. Wildlife and range research needs in northern Mexico and southwestern United States : workshop proceedings, April 20-24, 1981, Rio Rico, Arizona. Wildlife management Southwestern States Congresses; Wildlife management Mexico Congresses. Table 4.—Ratio, nesting sites, and productivity. Area Is. Conchas Zacatosa Piedra Chaparrito Punto Viejo Par. 28 Nesting site Ground Ground Small 4 ra above Approx. 4m 45 m shrubs sea level above sea above sea level level Adverse factors Gulls High tide Coyote None None None evident evident evident Productivity index chick 1 chick 0 chicks 0 1 chick
. Wildlife and range research needs in northern Mexico and southwestern United States : workshop proceedings, April 20-24, 1981, Rio Rico, Arizona. Wildlife management Southwestern States Congresses; Wildlife management Mexico Congresses. Table 4.—Ratio, nesting sites, and productivity. Area Is. Conchas Zacatosa Piedra Chaparrito Punto Viejo Par. 28 Nesting site Ground Ground Small 4 ra above Approx. 4m 45 m shrubs sea level above sea above sea level level Adverse factors Gulls High tide Coyote None None None evident evident evident Productivity index chick 1 chick 0 chicks 0 1 chick per nest per nest Productivity index less than Productivity - chick/nest. gull (Larus occidentalis) which starts reproducing in March, destroys the osprey eggs, attacks its chicks, and snatches their food from the young; it also chases the adult ospreys to force them to release their catch. We have observed these birds attacking osprey chicks, trying to peck their heads or trying to remove them from their nests to devour them. On Islote Piedra there are many nests, but very few are occupied, much less active. Kenyon (1946) and Reyes Osorio (1976) report preying activity by coyotes; in 1980 various nests produced eggs and chicks on the island, but none produced fledged birds. On Islote Zacatosa all nests but one were flooded by high tides. The nests built on towers had a higher productivity index than those of other areas; those nests are free from the activity of land predators, of high tides, and from attacks by gulls. The efficiency of nesting is higher, and a greater number of chicks is obtained. There is not much evidence of the impact of pesticides or other contaminants in the area of study. Spitzer et al. (1977) in their analysis of the DDE, PCB, and mercury concentrations in osprey eggs collected in different parts of. Figure 1.—Lagoon Complex-Ojo de Liebre and Guerrero Negro. 91. Please note that these images are extracted from scanned page images that may
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