Suchergebnisse

In two seasons following lower than average annual rainfall, silver gulls laid smaller clutches, their
eggs were smaller and the sequential decrease in egg volume within a clutch was more pronounced
than in a year preceded by heavier rainfall.

An isolated population of malleefowl (Leipoa ocellata) at Yalgogrin in New South Wales, Australia, was studied intensively between 1986–87 and 1998–99. During this period the population produced 124 clutches, comprising a total of 1705 eggs. The number of clutches per annum varied between 5 and 15. Eggs were laid between mid-August and mid-February, with 90% laid between the last week of September and the first week of January. The mean date of laying of the first egg of each clutch (±s.d.) was 21 September ± 13 days and the mean date of the last egg was 23 December ± 19 days. The mean duration of egg laying varied significantly between years (range 70–117 days) and was negatively correlated with the daily maximum ambient temperature in December. Cool temperatures and rain in early summer prolonged the laying season. The mean interval between laying was 6.4 ± 1.1 days (range 3–12 days), with eggs laid at a faster rate during the first half of the laying period. Overall, mean clutch size was 14.1 ± 5.8 (range 1–28). Large clutches were the result of an extended period of laying rather than an increase in the rate of laying. Mean clutch size was greatest when laying extended into mid-February. The best predictor of clutch size was rainfall between May and December – the interval spanning both nest construction and egg laying. The mean volume of all measured eggs (n = 1362) was 162.1 ± 9.0 mL (range 99–200 mL). Egg volume varied during the laying period, with those eggs laid early or late in the breeding season being smaller. Eggs at Yalgogrin were, on average, 10.5% smaller than those recorded at nearby Pulletop.

Brood-parasitic cuckoos lay their eggs in the nests of other birds and thereafter abandon their young to the care of the host. Thus, all maternal investment is restricted to investment in the egg. Optimal investment at this stage is likely to have a large impact on maternal reproductive success. Many bird species optimize the size of their eggs to suit both the prevailing environmental conditions and the number of individuals that will provide care to the chicks. However, relatively few cues are available to avian brood parasites to facilitate optimal investment in their eggs. Moreover, optimization of egg size to suit environmental conditions or the social structure of the host group may be constrained by stronger selection for egg mimicry, which reduces the likelihood of detection and rejection of foreign eggs by the host. We aimed to test how the conflicting selection pressures of (1) selection for large eggs in harsh environmental conditions versus (2) rejection of large eggs by hosts interact to influence the size and shape of Horsfield's bronze-cuckoo, Chalcites basalis, eggs. Using a sliding window approach to investigate periods of climate sensitivity, we show that climatic variables did not predict egg size. Nor did cuckoos modify their egg size or shape in relation to the group size of the host (superb fairy-wren, Malurus cyaneus). Conversely, host defences did appear to have influenced cuckoo egg morphology: eggs that were relatively short and round had a higher probability of being abandoned by the host than eggs that were long and narrow. This suggests that host defences are the overriding selection pressure on cuckoo egg morphology, and, unlike their hosts, cuckoos do not adapt their eggs to the prevailing climate or host group size. ; This work was supported by an Australian Research Council grant (DP180100021) to N.E.L. and an Australian Government Research training Program scholarship to C.J.T. We declare there are no conflicts of interest.

Seabirds nesting on islands are threatened by invasive rodents, such as mice and rats, which may attack eggs, chicks and even adults. The low feasibility of rat eradications on many islands makes the development of alternate control plans necessary. We used a combination of field experiments on a Mediterranean island invaded by black rats (Rattus rattus) to evaluate (1) the predation risk posed to different-sized seabird eggs and (2), the potential of two deterrent methods (electronic and chemical) to reduce its impact. Rats were able to consume eggs of all sizes (12 to 68 g), but survival increased 13 times from the smallest to the largest eggs (which also had more resistant eggshells). Extrapolation to seabird eggs suggests that the smallest species (Hydrobates pelagicus) suffer the most severe predation risk, but even the largest (Larus michahellis) could suffer >60% mortality. Nest attack was not reduced by the deterrents. However, chemical deterrence (conditioned taste aversion by lithium chloride) slowed the increase in predation rate over time, which resulted in a three-fold increase in egg survival to predation as compared to both control and electronic deterrence. At the end of the experimental period, this effect was confirmed by a treatment swap, which showed that conferred protection remains at least 15 days after cessation of the treatment. Results indicate that small seabird species are likely to suffer severe rates of nest predation by rats and that conditioned taste aversion, but not electronic repellents, may represent a suitable method to protect colonies when eradication or control is not feasible or cost-effective. © 2013 Latorre et al. ; Funds were provided by the Environment and Nature Council of the Balearic Government (project DRAGORAT; Sa Dragonera Natural Park's research grants, IX Edition, 2007). ARL received funding support from the Spanish Scientific Research Council (JAEDoc program, co-funded by the European Social Fund). The Spanish Ministry of Science and Innovation also supported this work by the awarded project SEAGRAPE, ref. CGL2011-30249 ; Peer Reviewed

Statistics are given for egg dimensions, clutch size, laying rate and incubation period in black swans nesting at Lake George and Lake Bathurst, N.S.W., and compared with data from other studies.

Methods of determining clutch size and incubation dates are given and examined. Emphasis is placed on the importance of the method of assessment of clutch size in comparisons within and between studies.

There was evidence of two size classes of eggs, possibly related to factors of age or breeding experience, the smaller class being laid in summer breeding, during an exceptional abundance of food, but not in winter when food may have been limiting. Egg size varied significantly, according to sequence in the clutch. The adaptive significance of egg size is discussed; moisture loss may be
important in the evolution of egg size.

Clutch size varied significantly according to the location and date of nesting. The reasons for the variation were, possibly, both in the nutritional value of the food available and in its relative temporal and physical availability and the swans' abllity to metabolize it. Possible evolutionary determinants of average clutch size in the black swan are considered. Moisture losses from the egg may again he important.

The laying rate was simdar to that reported elsewhere. The mean incubation period was 40.45 days and most clutches ranged from 39 to 43 days.

Clutches laid in autumn and winter took marginally longer to hatch than clutches laid in spring and summer, possibly due to effects of ambient temperature; the difference was probably not of particular adaptive significance.

Brood parasitism frequently leads to a total loss of host fitness, which selects for the evolution of defensive traits in host species. Experimental studies have demonstrated that recognition and rejection of the parasite egg is the most common and efficient defence used by host species. Egg-recognition experiments have advanced our knowledge of the evolutionary and coevolutionary implications of egg recognition and rejection. However, our understanding of the proximate mechanisms underlying both processes remains poor. Egg rejection is a complex behavioural process consisting of three stages: egg recognition, the decision whether or not to reject the putative parasitic egg and the act of ejection itself. We have used the blackbird (Turdus merula) as a model species to explore the relationship between egg recognition and the act of egg ejection. We have manipulated the two main characteristics of parasitic eggs affecting egg ejection in this grasp-ejector species: the degree of colour mimicry (mimetic and non-mimetic, which mainly affects the egg-recognition stage of the egg-rejection process) and egg size (small, medium and large, which affects the decision to eject), while maintaining a control group of non-parasitized nests. The behaviour of the female when confronted with an experimental egg was filmed using a video camera. Our results show that egg touching is an indication of egg recognition and demonstrate that blackbirds recognized (i.e., touched) non-mimetic experimental eggs significantly more than mimetic eggs. However, twenty per cent of the experimental eggs were touched but not subsequently ejected, which confirms that egg recognition does not necessarily mean egg ejection and that accepting parasitic eggs, at least sometimes, is the consequence of acceptance decisions. Regarding proximate mechanisms, our results show that the delay in egg ejection is not only due to recognition problems as usually suggested, given that experimental eggs are not touched significantly more often. Thus, the delay in egg ejection is mainly the consequence of a delay in the decision to eject, probably triggered by mechanical constraints imposed by eggs that are harder to eject (i.e. larger). Our results offer important information on the relationships between recognition and ejection and contribute to a better understanding of host defences against brood parasites. ; Financial support was provided by the Junta de Andalucía (research project CVI-6653). JDI is funded by a postdoctoral contract (TAHUB-104) from the "Andalucía Talent Hub" program (co-funded by the European's Union Seventh Framework Program Marie Skłodowska-Curie actions (COFUND) and the regional Government of Andalucía).

Solar radiation is an important driver of animal coloration, not only because of the effects of coloration on body temperature but also because coloration may protect from the deleterious effects of UV radiation. Indeed, dark coloration may protect from UV, but may increase the risk of overheating. In addition, the effect of coloration on thermoregulation should change with egg size, as smaller eggs have higher surface‐volume ratios and greater convective coefficients than larger eggs, so that small eggs can dissipate heat quickly. We tested whether the reflectance of eggshells, egg spottiness, and egg size of the ground‐nesting Kentish plover Charadrius alexandrinus is affected by maximum ambient temperature and solar radiation at breeding sites. We measured reflectance, both in the UV and human visible spectrum, spottiness, and egg size in photographs from a museum collection of plover eggshells. Eggshells of lower reflectance (darker) were found at higher latitudes. However, in southern localities where solar radiation is very high, eggshells are also of dark coloration. Eggshell coloration had no significant relationship with ambient temperature. Spotiness was site‐specific. Small eggs tended to be light‐colored. Thermal constraints may drive the observed spatial variation in eggshell coloration, which may be lighter in lower latitudes to diminish the risk of overheating as a result of higher levels of solar radiation. However, in southern localities with very high levels of UV radiation, eggshells are of dark coloration likely to protect embryos from more intense UV radiation. Egg size exhibited variation in relation to coloration, likely through the effect of surface area‐to‐volume ratios on overheating and cooling rates of eggs. Therefore, differential effects of solar radiation on functions of coloration and size of eggshells may shape latitudinal variations in egg appearance in the Kentish plover. ; Ministerio de Economía y Competitividad of Spain SEV‐2012‐0262 ; Spanish Government CGL2011‐24230 CGL2017‐83518‐P ; Ministerio de Educación, Cultura y Deporte, Spain FPU12‐01616 ; Biotechnology and Biological Sciences Research Council (BBSRC) BB/J018309/1

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record. ; Solar radiation is an important driver of animal coloration, not only because of the effects of coloration on body temperature but also because coloration may protect from the deleterious effects of UV radiation. Indeed, dark coloration may protect from UV, but may increase the risk of overheating. In addition, the effect of coloration on thermoregulation should change with egg size, as smaller eggs have higher surface-volume ratios and greater convective coefficients than larger eggs, so that small eggs can dissipate heat quickly. We tested whether the reflectance of eggshells, egg spottiness and egg size of the ground-nesting Kentish plover Charadrius alexandrinus are affected by maximum ambient temperature and solar radiation at breeding sites. We measured reflectance, both in the UV and human visible spectrum, spottiness and egg size in photographs from a museum collection of plover eggshells. Eggshells of lower reflectance (darker) were found at higher latitudes. However, in southern localities where solar radiation is very high, eggshells are also of dark coloration. Eggshell coloration had no significant relationship with ambient temperature. Spotiness was site-specific. Small eggs tended to be light-coloured. Thermal constraints may drive the observed spatial variation in eggshell coloration, which may be lighter in lower latitudes to diminish the risk of overheating as a result of higher levels of solar radiation. However, in southern localities with very high levels of UV radiation, eggshells are of dark coloration likely to protect embryos from more intense UV radiation. Egg size exhibited variation in relation to coloration, likely through the effect of surface area-to-volume ratios on overheating and cooling rates of eggs. Therefore, differential effects of solar radiation on functions of coloration and size of eggshells may shape latitudinal variations in egg appearance in the Kentish plover. ; Financial support was received from Estación Biológica de Doñana (EBD-CSIC) through Severo Ochoa Programme for Centres of Excellence (grant SEV-2012-0262, Ministerio de Economía y Competitividad of Spain), and partly by grants CGL2011-24230 and CGL2017-83518-P from the Spanish Government, with EU-ERDF financial support. JG was supported by an FPU predoctoral fellowship (FPU12-01616) from Ministerio de Educación, Cultura y Deporte, Spain. MS and JT were funded by a Biotechnology and Biological Sciences Research Council (BBSRC) grant BB/J018309/1 to MS.

Latitudinal and temperature-related clines in egg size were found for the peregrine falcon, Falco
peregrinus, in Australia, egg size increasing with increasing latitude and decreasing temperature. The
breakdown of these clines since the 1940s corresponded temporally with the introduction of DDT to
agriculture and with greater intensification of land use. In eggs collected since the 1940s, the clines were
still present north of 33�S. and in areas where the mean maximum September temperature was e21�C,
but not south of 34�S. and in areas of mean maximum September temperature < 21�C. Mean clutch size
was 2.9 (range 1-5); without evidence of clines. Most eggs were collected in September in south-eastern
Australia. The timing of the egg-laying period was correlated with latitude and temperature,
corresponding to the seasonal influx of migrant prey species and the breeding season of major prey
species. The geographical distribution of cliff nests, stick nests and tree-hollow nests is discussed; the use
of hollow trees appears to be restricted geographically. Eggs from some tree-hollow nests were larger than
those from other types of nest.

The aim of the present paper was to analyze the measurements of the Eurasian Coot (Fulica atra) eggs in order to evaluate if the local conditions, presented here, differ in some way from older data found in references dating to 1955 in Romania. The data were collected from the Eurasian Coot nests identified (N=8) at Câmpenești fishponds, located in North-Western Romania, in May 2018. The clutch size was 7.5 ±1.6, ranging from 5 to 10 eggs. The mean egg length was 50.81 mm, and the mean egg breadth was 34.5 mm with higher variability in case of the first measurement. The mean egg volume was 31.3 cm3 which is much smaller than reported in the Romanian references (36.13 cm3). Regarding intra-clutch variance, we found that some clutches manifest a higher length, breadth and volume variance than others which can be a result of the intraspecific nest parasitism or environmental variances. The results brought some extensions of egg length and egg breadth limits and also may reflect a decrease in egg size over time.

Design of surveillance programs to detect infections could benefit from more insight into sampling schemes. We address the effect of sampling schemes for Salmonella Enteritidis surveillance in laying hens. Based on experimental estimates for the transmission rate in flocks, and the characteristics of an egg immunological test, we have simulated outbreaks with various sampling schemes, and with the current boot swab program with a 15‐week sampling interval. Declaring a flock infected based on a single positive egg was not possible because test specificity was too low. Thus, a threshold number of positive eggs was defined to declare a flock infected, and, for small sample sizes, eggs from previous samplings had to be included in a cumulative sample to guarantee a minimum flock level specificity. Effectiveness of surveillance was measured by the proportion of outbreaks detected, and by the number of contaminated table eggs brought on the market. The boot swab program detected 90% of the outbreaks, with 75% fewer contaminated eggs compared to no surveillance, whereas the baseline egg program (30 eggs each 15 weeks) detected 86%, with 73% fewer contaminated eggs. We conclude that a larger sample size results in more detected outbreaks, whereas a smaller sampling interval decreases the number of contaminated eggs. Decreasing sample size and interval simultaneously reduces the number of contaminated eggs, but not indefinitely: the advantage of more frequent sampling is counterbalanced by the cumulative sample including less recently laid eggs. Apparently, optimizing surveillance has its limits when test specificity is taken into account.