Colonially nesting birds have been implicated in the destruction of their nest site vegetation, the most likely mechanism being through an overload or imbalance of soil nutrients. The numbers of egrets in coastal New South Wales colonies have increased rapidly in the second half of this century since cattle egrets {Ardeola ibis) were introduced. This species now nests colonially with three native species: great {Egretta alba), intermediate {Egretta intermedia) and little egrets {Egretta garzetta). Thus there is potential for more rapid degradation of the colony site. We measured the levels of phosphorus in surface seditnents, and phosphorus and nitrogen in water at eight colony site wetlands, and compared each to four other wetlands in the same region where there were no egret colonies. We conclude that levels of both nutrients were elevated in colony wetlands. The implications of this result for death of colony site vegetation and the conservation of the three native egret species are briefly discussed.
Better understanding of ecology is crucial for the success of endangered species conservation programmes. Little information is available on space use, conspecific interactions and recursions by one such species, the red panda Ailurus fulgens. To address this deficiency, we used GPS telemetry to examine their home range, core area, home-range overlap, dynamic interactions and recursive movement, and investigated the effect of sex, age and body mass on these behaviours across seasons. The median annual home range size was 1.41 km2, with nearly a quarter of this range being used as the core area. Sex and reproductive status were the key determinants of space use patterns on a seasonal scale, while body mass and age remained significant correlates for the core area. The home range of males was nearly double that of females, likely because of the polygynous mating system in red pandas. Females avoided overlapping home ranges, while males overlapped home range with up to 4 females, and neighbouring males overlapped nearly half of their ranges. We found rare interactions between males and females outside the mating season. Red pandas showed site fidelity within their territory, with seasonal variation across sex classes. We also observed high individual variation in patterns of both space use and recursive movement. Taken together, these results suggest that differences in biological requirements across seasons determine red panda space use patterns, conspecific interactions and recursion. However, forage availability and quality, climatic factors, disturbances and habitat fragmentation are also likely to influence these behaviours, and these factors need to be investigated.
Food supply is commonly regarded as ultimately controlling the size of bird
colonies. Most studies examining this problem have been on seabirds, and all
in the Northern Hemisphere. To search more widely for evidence of the
importance of food as a factor controlling the size of bird colonies, we
investigated egret colonies in a Southern Hemisphere region. We examined the
relationship between colony size and the area of potential feeding habitat
around each colony, compared with variables associated with the location and
the physical characteristics of each colony. All colonies (13 in total) along
800 km of coastline in New South Wales, Australia, were studied. Colony size
ranged from 7 to more than 2000 nests. There were very few correlations
between the number of nests and the areas of different types of feeding
habitat within 20 km of colonies. However, the available area of saltmarshes
proved to be a significant predictor of colony size for great
(Ardea alba), intermediate
(A. intermedia) and little egrets
(Egretta garzetta). Saltmarshes may be stable, long-term
feeding habitats for these three native ‘aquatic feeders’, but not
for the terrestrially feeding cattle egret (Ardea ibis).
Nest numbers of this latter species were related positively to the area of
saltmarshes, and negatively to latitude, suggesting that nest numbers of this
exotic species may be influenced by climate, with proximate factors such as
colonial nesting with the three native species also being important. Because
of the numerical dominance of cattle egrets, the numbers of nests of all
species followed the same pattern as that for cattle egrets.
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