Egg Loss Research Articles

<b>Effect of protease supplementation on production performance of laying hens

The experiment was conducted with the objective of evaluating the effect of protease enzyme supplementation on performance parameters and quality shell of laying hens. We used 240 Isa Brown commercial laying hens with 44 weeks of age. A completely randomized split-plot design (5 periods of 21 days) with four treatments and six replications (10 hens per replication) was used. The experimental diets were formulated according to the requirements of the breed. The following parameters were evaluated: egg production, feed intake, feed conversion, average egg weight, egg loss, specific gravity, percentage and shell thickness. After collection, the data were analyzed with SISVAR Statistical Package, and the means compared by SNK test at 5% probability. It was concluded that supplementation of diets low in nutrients with 500 g ton -1 of protease (100 U g -1 ), provides egg production and feed conversion rates similar to those obtained in laying hens fed diet with the nutritional level recommended for the breed. However, protease supplementation did not show effect on egg shell quality.

Intense predation of non-colonial, ground-nesting bird eggs by corvid and mammalian predators

Context Loss of eggs to predators is a major cause of reproductive failure among birds. It is especially pronounced among ground-nesting birds because their eggs are accessible to a wide range of predators. Few studies document the main causes of clutch fate of ground-nesting birds. Aims The main objective of the present study was to identify the major egg predator of red-capped plovers (Charadrius ruficapillus). We also investigated the effectiveness of the following two primary strategies available to the plovers to avoid egg predation: (1) the placement of clutches under vegetative cover and (2) avoiding predators by nesting outside the peak season of predator occurrence. Methods Remote-sensing cameras were deployed on plover nests to identify egg predators and nests were monitored over four breeding seasons to document reproductive success and fate. An experiment using false clutches with model eggs investigated the influence of nest cover on the risk of egg predation throughout the year. Line-transect surveys were conducted to estimate the abundance of egg predators in and around the wetlands. Key results The little raven (Corvus mellori) was the major egg predator identified in 78.6% of red-capped plover clutches and in 92.4% of false clutches that were camera-monitored. The hatching success of plover eggs was not influenced by nest cover (P = 0.36), but model egg survival in false clutches improved significantly with the presence of nest cover (P = 0.02). The abundance of little ravens increased during the plover breeding season and was highly negatively correlated with false clutch survival (rpearson = –0.768, P = 0.005). Conclusions Little ravens were the major predator of red-capped plover eggs and their abundance increased significantly during the plover breeding season. Any influence of nest cover on hatching success of eggs may have been masked by the extremely high rate of egg loss associated with the increased little raven abundance during the plover breeding season. Implications The high rate of egg predation is likely to have negative consequences on the local red-capped plover population, suggesting management is warranted. Little raven populations have expanded and, thus, their impact as egg predators needs to be investigated especially on threatened species.

Long-Term Trends in Loggerhead (Caretta caretta) Nesting and Reproductive Success at an Important Western Atlantic Rookery

The Archie Carr National Wildlife Refuge (ACNWR), located along the central east coast of Florida (USA) in the western North Atlantic, hosts one of the largest loggerhead (Caretta caretta) nesting assemblages in the western Hemisphere. Sea turtle nesting activity has been continuously monitored on this beach for > 31 yrs, representing one of the longest sea turtle reproductive data sets in the world. Between 1982 and 2012, an estimated 358,243 nests were deposited on the ACNWR with an estimated annual mean plus 95% confidence interval of 11,556 ± 1,129 nests. This constitutes 25.4% ± 0.8% of the mean annual Florida Index Nesting Beach Survey loggerhead complement. Mean annual clutch size was 113.9 ± 1.4, resulting in a 55.1% ± 4.0% mean annual hatching success rate and a mean emerging success rate of 53.3% ± 3.7%. The only egg-fate that was statistically correlated with emerging success were eggs washed out by erosion. The loss of eggs by erosion was significantly greater during storm and poststorm years, compared with nonstorm years. Among individual first-time nesting females that were measured, mean straight carapace length was 91.2 ± 0.15 cm and mean curved carapace length was 98.2 ± 0.15 cm. These data suggest that the ACNWR supports the greatest loggerhead nest density per kilometer in Florida, underscoring the importance of the ACNWR as one of the most important nesting habitats for loggerhead turtles in the Western Hemisphere.

Habitat limitation and spatial variation in Pacific herring egg survival

Nearshore habitats play a vital role in the life cycles of many marine fishes. These habitats are particularly important for Pacific herring Clupea pallasii, which rely on submerged vegetation in the shallow subtidal for spawning habitat and egg incubation. However, little is known about spatial or temporal variation in egg success or how spawning habitat may affect herring early life history. We estimated herring egg loss rates across multiple spawning vegetations in 5 subpopulations of Pacific herring in Puget Sound (USA), an urbanized estuarine system. We found enormous variation in herring egg loss among subpopulations (range of daily loss rates: 5 to 70%) and in egg loss of eggs reared under common garden conditions (range of cumulative loss: 20 to 100%). Egg loss varied by subpopulation but not by spawning vegetation type. Exploratory analyses suggest both wave height and land use patterns may affect hatch success. Using historical survey data, we found that a large proportion of spawning habitat available to Puget Sound herring remains unused each year. Furthermore, we found limited evidence that eggs were deposited dis- proportionally on particular vegetation types; only the non-indigenous brown algae Sargassum mu- ticum was spawned on more than expected by chance. Our results demonstrate that Puget Sound herring are not limited by the amount of available suitable spawning vegetation, and that native vegetation is not preferred over other vegetation types for herring spawning. Rather, it appears that other terrestrial or marine variables are likely determinants of herring egg loss.

Microclima, idade das matrizes e tempo de estocagem influenciando nas respostas produtivas de ovos férteis

Objetivou-se, com esta pesquisa, avaliar as condições microclimáticas da sala de ovos e sua influência na perda de água dos ovos férteis em função das diferentes idades de matrizes e tempos de estocagem. A sala de ovos apresentava as seguintes dimensões: 15 x 9,90 x 2,8 m, climatizada por quatro aparelhos de ar condicionados. Foram selecionadas três diferentes idades de matrizes e três intervalos de tempo de estocagem. Quando as aves atingiam as três idades eram coletados 1440 ovos, foram coletados a massa (kg) de 140 ovos individualizados de cada tratamento, durante sua entrada e saída da sala utilizando-se uma balança semianalítica para avaliação da perda de água dos ovos. A avaliação microclimática da sala foi realizada em intervalos de 10 min. por meio do registro de temperatura (°C), umidade relativa (%) e entalpia específica (kJ kg-1 de ar seco) utilizando-se 19 dataloggers. O delineamento experimental utilizado foi inteiramente aleatorizado com esquema fatorial 3 x 3. As condições microclimáticas da sala se mantiveram acima da faixa ideal e o verão foi o período mais quente. Os ovos oriundos de matrizes velhas e intermediárias com o tempo de estocagem de 50-52 h apresentaram as maiores perdas de água.

Egg shell ultrastructure of the dragonfly, Micrathyria dictynna Ris (Anisoptera: Libellulidae)

A highly specialized form of egg deposition occurs in the dragonfly Micrathyria dictynna, which attaches egg-masses onto the underside of leaves high above shallow streams in Central American rainforests. Here, we describe the ultrastructure of the egg chorion of M. dictynna to reveal structural adaptations related to this unusual form of oviposition. We find that the egg chorion is generally divided into a thin, sticky exochorion and a tough, hard, smooth endochorion. The exochorion of eggs collected from the peripheral region of egg masses, however, shows a separation into outer and inner exochorionic layers. The space formed between these layers develops numerous pillars. In eggs collected from the area between the periphery and central region of an egg mass, the exochorion exhibits irregular interconnected patches of elevated areas containing very fine superficial linear reticulations. We propose that the exochorion of peripheral eggs is functionally modified to form a plastron that regulates respiration and restricts water loss of eggs in the inner layers of the egg mass.

The effect of eggshell apex abnormalities on table egg quality during storage in 2 seasons of the year

Mycoplasma synoviae infection of hens has been associated with problems of eggshell quality called eggshell apex abnormalities (EAA). Little is known about the quality of EAA eggs from a commercial point of view, especially during their storage. The study aimed to examine the differences between EAA and normal eggs during storage under controlled conditions in 2 seasons, summer and winter, by comparing internal and external quality parameters. In a conventional egg production farm with white laying hens of varying ages in the city of Bastos, state of São Paulo, Brazil, 232 eggs were used in the summer season and 400 eggs in the winter season. Half of the eggs had EAA, and the other half were considered normal eggs for each season. The eggs were analyzed at 2, 7, 14, 21, and 28 d after being laid and stored from 24.6 to 25.8°C in summer and from 24 to 25°C in winter. There was no difference (P > 0.05) in the average egg weight between EAA and normal eggs at any studied time point, but in both seasons, the weight loss in EAA eggs was higher than in normal eggs. The losses in Haugh unit scores from the first to the last measurements were approximately 40% regardless of egg type or season of production. In comparing eggshell thickness, only the apices of the EAA eggs were thinner (P < 0.0001) than normal eggs in the summer, but in the winter, the EAA egg apices (P < 0.0001) and sides (P = 0.03) were both thinner. The presence of EAA did not affect the eggshell weight (P > 0.05) or eggshell percentage (P > 0.05). The eggshell strength of the EAA eggs was lower (P < 0.0001) than normal eggs in both the summer (16.57%) and winter (19.86%). The presence of EAA did not affect the internal quality of the egg, but was related to a greater loss of external quality and weight during storage.

Egg loss in females of two lithodid species following different return-to-the-water protocols

Coastal waters of the southern tip of South America have sustained a mixed king crab fishery since the 1930s, with two target species: the southern king crab Lithodes santolla and the stone crab Paralomis granulosa. The fisheries are managed with the so-called 3S rule (Sex, Season, and Size) and females must be returned to the water. In king crabs, fecundity can be reduced by several mechanisms, but those related to fishing activities are only partially known. In this article, we tested experimentally whether egg loss is caused by the return of L. santolla and P. granulosa ovigerous females to the water. To do so, we performed experiments for each species with a 3×2 different return-to-the-water conditions: free fall, ramp, or a no-fall (control), with or without previous aerial exposure of females. Our experiments demonstrate that free fall impacts, similar to the normal practice in the fishery of the Beagle Channel, result in egg loss in both the species. Female L. santolla lost more eggs if females were exposed to air prior to the dropping. Also, eggs with more developed embryos were likely to be lost as a result of tumbling. In both the species, the use of a ramp for the returning of crabs to water caused an egg loss similar to those of the experimental controls. In P. granulosa fecundity from three areas with different fishing effort suggest that the return of females to the water may be a negative effect that could be detected at a population level. To our knowledge, this is the first study that demonstrates the egg loss of female crabs returned to the water in a fishery.

Multiple Lines of Egg Defense in a Neotropical Arachnid with Temporary Brood Desertion

AbstractEgg predation is the one of the main costs of brood desertion in many ectothermic animals. When stressful environmental conditions constrain parental activities to only some periods of the day, the combination of physical or chemical defenses may attenuate the costs related to egg loss during periods of temporary parental absence. Females of the harvestman Neosadocus maximus periodically abandon their clutches to shelter or forage. They also cover their eggs with a hygroscopic mucus coat and seem to lose fewer eggs to predation than other syntopic harvestmen whose eggs lack the mucus coat. Using two species of N. maximus egg predators, we demonstrate that eggs whose mucus coat was experimentally removed suffered higher predation rate than eggs whose mucus coat was left intact. We argue that this mucus provides physical protection against egg predators, especially small arthropods. A similar mucus coat has independently evolved in other two clades of Neotropical harvestman in which males care for the eggs and typically leave their clutches unattended for several hours a day. We propose that the presence of multiple lines of egg defense may have evolved as a way of lowering the costs imposed by intra‐ and interspecific egg predation during periods of temporary brood desertion.

Reproductive parameters in the critically endangered Blue-throated Macaw: limits to the recovery of a parrot under intensive management.

Rediscovered in the wild twenty years ago, the breeding biology of wild Blue-throated Macaws remains largely unexplored, yet is essential to its effective conservation and recovery. Here, we analyse reproductive parameters in an intensively managed wild population of Blue-throated Macaws, providing the first data on the breeding biology of this critically endangered species. During the six-year study period, 2007–2012, the number of active breeding pairs either remained constant or decreased, depending on the site, and no new breeding pairs were discovered despite extensive searching. We documented nesting attempts in natural cavities in dead palms or live hardwoods, and artificial nest boxes. Egg-laying was concentrated during the end of dry season and the beginning of the wet season, August through December. Hatching failure was the greatest cause of egg losses. Half of the breeding attempts of Blue-throated Macaws produced at least one fledging, on average two, after a 85 days nestling period. An average of 4.3 nestlings per year fledged from all known wild nests combined. Each pair lost roughly 65% of its initial reproductive investment at each nesting attempt. In most successful nesting attempts of individualized pairs, a new nesting attempt was not detected the following year. All monitored breeding pairs showed high nest site fidelity, reusing hardwood-tree cavities and nest boxes. Our findings will aid conservation efforts by refining current actions and prompting new approaches towards the conservation and recovery of the Blue-throated Macaw.

Longer ice-free seasons increase the risk of nest depredation by polar bears for colonial breeding birds in the Canadian Arctic

Northern polar regions have warmed more than other parts of the globe potentially amplifying the effects of climate change on biological communities. Ice-free seasons are becoming longer in many areas, which has reduced the time available to polar bears (Ursus maritimus) to hunt for seals and hampered bears’ ability to meet their energetic demands. In this study, we examined polar bears’ use of an ancillary prey resource, eggs of colonial nesting birds, in relation to diminishing sea ice coverage in a low latitude region of the Canadian Arctic. Long-term monitoring reveals that bear incursions onto common eider (Somateria mollissima) and thick-billed murre (Uria lomvia) nesting colonies have increased greater than sevenfold since the 1980s and that there is an inverse correlation between ice season length and bear presence. In surveys encompassing more than 1000 km of coastline during years of record low ice coverage (2010–2012), we encountered bears or bear sign on 34% of eider colonies and estimated greater egg loss as a consequence of depredation by bears than by more customary nest predators, such as foxes and gulls. Our findings demonstrate how changes in abiotic conditions caused by climate change have altered predator–prey dynamics and are leading to cascading ecological impacts in Arctic ecosystems.

Relationships of incubational hatching egg characteristics to posthatch body weight and processing yield in Ross × Ross 708 broilers ,

The characteristics of broiler hatching eggs have the potential to effect broiler posthatch growth and processing yield. The association of set egg weight (SEW), length of incubation (LI), and mean daily percentage of incubational weight loss (MDPEWL) of embryonated Ross × Ross 708 broiler hatching eggs with subsequent posthatch BW and processing yield was investigated. Sixty Ross × Ross 708 broiler hatching eggs were randomly set on each of 8 replicate tray levels of an incubator. Weight loss of individual embryonated eggs between 0 and 10.5, 10.5 and 18.5, and 0 and 18.5 d of incubation was determined for the calculation of MDPEWL. Furthermore, on 18.5 d of incubation, embryonated eggs were transferred to a hatcher unit where they were individually monitored for hatch every 12 h for determination of LI. Chicks were placed in corresponding replicate floor pens and were grown out from 0 (21.5 d of incubation) to 49 d posthatch. Live bird BW as a percentage of SEW on 21.0 d of incubation and d 0 and 49 posthatch, and bird sex on d 49 posthatch were determined. After commercial processing, carcass weight as a percentage of SEW, and carcass, abdominal fat pad, wings, breast muscle, tenders, drumsticks, and thighs weights as percentages of live BW were determined. Bird BW on 21.0 d of incubation and on d 0 and 49 posthatch were positively correlated or interrelated with SEW. Between 0 and 10.5 d of incubation, MDPEWL was negatively correlated with absolute and relative BW on 21.0 d of incubation, absolute BW on d 0 posthatch, and relative tenders weight. Further, LI was positively correlated with absolute and relative BW on 21.0 d of incubation and d 0 posthatch, but was negatively correlated with relative (percentage of live BW) carcass weight on d 49 posthatch. The MDPEWL of modern strain broiler hatching eggs should be closely monitored, particularly during the first half of incubation, for the regulation of LI and hatchling BW and for their potential effects on processing yield characteristics.

Relationship between lake trout spawning, embryonic survival, and currents: A case of bet hedging in the face of environmental stochasticity?

Lake trout, Salvelinus namaycush, spawning in the Great Lakes occurs primarily on cobble substrate at relatively shallow water depths that can experience strong water currents. Strong currents may limit embryonic survival by damaging or displacing eggs, but may also reduce the accumulation of fine material and limit foraging by potential egg predators. To better understand the importance of currents, we evaluated the role of currents in spawning habitat selection, egg density and survival, and egg predator density at a spawning reef in Lake Champlain (USA). Most spawning occurred one week after the largest storm event associated with the strongest currents and greatest upwelling. Highest spawning activity was associated with a relatively shallow part of the reef that had the highest current velocity and greatest potential for egg displacement. Within the interstices, the survival of naturally deposited eggs was unrelated to the concurrent loss of artificial eggs. We propose that the reproductive strategy of spawning on shallow areas of a reef that have the highest current velocity and high potential for egg loss represents a type of bet hedging to optimize survival of those embryos that remain within interstices. This strategy may have evolved in response to environmental stochasticity that resulted in higher egg survival.

Fecundity of the langoustine Metanephrops mozambicus Macpherson, 1990 (Decapoda, Nephropidae) in eastern South Africa

The fecundity of the langoustineMetanephrops mozambicusMacpherson, 1990 was investigated using egg-bearing females caught in commercial trawls off eastern South Africa. A generalized linear model (GLM) framework was used to assess fecundity and egg diameter relative to langoustine carapace length (CL) and egg developmental stage. Fecundity ranged from 407 to 1606 eggs per clutch, increased with increasing CL and decreased between egg stages 1 and 4. Egg diameter increased significantly between stages 1 and 4 and larger females carried larger eggs. Egg loss during incubation was estimated at 10%. Four egg stages used during field sampling were re-examined and illustrated. A late stage embryo removed from an egg about to hatch appeared to be adapted to a benthic, rather than natatory existence.

Productive performance, eggshell quality, and eggshell ultrastructure of laying hens fed diets supplemented with organic trace minerals

This study was carried out with the purpose of evaluating the effect of supplementing hens' diets with trace minerals from inorganic or organic sources on the productive performance, eggshell quality, and eggshell ultrastructure of laying hens. Three hundred sixty Hy-Line W36 laying hens between 47 to 62 wk of age were used and distributed in a completely randomized experimental design with 9 treatments, 5 replicates, and 8 birds for each experimental unit. The treatments consisted of a control diet without supplementation of the trace minerals Mn, Zn, and Cu; 4 supplementation levels of these trace minerals from an inorganic source; and the same levels of supplementation from an organic source (proteinates). The supplementation levels in milligrams per kilogram for Mn, Zn, and Cu, were, respectively, 35-30-05, 65-60-10, 95-90-15, and 125-120-20. There was no effect of supplementation of trace minerals on the rate of posture, feed intake, feed conversion, specific weight, and Haugh unit of eggs. However, there was a quadratic effect (P < 0.05) of the levels of trace mineral supplementation on average egg weight and egg mass; the results did not differ regarding the source used. The increase in the levels of supplementation of Mn, Zn, and Cu provided a linear increase (P < 0.05) in the breaking strength and the percentage of eggshell. There was a linear decrease (P < 0.05) in the egg loss and the number of mammillary buttons in the shell. The best results were obtained using diets supplemented with trace minerals from an organic source because these diets provided lower egg loss, higher thickness, and increased strength of the shell. Structurally, organic Mn, Zn, and Cu provided higher thickness of the palisade layer and lower mammillary density. The trace mineral supplementation improved the structural characteristics and the quality of the eggshells.

Comparing effects of α‐ vs. β‐chitosan coating and emulsion coatings on egg quality during room temperature storage

SummaryEffects of α‐ and β‐chitosan (CH), soybean oil (SO) and their emulsions (CH:SO = 2:3) as coating materials on selected internal quality and sensory properties of eggs were evaluated during 5 weeks storage at 25 °C. After 3 weeks of storage, α‐ and β‐CH‐coated eggs changed to B grade, while SO‐ and emulsion‐coated eggs preserved grade A quality. Weight loss of eggs coated with SO and CH:SO emulsions was &lt;2.0% vs. 5.3–5.8% for noncoated and CH‐coated eggs after 5 weeks of storage. β‐CH (0.9%) maintained lower weight loss of eggs than α‐CH (1.2%) only at 1‐week storage. Albumen pH of eggs coated with SO and CH:SO emulsions decreased progressively throughout storage. Eggs coated with β‐CH:SO emulsion and SO were significantly glossier than noncoated eggs. Consumers indicated positive purchase intent (69.17–76.67%) for all coated eggs. Overall, α‐CH:SO and β‐CH:SO emulsions extended egg shelf life by at least 3 weeks during room temperature storage.

A closed recirculating aquaculture system for artificial seed production of the European eel (Anguilla anguilla): Technology development for spontaneous spawning and eggs incubation

The objective of the present study was to obtain spontaneous reproduction in captivity of the European eel (Anguilla anguilla) by using a new closed recirculating aquaculture system provided with spawning and incubation chambers. The influence of two levels of water-flow rates (Low-Flow: 0.8±0.05L/s and High-Flow: 2.4±0.05L/s) on the spawning, fecundity and egg quality was also investigated. For this purpose 12 silver eel females were induced with increasing doses of carp pituitary extract (10, 20, 30 and 40mg CPE/kg BW). Twenty-four hours after the last CPE injection, each female ovulation was induced by injecting a DHP-solution and then transferring them to a new closed recirculating aquaculture system, where they were maintained for 16h with spermiating males (sex ratio 4/1) in order to obtain spontaneous reproduction. The reproduction was tested with 6 females in Low-Flow rate conditions and 6 females in High-Flow rate conditions.The results showed that the designed closed-loop system made it possible to carry out a more spontaneous reproduction for more than 80% of the females that underwent standardized gonadotropic treatment and favored the automatic and complete transfer of the eggs to the hatchery. The results also point out that high or low water current conditions in the tank do not hinder the mating and the emission of gametes by the breeders, but the High-Flow rate in the two incubation chambers showed unsuitable hydrodynamic conditions for embryonic development resulting in a constant loss of viable eggs which reached a mortality of 100% among females with the highest incubation density.

Impact of fowlpox-vectored Mycoplasma gallisepticum vaccine Vectormune FP MG on layer hen egg production and egg quality parameters

This study was conducted to determine the impact of vaccination with Vectormune FP MG on egg production and egg quality characteristics of Single Comb White Leghorn hens. Due to questions of the efficacy of this vaccine in preventing Mycoplasma gallisepticum-mediated pathology, the ability of this vaccine to protect against postproduction-peak egg losses associated with F-strain M. gallisepticum (FMG) vaccination was also investigated. Vaccination with Vectormune FP MG did not result in any significant change in egg production or egg quality parameters compared with control (unvaccinated) hens. Subsequent revaccination with FMG at 45 wk of age (woa) yielded no impact on egg production or egg quality parameters of Vectormune FP MG vaccinated hens, unlike prior results for postproduction-peak vaccination of M. gallisepticum-clean hens with FMG, which exhibited a drop in egg production of approximately 6%. No difference in egg size distribution was observed for any of the treatment groups before or after FMG revaccination. These results suggest that hens can be safely vaccinated with Vectormune FP MG as pullets and can be revaccinated with a live M. gallisepticum vaccine such as FMG at a later date with no deleterious effects on egg production or egg or eggshell quality parameters.

Chick and juvenile survival of Japanese rock ptarmigan Lagopus muta japonica

We estimated clutch size, hatching success, chick survival before independence from hens and juvenile survival after independence in Japanese rock ptarmigan Lagopus muta japonica during 2006‐2012 on Mt. Norikura, Honshu, Japan. The tame behaviour of this subspecies provided us a unique opportunity to observe them at a close range throughout the period from hatching to adulthood. The average clutch size was 5.7 ± 0.1 (± SE). We estimated the average hatching success to be 0.602 ± 0.880, the average nest hatching success to be 0.733 ± 1.071, the average hatchability of successful nests to be 0.907 ± 0.017 and average female survival during June, as an indicator of their survival during laying and the incubation periods, to be 0.905 ± 0.055. We attributed all egg losses to predation by carnivores. Clutch size, nest success, hatchability and female survival during June did not vary among years. Chick survival decreased sharply during the first four weeks of the brooding season. The average annual chick survival until independence was 0.278 ± 0.097, but it varied from 0.096 ± 0.051 to 0.639 ± 0.084. Survival of juveniles after independence was higher than for chicks before independence. Average over‐winter survival of juveniles was larger and was 0.902 ± 0.015. We estimated the average reproductive success of Japanese rock ptarmigan from egg‐laying to one year old to be 0.586 ± 0.883 birds/breeding female. Weather conditions, especially rainfall, during the first two weeks of the brooding season appeared to negatively affect chick survival.

Eggshell thinning of osprey (Pandion haliaetus) breeding in Sweden and its significance for egg breakage and breeding outcome

In the middle of the 1960s low reproductive rate was found in several osprey (Pandion haliaetus) nests in Sweden. Therefore a project was started to investigate the production and to collect unhatched eggs and shell fragments in different regions of Sweden during 1971–2008. Measurements of osprey eggs from museum collections from 1840 to 1970 were included to study long-term changes in shell thickness. In total, eggshell thickness of whole eggs from 666 clutches and of shell fragments from 693 nests was measured.The thinnest shell fragments were recorded in 1973 (mean for 71 clutches: 0.438mm), minus 15.0% compared to thickness of unaffected eggs before 1946 (0.515mm). After 1973, shell thickness increased to reach background levels in 2003 (0.515mm). Thus, it took 30years to reach full thickness again. From the start of the decrease it took more than 50years to reach unaffected conditions. The number of whole eggs remaining intact in the nest throughout incubation was reduced when shell thickness decreased. Great loss of eggs due to breakage seems to occur when the mean shell thickness in the clutch was below 0.40mm. In 1971–1973, when shell thinning was most pronounced, the average thickness of shell fragments was 0.366mm in nests with 0 intact eggs (minus 29% compared to the pre-1946 background value); 0.393mm (minus 24%) in nests with 1 intact egg; 0.431mm (minus 16%) in nests with 2 intact eggs and 0.450mm (minus 12%) in nests with 3 intact eggs. Differences in thickness were significant for 1 versus 2 intact eggs, 2 vs. 3 intact eggs and for 0+1 vs. 2+3 intact eggs. Actual data from the period 1971–73 shows a decline in the production of young (4–5weeks) of some 15% (0.25 young per nest).