The information on heronries in India pertains mainly to a few regional studies (Mahbal, 1990, Nagulu and Rao, 1983, Naik et al., 1991, Naik and Parasharya, 1987, Parasharya and Naik, 1990, Santharam and Menon, 1991, Sharatchandra 1980, Singh and Sodhi, 1986), several site specific studies (Chaudhuri and Chakrabarti, 1973, Datta and Pal, 1990, 1993; Gee, 1960, Nagulu, 1983, Neelakanatan, 1949, Neginhal, 1983, Paulraj, 1984, Ragunatha, 1993, Ragunatha et al., 1992, Sanjay 1993, Subramanya et al., 1991, Subramanya and Manu, 1996, Urfi 1989c, 1990, 1992, 1993a,b; Vijayan, 1991) and a number of site records (Abdulali, 1962, Ali, 1960, Baker, 1935, Barnes, 1886, 1891, Barooah, 1991, Bates and ...view middle of the document...
, 1985 and Moller, 1987). Despite the costs, many hypotheses have been proposed to explain how colonial breeding may benefit the individual, but there is still little support for most of them and none appears compelling (Wittenberger et al., 1985 and Siegel- causey et al., 1990). Until the end of the 1980s, most discussions on how coloniality evolved were dominated by the two hypothetical advantages of enhanced food finding (Barta, 1995) and reduced predation (Wittenberger et al., 1985, Anderson et al., 1993 and Clode, 1993). By the end of that period, reviews concluded that avian coloniality is not a simple or unitary phenomenon and that not all breeding colonies are adaptive for the same reason. Recently however, new hypothesis involving habitat selection (Brown et al 1990, Shields et al., 1988,) and sexual selection (Mortan et al., 1990 and Wagner, 1993) set the stage for a general framework in the study of coloniality.
Data from a complex of alkali lakes in central North Dakota suggest survival of piping plover eggs and chicks may be diminished at relatively high density (Mayer 1991). Reproductive success of congeneric snowy plover (C. alexandrines) can be redced at high densities (Page et al. 1983). A large colony may benefit in terms of food acquisition due to increase in the number of breeding pairs that can provide information on food availability. Large colonies are believed to have a tendency to grow indefinitely. However excessive growth of a colony causes a decrease in the populations breeding rate due to intensive competition (Brown, Stutchburry & Walsh, 1990), mainly for nest sites (Parrish, 1995).
2.3 Temporal segregation:
Custer and Osborn (1978) found asynchronous nest building phases in north carollina. Maxwell and Kale (1977) found Florida Caerulea, started to breed later than other colony species. Frederick and callopy (1989) showed a strong difference for the nesting chronology of four species (Casmerodius albus, Egretta tricolour, Egretta caerulea, Edocimus albus) in florida. Maxwell and Kale (1977) and Jenni (1969) found that nests of Egretta thula and Bulbulcus ibis showed an average nest height from 2.04 – 2.59 m. result of this work support the notion that species overlap temporally in breeding, also segregate vertically in nest placement within the colony.
2.4 Central – periphery distribution of nests:
Breeding success may differ between centre and edge nests (Coulson 1968, Balda and Bateman 1972, Brown and Brown 1987), but it is not always attributable to predation (Coulson 1968, Bunin and Bates 1994). Nest defense against potential predators has long been suggested as an important force in the evolution of coloniality in birds (Lack 1968, Gotmark and Anderson 1984). Nests located in the more densely populated areas of the colonies are more sheltered from predation more than those at the periphery (Wittenberger and Hunt 1985). In the context of the relationship nest density and predation, the central –...