Osprey Population Research Articles

North American Osprey Populations and Contaminants: Historic and Contemporary Perspectives

Osprey (Pandion haliaetus) populations were adversely affected by DDT and perhaps other contaminants in the United States and elsewhere. Reduced productivity, eggshell thinning, and high DDE concentrations in eggs were the signs associated with declining osprey populations in the 1950s, 1960s, and 1970s. The species was one of the first studied on a large scale to bring contaminant issues into focus. Although few quantitative population data were available prior to the 1960s, many osprey populations in North America were studied during the 1960s and 1970s with much learned about basic life history and biology. This article reviews the historical and current effects of contaminants on regional osprey populations. Breeding populations in many regions of North America showed post-DDT-era (1972) population increases of varying magnitudes, with many populations now appearing to stabilize at much higher numbers than initially reported in the 1970s and 1980s. However, the magnitude of regional population increases in the United States between 1981 (first Nationwide Survey, ∼8,000 pairs), when some recovery had already occurred, 1994 (second survey, ∼14,200), and 2001 (third survey, ∼16,000–19,000), or any other years, is likely not a simple response to the release from earlier contaminant effects, but a response to multi-factorial effects. This indirect “contaminant effects” measurement comparing changes (i.e., recovery) in post-DDT-era population numbers over time is probably confounded by changing human attitudes toward birds of prey (shooting, destroying nests, etc.), changing habitats, changing fish populations, and perhaps competition from other species. The species' adaptation to newly created reservoirs and its increasing use of artificial nesting structures (power poles, nesting platforms, cell towers, channel markers, offshore duck blinds, etc.) are two important factors. The timing of the initial use of artificial nesting structures, which replaced declining numbers of suitable trees at many locations, varied regionally (much later in the western United States and Mexico). Because of the increasing use of artificial nesting structures, there may be more ospreys nesting in North America now than ever before. Now, with the impact of most legacy organic contaminants (DDT, other organochlorine [OC] pesticides, polychlorinated biphenyls [PCB], polychlorinated dibenzo-p-dioxins [PCDD], polychlorinated dibenzofurans (PCDF]) greatly reduced or eliminated, and some osprey populations showing evidence of stabilizing, the species was proposed as a Worldwide Sentinel Species for evaluating emerging contaminants. Several emerging contaminants are already being studied, such as polybrominated diphenyl ethers (PBDE) and perfluorinated acids and sulfonate compounds (PFC). The many advantages for continued contaminant investigations using the osprey include a good understanding of its biology and ecology, its known distribution and abundance, and its ability to habituate to humans and their activities, which permits nesting in some of the potentially most contaminated environments. It is a top predator in most ecosystems, and its nests are relatively easy to locate and study with little researcher impact on reproductive success.

Incidence of organochlorine pesticides and the health condition of nestling ospreys (Pandion haliaetus) at Laguna San Ignacio, a pristine area of Baja California Sur, Mexico

We identified and quantified organochlorine (OC) pesticide residues in the plasma of 28 osprey (Pandion haliaetus) nestlings from a dense population in Laguna San Ignacio, a pristine area of Baja California Sur, Mexico, during the 2001 breeding season. Sixteen OC pesticides were identified and quantified. α-, β-, δ- and γ-hexachlorocyclohexane, heptaclor, heptachlor epoxide, endosulfan I and II, endosulfan-sulfate, p,p'-DDE, p,p'-DDD, aldrin, dieldrin, endrin, endrin aldehyde, and endrin ketone were the OCs found in the plasma of nestlings, ranging from 0.002 to 6.856 pg/μl (parts per billion). No differences were found in the concentration of pesticides between genders (P > 0.05). In our work, the concentrations detected in the plasma were lower than those reported to be a threat for the species and that affect the survival and reproduction of birds. The presence of OC pesticides in the remote Laguna San Ignacio osprey population is an indication of the ubiquitous nature of these contaminants. OCs are apparently able to travel long distances from their source to the study area. A significant relationship between hemoglobin and mean corpuscular hemoglobin concentrations and OC concentrations were found suggesting that a potential effect on the health of chicks may exist in this osprey population caused by the OC, e.g. anemia. The total proteins were positively correlated with α-BHC, endosulfan I, and p,p'-DDD. It has been suggested that OC also affects competitive interactions and population status over the long term in vertebrate species, and our results could be used as reference information for comparison with other more exposed osprey populations.

Morphometric sex determination of young Ospreys Pandion haliaetus using discriminant analysis

Capsule Discriminant functions based on morphometric variables provide a reliable method for sex identification of free‐living and hacked young Ospreys. Aims To describe an easy, accurate and low‐cost method for sex determination of fully grown nestling and fledgling Ospreys Pandion haliaetus based on morphometric measurements. Methods Four different measurements were taken in 114 birds (40–73 days old) and a DNA analysis, using PCR amplification, was carried out for sex identification. A forward stepwise discriminant analysis was performed to build the best explanatory discriminant models, which were subsequently validated using statistics and external samples. Results Our best discriminant function retained forearm and tarsus as the best predictor variables and classified 95.1% of the sample correctly, supported also by external cross‐validations with both hacked and free‐living birds. Moreover, a discriminant function with only forearm as predictor showed a similar high correct classification power (93.4%). Conclusions These discriminant functions can be used as a reliable and immediate method for sex determination of young Ospreys since they showed high discriminant accuracy, close to that of molecular procedures, and were supported by external cross‐validations, both for free‐living and hacked birds. Thus, these morphometric measurements should be considered as standard tools for future scientific studies and management of Osprey populations

Osprey Diet Composition and Quality in High- and Low- Salinity Areas of Lower Chesapeake Bay

Chesapeake Bay, in the northeastern United States, is believed to support the largest concen- tration of breeding Ospreys (Pandion haliaetus) in the world. Following the banning of DDT, this popula- tion exhibited significant spatial variation in growth rates, with the fastest and slowest rates occurring in the lowest and highest salinity areas, respectively. Because salinity can influence fish distributions, we quanti- tatively analyzed Osprey diet composition along the gradient in the Chesapeake Bay to determine if variation in foraging ecology contributed to this pattern of population recovery. We recorded .1800 hr of food-provisioning behavior for 25 pairs within nine study areas that were classified as either upper estuarine (,5 parts per thousand (ppt) salinity) or lower estuarine (.18 ppt). Atlantic menhaden (Bre- voortia tyrannus) and seatrouts (Cynoscion spp.) were dominant dietary components for pairs within lower- estuarine reaches, whereas gizzard shad (Dorosoma cepedianum) and catfish (Ictaluridae) dominated upper- estuarine diets. Lower-estuarine prey fish averaged 6% shorter (Kolmogorov-Smirnov test: D 5 0.203, P 5 0.004), 34% lighter (D 5 0.305, P , 0.001), and 40% lower in energy content (D 5 0.247, P , 0.001) than their upper-estuarine counterparts. We conclude that diet quality may be contributing to spatial variation in the growth rate of the Chesapeake Bay Osprey population.

Distribution pattern of an expanding Osprey (Pandion haliaetus) population in a changing environment

We studied the nest site selection and distribution pattern at landscape level of the German Osprey population, and demonstrated how to test the predictions of the ideal free distribution theory and its derivatives on such an expanding population. Information about the location and breeding success of each Osprey nest site between 1995 and 2005 was collected through a long-term monitoring programme. Data of land cover types were acquired from the administrations of each federal state and the CORINE Land Cover database. The results showed that Ospreys preferred landscapes with more water bodies and forests. Such sites were also occupied earlier and had higher local population density. However, in the study period of 11 years, there was a gradual shift from forest-dominated landscapes to agricultural land-dominated landscapes. The breeding success increased over time, with no difference in the breeding success between pairs nesting on trees and poles, whereas there was higher breeding success at nest sites surrounded by more agricultural land and less forest. The more efficient foraging in eutrophic lakes in agricultural landscapes was the most likely cause for the higher breeding success. The distribution pattern of the Ospreys did not match the resource allocation, which deviated from the models tested. We suggested that the proximate cues used for nest site selection mismatched site quality due to anthropogenic environmental changes.

PCDDs, PCDFs, PCBs, OC pesticides and mercury in fish and osprey eggs from Willamette River, Oregon (1993, 2001 and 2006) with calculated biomagnification factors

The osprey (Pandion haliaetus) population nesting along the main stem Willamette River and lower Santiam River was first studied to evaluate contaminants and reproductive rates in 1993 when 78 occupied nests were present. By 2001, the population increased to 234 occupied nests, a 13.7% annual rate of population increase. A sample egg was collected from each of a series of nests along the Upper River (river mile 55-187) in 1993, 2001 and 2006 to evaluate trends of persistent contaminants (organochlorine [OC] pesticides, polychlorinated biphenyls [PCBs], polychlorinated dibenzo-p-dioxins [PCDDs], and polychlorinated dibenzofurans [PCDFs]). Nearly all OC pesticide residues decreased significantly, e.g., p, p'-DDE (DDE) from 2,350 to 1,353 to 210 microg/kg wet weight (ww). PCBs followed a similar pattern over time, e.g., SigmaPCBs 688 to 245 to 182 microg/kg ww, while PCDDs and PCDFs showed a more precipitous decline (often 85-95%) between 1993 and 2001, with no egg analyses warranted in 2006. During 2001-2002, sample osprey eggs were also collected from nests at three Headwater Reservoirs and two lower reaches (Newberg Pool and Tidal Portland) of the Willamette River, as well as the lower portion of the Santiam River to evaluate spatial residue patterns. Significant differences were seldom detected among the different sampling areas for OC pesticides (probably due to small sample sizes), although higher concentrations were often seen in the lower reaches, e.g., DDE 901 microg/kg ww (Headwater Reservoirs), 1,353 (Upper River), 1,384 (Newberg Pool) and 2,676 (Tidal Portland). PCB congener concentrations in eggs were usually higher in the Tidal Portland reach than at other locations and often significantly higher than at the Headwater Reservoirs or Upper River. Mercury (first analyzed in eggs in 2001), PCDDs and PCDFs were extremely low in 2001/2002 with no significant spatial patterns. Whole fish composite samples of largescale sucker (Catastomus macrocheilus) and northern pikeminnow (Ptychocheilus oregonensis), which account for about 90% of the biomass in the diet of this osprey population, were also collected from the Willamette River in 1993 and 2001 and analyzed for the same contaminants as osprey eggs. Contaminant residues in fish from the Upper River decreased between 1993 and 2001, paralleling findings for osprey eggs. Likewise, spatial patterns for fish residues paralleled findings for osprey eggs from the different reaches in 2001. A second empirical estimate of biomagnification factors (BMFs) from fish to osprey eggs for OC pesticides, PCBs, PCDDs and PCDFs (ww and lipid weight [lw] basis) was calculated based on residue data collected in 2001. The two independent BMF estimates (1993 and 2001) for each contaminant from the Upper River provide a measure of consistency, e.g., DDE (ww) 87 and 79, (lw) 103 and 112; SigmaPCBs (ww) 11 and 8.4, (lw) 13 and 12. Mercury did not biomagnify from fish to osprey eggs (BMF = 0.60). Legacy contaminants investigated had limited (perhaps only DDE), if any, effects on reproductive success of the increasing osprey population nesting along the Willamette River by 2001.

Density dependence in a recovering osprey population: demographic and behavioural processes

1. Understanding how density-dependent and independent processes influence demographic parameters, and hence regulate population size, is fundamental within population ecology. We investigated density dependence in growth rate and fecundity in a recovering population of a semicolonial raptor, the osprey Pandion haliaetus [Linnaeus, 1758], using 31 years of count and demographic data in Corsica. 2. The study population increased from three pairs in 1974 to an average of 22 pairs in the late 1990s, with two distinct phases during the recovery (increase followed by stability) and contrasted trends in breeding parameters in each phase. 3. We show density dependence in population growth rate in the second phase, indicating that the stabilized population was regulated. We also show density dependence in productivity (fledging success between years and hatching success within years). 4. Using long-term data on behavioural interactions at nest sites, and on diet and fish provisioning rate, we evaluated two possible mechanisms of density dependence in productivity, food depletion and behavioural interference. 5. As density increased, both provisioning rate and the size of prey increased, contrary to predictions of a food-depletion mechanism. In the time series, a reduction in fledging success coincided with an increase in the number of non-breeders. Hatching success decreased with increasing local density and frequency of interactions with conspecifics, suggesting that behavioural interference was influencing hatching success. 6. Our study shows that, taking into account the role of non-breeders, in particular in species or populations where there are many floaters and where competition for nest sites is intense, can improve our understanding of density-dependent processes and help conservation actions.

Metal concentrations in osprey (Pandion haliaetus) populations in the Florida Bay estuary

Mercury and trace metal contamination is a concern in the Florida Bay estuary, but the effects on biological pathways are not very well understood. The analysis of mercury and trace metals (beryllium, vanadium, chromium, cobalt, nickel, copper, arsenic, cadmium, antimony, and lead) was conducted on tissues of adult and juvenile osprey (Pandion haliaetus) to examine the bioaccumulation and distribution in Florida Bay. Mercury concentrations were found at levels associated with decreased reproductive success, and no significant differences were found between adult and juvenile samples. Concentrations of other trace metals were generally below levels known to cause environmental problems. Mercury levels were particularly high in birds from central and eastern Florida Bay. In addition to mercury, vanadium was the only trace metal that showed significant geographic variation. Mercury concentrations in adult samples were comparable to levels reported in adult osprey from two other sites in North America, but concentrations in juvenile tissues were higher in Florida Bay. Although ospreys are a potential biomonitoring species for mercury contamination, further inter-population comparisons are needed, as well as additional information about the risks associated with bioaccumulation.

Two-Year-Old Nesting Behavior and Extra-Pair Copulation in a Reintroduced Osprey Population

ABSTRACT A reintroduced population of Ospreys (Pandion haliaetus) in eight counties surrounding Minneapolis/St. Paul, MN was monitored from 1984–2005. We recorded the behavior of marked birds at 306 occupied nests. Two-yr-old Ospreys were involved in nest attempts more often than previously reported. Twelve were observed; eight of these (five males and three females) occupied nests, and the remaining four were floaters. Readily available nest sites and abundant food resources may have been factors in breeding attempts by these young Ospreys. Age at first known occupied nest averaged 4.13 yr for males (N = 38) and 3.36 yr for females (N = 11). Age at first known successful nest averaged 4.39 yr for males (N = 38) and 3.64 yr for females (N = 11). In 2003, two 2-yr-old males fledged chicks. We also observed Ospreys copulating with more than one partner in the same breeding season on 14 occasions (10.52% of nests where eggs were laid). All but one extra-pair visit was observed between 2003 and 2005, ...

Distribution and status of the Osprey (Pandion haliaetus) in South Australia

The breeding population of Ospreys (Pandion haliaetus) in South Australia was estimated at ∼52 pairs in 2005. These were sparsely distributed (one pair/30.1 km of coastline) from the eastern Bunda Cliffs in the west of the state, to Kangaroo Island in the east, with most of the population on western and southern Eyre Peninsula in the Great Australian Bight region. Most nests were constructed on broken sections of coastal cliff and near-shore rock-stacks, with a small number on man-made structures and one active nest in a tree. The population is geographically isolated, with the westernmost territory in South Australia ∼1000 km from the nearest known breeding sites to the west, in Western Australia, the nearest population to the east is in north-eastern New South Wales, >1500 km distant. There is evidence for an overall population decline in South Australia as only historical breeding records were found for upper Spencer Gulf and for the Murray River indicating a substantial reduction in range. In addition, some nesting sites on Eyre Peninsula and Kangaroo Island are considered vulnerable to disturbance from unmanaged coastal recreation and the encroachment of residential and tourism development.

Reproductive activity in the Osprey (Pandion haliaetus) on Kangaroo Island, South Australia

This study reports on aspects of the breeding biology of Ospreys (Pandion haliaetus) on Kangaroo Island from data collected over 18 breeding seasons between 1985 and 2004. Over this period an average of nine pairs were located each year, and a total of 145 occupied territory years were monitored for breeding activity and outcomes. Of these, active breeding occurred in 103 (71%), with 60% of these successfully fledging young. Productivity was found to average 0.66 young fledged per year per occupied territory, and 0.92 young fledged per year per active nest. This level of productivity, while similar to that of other studies in Australia, is below the minimum recruitment levels needed to maintain migratory Osprey populations in the northern hemisphere. However, such high rates may not be needed in the non-migratory population of Australia. Although some early dispersal was recorded among marked Osprey young, strong philopatric recruitment was also evident, with 22% of survivors either remaining on the island, or returning at maturity to join the breeding population. Through the re-identification of individuals, Osprey pairs were found to remain together over many seasons and to use the same primary nesting site. The breeding season began later than reported elsewhere in Australia, extending from August to February, with most laying occurring in September. Undetected nest predation and human disturbance was suspected at accessible nests as contributing to the high level of nest failures recorded. The apparent elongated nestling development period found is comparable to that determined in other studies where fluctuating prey availability directly influenced nestling growth and survival. These factors, plus geographical isolation, suggest the Osprey may be precariously balanced ecologically at the southern extent of its breeding range in Australia.

Osprey Distribution, Abundance, Reproductive Success and Contaminant Burdens Along Lower Columbia River, 1997/1998 Versus 2004

The osprey (Pandion haliaetus) population nesting along the lower portion of the Columbia River (river mile 29 to 286) increased from 94 in 1997 to 103 occupied nests in 1998 (9.6% annual rate of increase) to 225 occupied nests in 2004 (13.9% annual rate of increase). The more recent rate of population increase was associated with higher reproductive rates than in 1997/1998, and significantly lower egg concentrations of most organochlorine (OC) pesticides, polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). A comparison of observed egg residue concentrations in 2004 with effect-level information for ospreys indicated that reproduction at few, if any, nests was adversely affected. As recent as 1997/1998, dichlorodiphenyldichloroethylene (DDE) was still adversely affecting reproductive success for a portion of this population. Mercury was the only contaminant evaluated in both 1997/1998 and 2004 that showed a significant increase in eggs over time, but concentrations in 2004 (0.09 microg g(-1) ww) remained below established effect levels for birds (generally reported at 0.50 microg g(-1) ww or higher). The significant increase in mercury justifies the need for future monitoring. All contaminants mentioned that biomagnify up food chains can be effectively monitored in osprey eggs. The osprey has been shown to be an excellent sentinel species for long-term monitoring with their many useful traits described.

Hunting patterns and success of an osprey (Pandion haliaetus) population at Magdalena Bay, Baja California Sur, Mexico

In late autumn 2004 we studied the effect of water surface condition, wind speed, and tidal status on the hunting patterns (flapping, gliding, hovering) and hunting success of the osprey population at Magdalena Bay, Baja California Sur, Mexico. Through focal sightings we obtained the number of hunting dives, hunting length, and the proportion of hunting length invested in each pattern. Hunting success was 61%. Ospreys required an average of 2.4 dives to catch a prey. Hunting lasted 450 seconds on average, with about 50% of this time invested in flapping, 41% in gliding, and 7% in hovering. The average number of dives to catch a prey varied according to the different water surface conditions, wind speed, and tidal status. The probability of catching a prey decreased when wind speed increased and the condition of the water surface deteriorated; however, hunting length was similar in both cases. Ospreys at Magdalena Bay decrease the proportion of flapping and increase gliding when wind speed increases and the condition of the water surface changes from calm to choppy. The change from low to high tide favored an increase in the probability of catching a prey and in the number of dives, but hunting length was not affected. We compared our results with studies from other regions.

Archaeozoological records and distribution history of the osprey (Pandion haliaetus) in Central Europe

A review of the Holocene records of the osprey (Pandion haliaetus) in Central Europe indicates an immigration around 10,000 years BP at the latest. During the middle Holocene—9,000–5,000 years BP—the species seems to have been common in the south-western Baltic region and perhaps also in Switzerland, but scarce in the rest of Central Europe. After a complete lack of osprey remains for nearly 4,000 years up to medieval times, a few records again suggest a sporadic distribution of this species in the south-western Baltic. In early modern times, the osprey recolonised north-eastern Germany and, during the nineteenth and the first decades of the twentieth century, bred in colony-like densities. Because of relentless persecution and, later, contamination with pesticides, osprey populations collapsed. Recently, the Central European populations have been slowly increasing again. The significance of the subfossil findings is discussed and possible reasons for their scarcity are outlined.

Dacthal and chlorophenoxy herbicides and chlorothalonil fungicide in eggs of osprey ( Pandion haliaetus) from the Duwamish–Lake Washington–Puget Sound area of Washington state, USA

Current-use chlorophenoxy herbicides including 2,4-dichlorophenoxyacetic acid, dicamba, triclopyr, dicamba, dimethyl tetrachloroterephthalate (DCPA or dacthal), and the metabolite of pyrethroids, 3-phenoxybenzoic acid (3-PBA), and the fungicide, chlorothalonil, were investigated in the eggs of osprey ( Pandion haliaetus) that were collected from 15 sites from five study areas Puget Sound/Seattle area of Washington State, USA. DCPA differs from acidic chlorophenoxy herbicides, and is not readily hydrolyzed to free acid or acid metabolites, and thus we developed a new method. Of the 12 chlorophenoxy herbicides and chlorothalonil analyzed only DCPA could be quantified at six of these sites (2.0 to 10.3 pg/g fresh weight). However, higher levels (6.9 to 85.5 pg/g fresh weight) of the unexpected DCPA structural isomer, dimethyl tetrachlorophthalate (diMe-TCP) were quantified in eggs from all sites. diMe-TCP concentrations tended to be higher in eggs from the Everett Harbor area. As diMe-TCP is not an industrial product, and not commercially available, the source of diMe-TCP is unclear. Regardless, these findings indicate that DCPA and diMe-TCP can be accumulated in the food chain of fish-eating osprey, and transferred in ovo to eggs, and thus may be of concern to the health of the developing chick and the general reproductive health of this osprey population.

Contaminant exposure and reproductive success of ospreys (Pandion haliaetus) nesting in Chesapeake Bay regions of concern.

The Chesapeake Bay osprey population has more than doubled in size since restrictions were placed on the production and use of DDT and other toxic organochlorine contaminants in the 1970s. Ospreys are now nesting in the most highly polluted portions of the Bay. In 2000 and 2001, contaminant exposure and reproduction were monitored in ospreys nesting in regions of concern, including Baltimore Harbor and the Patapsco River, the Anacostia and middle Potomac rivers, and the Elizabeth River, and a presumed reference site consisting of the South, West, and Rhode rivers. A "sample egg" from each study nest was collected for contaminant analysis, and the fate of eggs remaining in each nest (n = 14-16/site) was monitored at 7- to 10-day intervals from egg incubation through fledging of young. Ospreys fledged young in regions of concern (observed success: 0.88-1.53 fledglings/active nest), although productivity was marginal for sustaining local populations in Baltimore Harbor and the Patapsco River and in the Anacostia and middle Potomac rivers. Concentrations of p,p'-DDE and many other organochlorine pesticides or metabolites, total PCBs, some arylhydrocarbon receptor-active PCB congeners and polybrominated diphenyl ether congeners, and perfluorooctanesulfonate were often greater in sample eggs from regions of concern compared to the reference site. Nonetheless, logistic regression analyses did not provide evidence linking marginal productivity to p,p'-DDE, total PCBs, or arylhydrocarbon receptor-active PCB congener exposure in regions of concern. In view of the moderate concentrations of total PCBs in eggs from the reference site, concerns related to new and emerging toxicants, and the absence of ecotoxicological data for terrestrial vertebrates in many Bay tributaries, a more thorough spatial evaluation of contaminant exposure in ospreys throughout the Chesapeake may be warranted.

Chlorinated hydrocarbon contamination in osprey eggs and nestlings from the Canadian Great Lakes basin, 1991-1995.

Populations of osprey (Pandion haliaetus) in the Great Lakes basin declined dramatically during the 1950s-1970s due largely to adverse effects of persistent chlorinated hydrocarbons, ingested in their fish prey, on eggshell thickness and adult survival. Nevertheless, these contaminants were not measured in osprey tissues during the decades of decline on the Canadian Great Lakes. Between 1991 and 1995, we monitored recovering osprey populations on the Great Lakes, including Georgian Bay and the St. Marys River area on Lake Huron and the St. Lawrence Islands National Park, as well as at two inland sites within the basin. Current OC levels, even from the most contaminated lakes, were typically lower than those associated with reproductive effects. DDE levels in fresh eggs averaged 1.2-2.9 microg/g, well below the 4.2 microg/g level associated with significant eggshell thinning and shell breakage. Nevertheless, a proportion of eggs from all study areas did exceed this level. PCB levels in eggs seldom exceeded 5 microg/g except in one lake of high breeding density in the Kawartha Lakes inland study area, where the mean sum PCB level was 7.1 microg/g and the maximum concentration measured was 26.5 microg/g. On average, mean reproductive output (0.78-2.75 young per occupied nest) of breeding populations in Great Lakes basin study areas exceeded the threshold of 0.8 young thought necessary to maintain stable populations. We concluded that, although eggs and especially nestling plasma, are useful in reflecting local contaminant levels, ospreys are relatively insensitive, at least at the population level, to health effects of current levels of chlorinated hydrocarbons on the Canadian Great Lakes.

STATUS AND PRODUCTIVITY OF OSPREYS ALONG THE EASTERN COAST OF THE GULF OF CALIFORNIA: 1992–1997

From 1992 to 1997, I monitored population size and productivity of Ospreys (Pandion haliaetus) nesting along 80 km of coast on the eastern side of the Gulf of California, Mexico. During the study period, the number of nesting pairs increased by an estimated 5–14%. The percentage of successful pairs varied significantly among years, ranging from 5–50%. In three of the six years, the productivity of breeding pairs exceeded the estimated level necessary to maintain Osprey population size in at least parts of the species' range. However, three of the last four years were characterized by low reproductive success and by a higher proportion of late clutches. In 1997, the most unproductive of the six years, 38 of 40 (95%) nesting pairs failed to produce any fledgling. That same year, however, the observed productivity of 10 pairs on two nearby islands was 15 times higher than on the mainland. In 1994, 1995, and 1996, successful pairs were significantly clumped, indicating that in the study area, nesting success was strongly influenced by local factors. The results of this study warrant further research to identify the source(s) of annual and spatial differences in nesting success.

Communicative Behavior in Breeding Ospreys (Pandion haliaetus): Description and Relationship of Signals to Life History

ABSmAcr.-The Osprey (Pandion haliaetus), although studied extensively, is relatively unknown with respect to its behavior, especially communication. We conducted a two-year study on a resident Osprey population in Corsica, and describe the communicative behavior of this species. The behavioral repertoire of Ospreys included 11 visual displays (resting, upright, alarm low and high, solicitation low and high, defense, protection, nest protecting, attack, and sky dance) and eight acoustic signals (alarm, solicitation low, high and very high, guard, excited, screaming, and copulation calls). The meaning of each of the displays and calls was inferred from the analysis of behavioral sequences. The communication system of the Osprey consisted of sexual behaviors (between partners), such as solicitation and sky dance, and agonistic behaviors (between breeders and nonbreeders), such as nest-protecting and defense postures. We also analyzed Osprey relationships with other species (including man), and found that there was a gradation within alarm displays and alarm calls according to stimulus distance. In the last section, we try to account for several peculiarities of Osprey behaviors, namely their complexity, the behavioral sexual dimorphism, and the importance of motivational displays. We suggest that all these characters may be related to the life-history traits shown by this species: semicoloniality, breeding strategy, and predation risk (on eggs and chicks). Received 30 March 1992, accepted 25 November 1992.

Lead accumulation and osprey production near a mining site on the coeur d'Alene River, Idaho

Mining and smelting at Kellogg-Smelterville, Idaho, resulted in high concentrations of lead in Coeur d'Alene (CDA) River sediments 15–65 km downstream, where ospreys (Pandion haliaetus) nested. Adult and nestling ospreys living along the CDA River had significantly higher blood lead concentrations than those at Lake Coeur d'Alene (intermediate area) or Pend Oreille and Flathead Lakes (reference areas). Lead concentrations in fish collected from the study areas paralleled those found in ospreys. Inhibition of blood δ-aminolevulinic acid dehydratase (ALAD) activity and elevation of protoporphyrin concentration provided evidence of lead exposure. In adult ospreys, ALAD activity was negatively correlated with lead in blood (r=−0.57), whereas protoporphyrin was positively correlated with lead in blood (r=+0.40). Neither hemoglobin nor hematocrit was adversely affected by the relatively modest lead concentrations found in the blood. Pronounced accumulation of lead by adults or young could ultimately result in behavioral abnormalities or death, both of which would reduce productivity of the nesting osprey population. We did not observe death related to lead, behavioral abnormalities, or reduced productivity during this 1986–87 study. Despite some lead-induced biochemical changes in blood parameters, ospreys produced young at nearly identical rates in the three study areas; these rates were among the highest ever reported in the western United States. Post-fledging survival of ospreys exposed to lead early in life remains an unknown. Lead does not biomagnify in the food chain as do organochlorine pesticides and mercury and several osprey behavior traits reduce the potential for the species to accumulate critical levels of lead. Swans, which feed at a lower trophic level, continue to die from environmental lead in the region.