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On the one hand I saw myself as an intruder, an unwelcome tourist in a foreign land. Later, Gary and his students conducted research on American Kestrels, building and placing about 375 kestrel nest boxes near Besnard Lake.

Inhibition of human platelet aggregation by N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine-HCl (DPPE), a novel antagonist of histamine binding, suggested that histamine might serve a critical role in cell function. Phorbol-12-myristate-13-acetate (PMA) or collagen was found to increase platelet histamine content in parallel with promotion of aggregation. Inhibitors of histidine decarboxylase (HDC) suppressed both aggregation and the elevation of histamine content, whereas DPPE inhibited aggregation only. In saponin-permeabilized platelets, added histamine reversed the inhibition by DPPE or HDC inhibitors on aggregation induced by PMA or collagen. The results indicate a role for histamine as an intracellular messenger, which in platelets promotes aggregation.

We describe a new estimator of population size that can be formed when independent sightings are made of marked and unmarked animals in a closed population where a subset of the population is individually marked. Each marked animal must bear a unique mark but the number of marked animals alive in the population is unknown. The estimate can be used when no recaptures or removals of animals are possible during the experiment. An example is estimating the number of immature bald eagles (Haliaeetus leucocephalus) on a lake some years after banding of nestlings. We derive the maximum likelihood estimates for population size and number of marks, and we show how to develop confidence intervals and perform goodness-of-fit tests. Criteria are developed for determining the number of sightings required to yield satisfactory estimates.

Bald eagle (Haliaeetus leucocephalus) densities vary throughout North America, but reasons for these differences are poorly understood and may be important for directing management practices. Thus, we evaluated the influence of forest nesting habitat and food abundance on the densities of bald eagles on 2 lakes in northcentral Saskatchewan, Canada. We found no evidence that nest-site availability influenced the number of eagles on either lake. Differences in the food supply were investigated both directly by netting fish, and indirectly, through information obtained from biological surveys at Besnard and Nemeiben Lakes. Cisco (Coregonus artedii), a key prey species for eagles, were more common and larger (P < 0.05) in Besnard Lake. Evidence from mineral content, plankton, benthic fauna biomass, and abundance of fish, support the contention that food abundance was the most important factor contributing to density differences of bald eagles between Besnard and Nemeiben Lakes. Food supply should be an integral part of any management plan aimed at protecting or enhancing bald eagle habitat.

In birds that exhibit sexual size dimorphism, hatching asynchrony, and siblicide, the probability of nestling mortality and the cost of rearing young may vary with different combinations of sex and hatching sequence. When food abundance varies spatially and temporally, parents may maximize their fitness by manipulating their primary sex ratio. We examined the sex and hatching order of nestling bald eagles (Haliaeetus leucocephalus) over 17 years on one lake and 5 years on another. The lakes are approximately the same size, but differ dramatically in eagle density and prey abundance. In years when the number of eaglets fledged was high (suggesting higher food abundance), there was a significant bias in the first-hatched chick toward the larger sex (females), and broods with a first-hatched male and a second-hatched female (MF broods) were under-represented. In years with lower productivity, and on the lake with lower food abundance, there was a male-bias in the population sex ratio of nestlings and the first-hatched egg. Variation in sex ratio and hatching order may relate to the probability of siblicide associated with MF broods, or the differential cost of raising the sexes.

An experiment was conducted during April and June 1978 to estimate aerial-visibility bias in searches for bald eagle (Haliaeetus leucocephalus) nests in northwestern Ontario, Canada. Randomly selected quadrats were searched independently by 2 separate teams of pilots and observers. Using either joint binomial probabilities or Petersen Index calculations, we estimated that approximately 76% of the nests or 85% of the breeding areas were found on a single search of shoreline. There were no differences (P > 0.05) in visibility due to season or observer, although undetected differences among observers may exist (i.e., type-II error). Aerial surveys of this type can be hazardous; 1 aircraft crashed during the project. Recommendations for standardized searches, and suggestions to improve safety are given.

An aerial census was conducted to determine the numbers and productivity, and to delineate distribution of bald eagles (Haliaeetus leucocephalus) in a 270,000-km2area of northern Saskatchewan. Randomly located sample units were designed to contain uniform amounts of primary nesting habitat. An estimated 3,900 breeding areas, 6,900 adults, 4,700 immatures, and 2,500 nestlings were present in the summer of 1974. In southwestern regions 0.95 young per breeding area were produced, indicating reproduction above the estimated minimum required for maintenance. There was a positive correlation between breeding area density and April mean temperature. Two models for eagle distribution in the province are discussed. As a monitoring tool, the census technique could detect a population change of 27%.

Particles with the density and enzymatic activity characteristic of known oncornavirus have been previously described in bone marrow cells from patients with leukemia in relapse and in remission. We have confirmed these findings and studied two patients in whom preleukemia was among the diagnostic considerations. Following cultivation of bone marrow from these patients for 1 week in conditioned media with dexamethasone, a high-speed pellet of the supernatant fluid and disrupted cells was prepared and analyzed on a sucrose gradient for enzymatic activity characteristic of RNA-directed DNA polymerase (reverse transcriptase). Peaks of endogenous DNA polymerase activity showing ribonuclease sensitivity and/or stimulation with the synthetic template poly(rC)· (dG)12-18were demonstrated in both patients at densities of 1.15 to 1.19 and 1.21 to 1.24 g/ml. Subsequently, diagnosis 2 and 4 months after initial evaluation revealed acute myelogenous leukemia and malignant histiocytosis, respectively. Prior studies have suggested a possible etiological significance of such particles in human leukemia. The demonstration of similar particles preceding clinically overt disease in these patients supports this hypothesis and offers the possibility of early diagnosis and treatment.