing' with weed in their beak as a token gesture. Between 3 and 6 pairs can breed on the lake itself.