birds' excrement. They'll be tilling small plots of vegetation 

 to see the effects. And, they may even attempt to create 

 "artificial" bushes for the birds to use while destroyed 

 vegetation grows back. 



The biologists will be manipulating the habitat in the 

 hope of producing a more stable, long-term environment for 

 the birds, says McCrimmon. 



The management possibilities include maintaining the 

 habitat for herons and egrets as well as developing a habitat 

 for ground-nesting birds such as least terns, brown pelicans 

 and laughing gulls, says McCrimmon. That may mean 

 planting hardier vegetation for the herons and egrets, or 

 changing the substrate in a way that will attract the ground 

 nesters. 



i 6 T T T e'd like to make Battery a place where a variety of 

 VV birds could find a safe place to nest for a long 

 period of time," says McCrimmon. "There's a tendency for 

 colonies like this to come and go. The real challenge is to 

 make the colony suitable for 25 years or more." 



For example, terns and gulls may nest for only two to five 

 years on an island before its vegetation changes and they 

 move on to another island. But some wading birds will use 

 the same island for as long as 25 years. 



Not all the birds on Battery live in harmony and 

 McCrimmon says they may eventually choose to exclude 

 some species from nesting. For example, fish crows nest 

 among the herons and eat about half of the eggs which the 

 white ibises lay. Mark Shields, one of Parnell's graduate 

 students and the Audubon warden on Battery Island, found 

 that fish crows are able to get the ibis eggs, regardless of the 

 density of the vegetation where the birds nest. 



The crows are greedy; they take many more eggs than 

 they can eat, says Shields. 



Parnell says the fish crows are one pressure on the birds 

 they may decide to eliminate. For example, they might try 

 to manipulate the vegetation in such a way as to reduce the 

 crow population by making the site less desirable to that 

 species. 



If fish crows don't get the eggs, the birds face possible 

 predation from the black-crowned night heron. Those birds 

 go after the young of the other species and feed the baby 

 birds to their own. 



Such predators get help from cattle egrets which arrive at 

 Battery Island later in the season, when the other 

 species have already begun to nest. They disrupt the nesting 

 birds, leaving the young vulnerable to predation. 



About two weeks after the young birds hatch from the 

 egg, they venture from the nest. This is when they are most 

 vulnerable to people. As a sanctuary, Battery Island is off- 

 limits to visitors and, as warden, Shields has the authority 



to enforce that rule. It is particularly crucial to avoid 

 human intrusion during the nesting weeks, says Parnell. 



The birds may also find themselves at the mercy of the 

 weather, says Parnell. "Timing is critical. A storm can be 

 very damaging to young birds. All the nests may be 

 destroyed or the birds may be beat to death by hail." 



McCrimmon points out that, to some extent, the hazards 

 which face the birds — predation from other species, over- 

 fertilization of the vegetation, and exposure to bad 

 weather — are all part of a natural system of checks and 

 balances in the population. But the Audubon Society hopes 

 to help the birds maintain a balance on Battery Island. If 

 they succeed, the birds will return. If nature takes her 

 course, the birds may destroy their own home and go in 

 search of another. 



— Nancy Davis 



White ibis hatchling peers from its nest 



Adult white ibis, a wading bird 



