Fluctuating food supply affects the clutch size of Tengmalm's owl independent of laying date

Summary In western Finland, yearly median laying dates of Tengmalm's owls varied from 14 March to 27 April during 1973–1989 and were negatively correlated with the winter densities of voles. Yearly mean clutch sizes varied from 4.0 to 6.7 and were more closely related to the spring than to the winter densities of voles. The yearly mean clutch size decreased with yearly median laying date. The 3-year vole population cycle is typical of the study area. The start of egg-laying was earliest in the peak phase of the cycle (median laying date 22 March), when vole numbers are high during egg-laying, but decline rapidly to low numbers in the next autumn or winter. In the increase phase (1 April) vole abundances are moderate at the time of laying, but increase to a peak in the next autumn or winter. In the low phase (15 April) voles are scarce in spring and in the preceding winter, starting to increase in late summer. Clutch size and female body mass were independent of laying date in the low phase, decreased slowly but significantly in the increase phase, and declined abruptly in the peak phase. These trends also held when the effects of territory quality, female age and male age were ruled out. When comparing the same laying periods, clutch sizes were significantly larger in the increase than in other phases of the cycle, but there was no difference between the peak and low phases. Supplementary feeding prior to and during egg-laying increased clutch size independent of laying date. These results agreed with the income model (the rate of energy supply during laying determines clutch size). Tengmalm's owls invest most in a clutch in the increase phase, as the reproductive value of eggs is largest because of high survival of yearlings. A high reproductive effort may be adaptive during this phase, because the availability of voles is predictable during the laying period.     

Influence of fine-scale habitat structure on nest-site occupancy,laying date and clutch size in Blue Tits Cyanistes caeruleus

Most birds have specific habitat requirements for breeding. The vegetation structure surrounding nest-sites is an important component of habitat quality, and can have large effects on avian breeding performance. We studied 13 years of Blue Tit Cyanistes caeruleus population data to determine whether characteristics of vegetation structure predict site occupancy, laying date and number of eggs laid. Measurements of vegetation structure included the density of English Oak Quercus robur, European Beech Fagus sylvatica, and other deciduous, coniferous and non-coniferous evergreen trees, within a 20-m radius of nest-boxes used for breeding. Trees were further sub-divided into specific classes of trunk circumferences to determine the densities for different maturity levels. Based on Principal Component Analysis (PCA), we reduced the total number of 17 measured vegetation variables to 7 main categories, which we used for further analyses. We found that the occupancy rate of sites and the number of eggs laid correlated positively with the proportion of deciduous trees and negatively with the density of coniferous trees. Laying of the first egg was advanced with a greater proportion of deciduous trees. Among deciduous trees, the English Oak appeared to be most important, as a higher density of more mature English Oak trees was associated with more frequent nest-box occupancy, a larger number of eggs laid, and an earlier laying start. Furthermore, laying started earlier and more eggs were laid in nest-boxes with higher occupancy rates. Together, these findings highlight the role of deciduous trees, particularly more mature English Oak, as important predictors of high-quality preferred habitat. These results aid in defining habitat quality and will facilitate future studies on the importance of environmental quality for breeding performance.     

The effect of migration strategy and food availability on White Stork Ciconia ciconia breeding success

In the mid 1970s, the breeding populations of the migrant White Stork Ciconia ciconia were close to extinction in the northeastern region of France (Alsace). A re-introduction project was implemented, resulting in the year-round settlement of some individuals in the region, which rely on additional food supplied by humans during the winter. Today, both resident and migrant birds breed in the same areas and take food from rubbish dumps and humans (farmers). The effects of these anthropogenic influences, altering Stork behaviour, on Stork reproductive success are not known. The aim of this study was to test the influence of bird status (resident vs. migrant) and food availability (control nests vs. nests that benefit from high food supply) on reproductive success. In control nests, the mean laying date was earlier in resident than in migrant White Storks. There was also a clear seasonal decline in clutch size. For all nests, the numbers of eggs and hatchlings were higher in resident birds than in migrants, which can be attributed to the earlier breeding of resident Storks. The large broods of resident birds showed a high mortality rate, leading to the same fledgling success (fledglings/hatchlings) and number of fledglings as in migrants. Fledgling success and the number of fledglings were higher for nests close to a reliable food supply. In summary, although resident birds can breed earlier and produce more eggs than migrants, we found no advantage in terms of number of fledglings. The higher mortality rate of chicks found in pairs with a large brood could be caused by the deterioration of their habitat. Thus, the year-round settlement of Storks may not present a biological advantage if the quality of their habitat is not guaranteed by the conservation of their grasslands.     

采用人工孵化及育雏等技术救助东方白鹳的初步探讨

2000年5～7月,在吉林向海国家级自然保护区对弃巢的东方白鹳(Ciconia boyciana)4枚卵进行人工孵化及育雏研究。在孵化期温度37．4～37．6℃,湿度45％～55％;出雏期温度37．2～37℃．湿度60％～65％,同时严格了翻卵、晾卵、通风、换气等技术指标,孵化成功率100％。在设定的温度、湿度、光照及保证食物供给的条件下进行育雏,对l～30日龄的幼雏进行连续的测量及观察,结果表明．幼雏生长发育与野生条件下自然育雏的幼雏生长发育基本相近。     

Intra-seasonal decline of clutch size in Lesser Snow Geese

Summary Different mechanisms proposed to explain the intra-seasonal decline in clutch size of Lesser Snow Geese (Anser caerulescens caerulescens) were tested at the La Perouse Bay colony, Manitoba, Canada. Ovary examination of females collected after laying revealed that the actual number of eggs produced per female decreased over the laying period. This finding eliminates nest-parasitism, partial clutch predation and renesting attempts as sufficient explanations for seasonal clutch size decline. Follicular atresia induced by reserve depletion was also rejected since its occurrence was similar among early and late nesters. The decline in clutch size was observed within age-classes, and therefore age effects on clutch size and laying date per se do not account for the observed relationship. Clutch size and laying date were respectively positively and negatively correlated with the amount of nutrient reserves in females at the onset of laying, and also covaried within individuals observed breeding in several seasons. Laying date repeatability was estimated at 0.22. It is postulated that the seasonal decline in clutch size results mainly from a positive feed-back of female's nutrient reserves on the hormones controlling ovary development. Hatching synchrony or shortness of the breeding season may be the ultimate factors responsible for the intra-seasonal clutch size decline in Lesser Snow Geese.     

A comparative study of egg mass and clutch size in the Anseriformes

The factors explaining interspecific differences in clutch investment in precocial birds are poorly understood. We investigated how variations in clutch characteristics are related to environmental factors in a comparative study of 151 extant species of ducks, geese and swans (Anseriformes). Egg mass was negatively related to clutch size in a phylogenetic regression, a relationship that was much stronger when controlling for female mass. Nest placement was related to both egg size and clutch size, with cavity-nesting species laying more but smaller eggs. Egg size was positively correlated with incubation period and with female mass, and also with sexual size dimorphism (i.e. male mass relative to that of the female). Clutch size was not related to female mass. Species with long term pair bonds laid smaller clutches and larger eggs. The size of the breeding range was strongly positively correlated with clutch size and clutch mass, and its inclusion in multivariate models made other biogeographical variables (hemisphere, breeding latitude or insularity) non-significant. The small clutches in insular species appear to be a product of small range size rather than insularity per se. Our results suggest there is an evolutionary trade-off between clutch and egg size, and lend support to Lack’s resource-limitation hypothesis for the waterfowl.     

Experiments on clutch size and nest size in passerine birds

Summary Results of experiments on three passerine species suggest that brood size may be constrained by nest size, since the breeding success of pairs provided with large nestcups was greater than that of those provided with small artificial nestcups. These results may have important implications, e.g. to the design of experiments involving manipulation of clutch and brood size. A small nestcup is requisite for successful hatching during the incubation period, but a large one for successful rearing during the nestling period. In nature this difference may select for types of nesting materials that are elastic, such as mosses and lichens. However, experiments showed that such materials rapidly absorb rainwater but only slowly dry out. In addition, because large nests dry out more slowly than small nests, selection will favour small nests among those open-nesting species that have exposed nests. A further possible nest size constraint on open-nesters is nest predation. However, no difference in the predation rate was found in experiments with small and large artificial nests.     

On the evolution of clutch size and nest size in passerine birds

Summary I examined the hypothesis that the clutch size of some altricial birds may be limited by over-crowding of the nestlings in the nest, by comparing data on different species of European passerines. Large-sized birds build, relative to the body, larger nests than small-sized birds, both as regards the inner and the outer nest widths and as regards edge breadth; only inner nestcup depth did not change relatively to body size. Nest size also varied in relation to nesting place. Birds with open nests built off the ground had a rather narrow nestcup, whereas those with a domed nest, or which nest in a cavity, had a wide nestcup. When only open-nesters were compared, birds nesting on, or close to, the ground tended to have a wider nestcup than birds nesting above the ground. Inner nestcup width was correlated with the amount of mosses and lichens used in building the nest; the more of such materials the narrower the nestcup. The three variables: standardised body size, nesting place, and type of nesting material used accounted for 92% of the overall variation observed in inner nestcup width. When controlling for adult body size, clutch size was positively correlated with the size of the nestcup. A multiple regression analysis showed that relative nestcup depth, nest site, and type of nesting materials used, accounted for 64% of the overall variation in clutch size.     

Isolation and characterization of a new suite of microsatellite markers in the European White Stork, Ciconia ciconia

The White Stork (Ciconia ciconia) has an extensive European breeding distribution. There have been significant demographic changes since the 1930s, with country-specific extinctions throughout the western distribution since the mid-1940s. Following various reintroduction programs significant concerns have been raised about the geographic origins of introduced storks, and the effect this may have on individual biology, particularly breeding success. Here we report on seven new microsatellite markers developed for C. ciconia that have been successfully combined in a series of multiplex PCR’s with six markers previously described for the Wood Stork.     

Annual variation in the seasonal shift in egg size and clutch size in Sceloporus woodi

Summary Early and late season clutch parameters were examined over a three year period in the Florida scrub lizard, Sceloporus woodi. Precipitation levels were monitored throughout the study. In the early and late season of 1984 and the early season of 1986 precipitation levels approximated long-term mean levels of precipitation. In 1985 a severe winter drought occurred. Clutch size was positively related to body size in all samples in every year. In 1984 and 1986, egg size was not related to clutch size, whereas, in 1985 egg size was negatively related to clutch size. In 1985, females produced large clutches of small eggs early in the season and small clutches of large eggs late in the season. In 1984, no seasonal changes in egg or clutch size occurred. In the late season of 1986, females produced the largest clutches and the smallest eggs of all the samples, but egg and clutch size were not statistically different from the early season egg and clutch size of 1986. Total clutch dry weight, an estimate of total clutch energy, was not different in any of the six sampling periods. These data do not support current adaptationist models that attempt to explain the control of clutch and egg size in lizards. It is argued in this paper that egg and clutch size may vary in response to past environments that affect a female's physical condition, as well as, current resources that may be important for maintenance and reproduction. Egg and clutch size appear to be plastic traits selected to respond to proximal environmental variation, whereas, the investment of total dry matter/clutch has been optimized.     

The effect of climate change on the correlation between avian life-history traits

The ultimate reason why birds should advance their phenology in response to climate change is to match the shifting phenology of underlying levels of the food chain. In a seasonal environment, the timing of food abundance is one of the crucial factors to which birds should adapt their timing of reproduction. They can do this by shifting egg‐laying date (LD), and also by changing other life‐history characters that affect the period between laying of the eggs and hatching of the chicks. In a long‐term study of the migratory Pied Flycatcher, we show that the peak of abundance of nestling food (caterpillars) has advanced during the last two decades, and that the birds advanced their LD. LD strongly correlates with the timing of the caterpillar peak, but in years with an early food peak the birds laid their eggs late relative to this food peak. In such years, the birds advance their hatching date by incubating earlier in the clutch and reducing the interval between laying the last egg to hatching of the first egg, thereby partly compensating for their relative late LD. Paradoxically, they also laid larger clutches in the years with an early food peak, and thereby took more time to lay (i.e. one egg per day). Clutch size therefore declined more strongly with LD in years with an early food peak. This stronger response is adaptive because the fitness of an egg declined more strongly with date in early than in late years. Clearly, avian life‐history traits are correlated and Pied Flycatchers apparently optimize over the whole complex of the traits including LD, clutch size and the onset of incubation. Climate change will lead to changing selection pressures on this complex of traits and presumably the way they are correlated.     

Autumn migration of the White Stork,Ciconia ciconia,and the Black Stork,C. nigra,over the Bosphorus (Aves: Ciconiidae)

The Bosphorus is one of the main migration routes for soaring birds in Europe. Migrating White Storks and Black Storks have been counted at Büyük Çamlica hill in the four autumn seasons of 2006, 2007, 2008 and 2009 for 78 days each year. The numbers recorded are significantly lower than those counted in the1970’s, and it is discussed whether this decline could be related to a change in migration routes caused by an increase in the size of the urban area of the City of Istanbul. The population of Istanbul has increased from 3.0 million in 1970 to 13.2 million in 2010.     

Life-history, genotypic, and environmental correlates of clutch size in the Glanville fritillary butterfly

Abstract.  1. Glanville fritillary butterfly ( Melitaea cinxia ) females lay up to 10 clutches of 50–300 eggs in their lifetime. Clutch size is an important life-history trait as larval group size affects survival throughout larval development.
2. Two experiments were carried out in a large population cage in the field to investigate the life-history and environmental correlates of clutch size.
3. Clutch size decreased with the cumulative number of eggs laid previously, increased with both female body weight and the number of days between consecutive clutches.
4. Genotypic differences among females in the glycolytic enzyme phosphoglucose isomerase had a significant influence on clutch size, partly because females of particular genotypes were able to initiate oviposition earlier in the day and thereby take advantage of the most favourable environmental conditions for oviposition.
5. Factors influencing clutch size were partly different in two summers, indicating the modulating effect of prevailing environmental conditions on reproductive performance.     

It takes two: Heritable male effects on reproductive timing but not clutch size in a wild bird population*

Within-population variation in the traits underpinning reproductive output has long been of central interest to biologists. Since they are strongly linked to lifetime reproductive success, these traits are expected to be subject to strong selection and, if heritable, to evolve. Despite the formation of durable pair bonds in many animal taxa, reproductive traits are often regarded as female-specific, and estimates of quantitative genetic variation seldom consider a potential role for heritable male effects. Yet reliable estimates of such social genetic effects are important since they influence the amount of heritable variation available to selection. Based on a 52-year study of a nestbox-breeding great tit (Parus major) population, we apply “extended” bivariate animal models in which the heritable effects of both sexes are modeled to assess the extent to which males contribute to heritable variation in seasonal reproductive timing (egg laying date) and clutch size, while accommodating the covariance between the two traits. Our analyses show that reproductive timing is a jointly expressed trait in this species, with (positively covarying) heritable variation for laydate being expressed in both members of a breeding pair, such that the total heritable variance is 50% larger than estimated by traditional models. This result was robust to explicit consideration of a potential male-biased environmental confound arising through sexually dimorphic dispersal. In contrast to laydate, males’ contribution to heritable variation in clutch size was limited. Our study thus highlights the contrasting extent of social determination for two major components of annual reproductive success, and emphasizes the need to consider the social context of what are often considered individual-level traits.     

Retrospective Estimation of Genetic Diversity of an Extinct Oriental White Stork (Ciconia boyciana) Population in Japan Using Mounted Specimens and Implications for Reintroduction Programs

The Japanese regional population of the Oriental white stork (Ciconia boyciana) became extinct in 1986. Mitochondrial DNA (mtDNA) D-loop region from 20 mounted specimens preserved at public facilities in Toyooka City, Hyogo Prefecture, Japan and its vicinity (n = 17), the area inhabited by the last of the Japanese population, and samples originating from China (n = 3) which were kept at a zoo was analyzed. After extracting DNA from small pieces of skin from mounted specimens, a 1210-bp region of the mtDNA D-loop region was analyzed. The haplotypes among 11 specimens of storks captured or found dead at Toyooka City just before the population became extinct were completely identical. Four haplotypes observed among the mounted specimens preserved in the vicinity of Toyooka City were differentiated from those of captive storks originating from China and Russia in a previous study. Therefore, the last Japanese population might have been a genetically unique group. However, phylogenetic analysis using the maximum likelihood method showed that haplotypes found in the Japanese regional population were closely related to the Chinese and Russian lineages (sequence difference = 2.1%). One mounted specimen collected in 1935 at Izushi village, in the vicinity of Toyooka City, showed the same haplotype as the captive storks from China, suggesting that genetic flow may have historically occurred between the populations of Japan and the continent. Recently, reintroduction for the Oriental white stork has been planned in Toyooka City. The planning for the recovery of extinct populations should not only involve translocation of species to the range from which it disappeared, but also reconstruction of regional populations while considering the genetic lineage between the extinct and introduced populations.     

Effect of habitat, date of laying and density on clutch size of the Great Tit Parus major in northern Finland

The sizes of 1034 Great Tit clutches were studied at the Oulu area (c. 65°N, 25°30'E) in northern Finland. The average size was 9.86 eggs in the first clutch and 7.51 in the second in 13 study areas. The decrease in clutch size from the first to the second laying was most pronounced in those females laying the largest first clutches.
Irrespective of habitat, the clutch size was larger in the sparsely populated areas than in the densest area (Taskila). The clutch size decreased according to the season in all the areas, but this was not as pronounced in Taskila as in the other areas.
The annual average size of the first clutches was inversely related to the breeding density and pronouncedly so to the mean dale of laying. The latter was suggested to be an adaptation to the short season in the northern areas.
An analysis of data from 27 study areas in Europe, north of the Mediterranean region, suggests that the clutch size does not vary with latitude or longitude.     

Effects of nest-site availability and distribution on density-dependent clutch size and laying date in the Chough Pyrrhocorax pyrrhocorax

We compared the breeding phenology and clutch size of Choughs Pyrrhocorax pyrrhocorax in three Spanish areas that differed in feeding habitat, breeding environmental conditions and the distribution and availability of different nesting sites (cliffs or artefacts). The variation in the timing of laying seemed to be related to differences in climatic conditions determined by the altitude. The variation in clutch size was associated with the different use that Choughs made of the feeding areas because of the contrasting availability and distribution of their nesting sites. Within southeastern Madrid, clutch size of the Chough decreased and its variance increased at high nest densities on cliff sites, suggesting that density dependence in fecundity arises from habitat heterogeneity rather than by interference. At high densities, individuals, territories, nest sites or a combination of these may differ in quality, thus promoting differences and increasing the variance in the initial investment of reproductive effort. The syncronization of the onset of laying at increased breeding densities suggests that social influences arising from communal foraging or avoidance of predation by early warning and predator swamping may be acting also. We suggest that nest-site availability and distribution have a major influence on the social organization of Choughs through their breeding and foraging strategies.     

Egg development time in the Zebra Finch Taeniopygia guttata varies with laying order and clutch size

As female birds are able to lay no more than a single egg each day, in those species producing larger clutches the first laid eggs may get a developmental head‐start over later eggs in the clutch. All other things being equal, the differential pattern of development across the clutch may contribute to hatching asynchrony and subsequent inequity in the competition between brood mates, and ultimately increase variance in the quality and fitness of first‐ and last‐laid offspring. It has been suggested that females might allocate resources differently across the laying sequence to moderate the developmental rate and hatching time of different embryos. We tested this theory in the Zebra Finch Taeniopygia guttata, a common model species for investigating maternal effects in birds. We removed 758 eggs from 160 nests shortly after they were laid and used artificial incubators to control for parental effects and monitor hatching times. Eggs from larger clutches consistently hatched sooner than those from average‐sized clutches, demonstrating that the intrinsic properties of an egg can alter the developmental time of embryos. There were also differences in the development time of eggs across the laying sequence, but these patterns were weaker, inconsistent and unrelated to sequential investment across the laying sequence in a straightforward way. This study indicates that maternal resource allocation to eggs across the laying sequence and across clutch sizes can influence development times and play a potentially important role in determining the competitive dynamics of broods.