1978 - 1979 
Dunson, W. A. (1982) Salinity relations of crocodiles in Florida Bay. Copeia . 1982(2):374- 
85. 
Studies were carried out to determine the importance of high salinity as a limiting 
factor to the Florida Bay population of Crocodylus acutus, since hatchlings in captivity 
are unable to survive in seawater. Sodium, K, Cl and osmotic pressure were measured 
in samples of plasma and cloacal fluid. The ion and uric acid content of solid cloacal 
excretions was also determined. Sodium influx and efflux of small crocodiles 
submerged in seawater and of isolated skin keratin were measured. The relationships 
between snout-vent length, body mass and surface area were estimated. It was found 
that the head-neck, tail, legs and body regions each account for about one-fourth of the 
total area. Studies were conducted on hatchling crocodiles of evaporative water loss, 
behavioral osmoregulation and on the water and ion content of possible food items. Wild 
hatchlings have a plasma osmotic pressure near 330 mOsm, a level typical of 
vertebrates. Body Na influx and efflux are quite low; there is a net uptake in seawater 
of about 9 mmoles 100 g' 1 body mass hr. The skin is probably very low in Na 
permeability. There is a substantial loss of water from fasting hatchling crocodiles 
submerged in seawater (35 %o) or held in moist air. Feeding is an important means of 
balancing these water losses. When fed fish ad lib. and kept in an aquarium divided into 
land and water portions, most small (100 - 480 g) crocodiles maintained body mass at 
salinities up to 17.5 %o. Some even gained mass at 26 %o. Field data from Florida 
Bay tend to confirm that C. acutus hatchlings are intolerant of 35 %o seawater. This 
study was conducted during 1978 and 1979. 
1978 - 1979 
Poole, A. (1982) Brood reduction in temperate and sub-tropical ospreys. Oecoloqia . 
53(1): 111-9. 
In an effort to understand patterns and causes of nestling loss in ospreys (Pandion 
haliaetus), the brood reduction in three eastern osprey colonies was studied during 
1978 and 1979. The colonies, located in Florida Bay (1) and on coastal Long Island, NY 
(2), differed in the average daily amount of food delivered to nestlings; Florida nests 
received 43% and 11% less fish per day than nests in the two NY colonies, largely 
because latitude and season restricted day length and thus foraging time for the winter¬ 
breeding Florida ospreys. Increased distance from stable food sources accounted for the 
lower rate of feeding at one of the NY colonies. Variation in clutch size in the three 
colonies reflected differences in latitude more than in food availability; average clutch 
sizes in Long Island were larger than Florida clutches by 0.5 of an egg, but were similar 
to each other and to those in other northeastern US osprey populations. Increased 
nestling loss coincided with reduced food delivery rates and, in food stressed colonies, 
this loss was 2-3 times greater than any recorded for ospreys. Starvation was the 
primary cause of nestling death, with mortality concentrated on third chicks, which 
hatched on average 3.9 days later and from eggs 5.6% smaller than chicks hatching 
first. Sibling aggression accounted for the preferential feeding of older nestmates, but 
only in colonies or nests where food was limited. Aggressive chicks nearly always 
stopped fighting after being fed. This behavior provided a reversible mechanism for 
controlling brood reduction that was based on nutrition. Growth rates of young 
measured during the first half of the growth period were more variable between 
colonies than within nests. This is interpreted as reflecting both the differences in 
colony food delivery rates as well as the evolutionary pressures of sibling competition 
to equalize the growth of nestmates. 
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