Holding the same massed formation, the fowl in three or four broadening circles quickly attain a considerable altitude--say 100 yards--and then head away on their course, _ALWAYS_ (so far as they remain visible) to the _SOUTH-EAST_--diametrically opposite to the direction one would expect. As in deepening darkness we set forth on our homeward voyage, the heaven above pulsates at intervals with the beating of wings as yet more north-bound _corros_ pass overhead. Certain notable facts are observable in this vernal exodus. For upwards of twelve hours prior to departure the outgoing fowl take no food. That period is devoted exclusively to preparation and overhaul, _and_ to pairing. Plumage is preened and dressed till each unit is spick and span, speckless, and not a feather misplaced. All, moreover, are absolutely empty--in best and lightest travelling trim. When ducks are _acorrados_--that is, formed into _corros_ (the term is used thus in verb-form)--their normal watchfulness is relaxed. All thought and energy are concentrated on the impending event. Hence, at these periods they are apt to fall an easier prey to the fowler and on wholesale lines. The native gunners with their trained _cabresto_-ponies sometimes unite and enormous totals are secured as the result of a single joint broadside. The fowl thus obtained afford proof of the facts just stated, being all absolutely empty; besides which many different species will be killed at the one shot.[66] These men also state that the ducks start already paired and flying side by side; this, they say, explains the ferment and commotion of the previous hours--courting and sorting. Adult ducks, as previously indicated (p. 110), apparently pair for life; but since some species (such as wigeon) take at least two years to gain maturity, it is probable that the sexual phenomena which are so conspicuous in the _corros_ represent the first pairing of the newly adult two-year-olds. The most favourable time for the assembling of corros is on those days when great heat and calm at midday is succeeded towards evening by an extra strong sea-breeze. On such occasions very large numbers will leave between sundown and dark. Northerly winds will almost absolutely arrest the exodus. For the season of 1900-1901 our game-books showed a total of 4849 wildfowl (4674 ducks and 175 geese)--a record for which we were good-humouredly taken to task by our venerable friend the late Canon Tristram, who thought it looked excessive. The figures certainly are big, but the next entry in the book reads:-- _March 15._--This evening between fifty and seventy _corros_ left within half an hour--say 50,000 to 70,000 ducks. Next morning the marisma appeared as full as ever. Our toll of 5000 seemed by comparison but as a drop in the bucket! CHAPTER XXXIX SPRING-TIME IN THE MARISMAS BIRD-LIFE IN A DRY SEASON