64 



Ca.se 232 — continued. 



taken from various clutches, viz., House Sparrow (28), Robin(29), 

 Sparrow Hawk (30), Buzzard (31), and Lapwing (32), in which 

 the variations seen are probably due to the difference in age of the 

 parent of each egg. Eggs of the same clutch however, often 

 vary, i.e., clutch of Lesser Tern (33). Two complete clutches 

 of Lapwing eggs are also shown, one (32a) being all normal 

 in colour, whereas the other (32b) are abnormal in colour. But 

 perhaps the most striking example of the variations exhibited by 

 eggs, not only of the same species, but even of the same bird is 

 that of the Guillemot, in which no two eggs are quite alike. An 

 interesting series of these eggs may be seen in the Egg Cabinet 

 (Case 231, drawers 25 and 26). 



(c) Clutches. — 



The set of eggs which a bird lays for each setting is called 

 a clutch. The number of such a full clutch varies in different species, 

 from one to as many as twenty. In many groups of birds the number 

 of the clutch is constant and distinctive of the species. The following 

 examples are given : — 



One. Where a clutch consists of only one egg it is generally 

 large in comparison with the bird, i.e., Guillemot (34), Puffin (35), 

 and Stormy Petrel (36). 



Tivo. Two eggs clutches are very common and constant 

 Examples shown— Dove (37), Nightjar (38), Diver (39), and 

 Buzzard (40). 



Tivo to Three. Many birds are variable, sometimes two, some- 

 times three to the clutch, i.e.. Herring Gull (41), Kittiwake (42), 

 Skua (43) and Common Tern (44). 



Four. This is a very constant number among Plovers, etc., 

 i.e., Ring Plover (45), Sandpiper (46) and Common Snipe (47). 



Four to Seven. The Perching Birds are mostly included in 

 this series, i.e., Song Thrush (48), Greenfinch (49), Yellow Bunting 

 (50) and Swallow (51). A few however, as the Tits, lay as many as 

 ten or twelve eggs. 



Ten to Fifteen. Nearly all the Game Birds, Bails and Ducks, 

 lay from ten to fifteen eggs to the clutch, sometimes more. 

 Examples given are the Common Partridge (52) and Moorhen (53) 



The Cuckoo lays several eggs during the season, but only one 

 is deposited in each nest of the foster mother. For further account 

 of the Cuckoo see description of groups under Cases 159-161. 



