Differences In Egg Mass Research Articles

The Quality of Japanese Quail Eggs After Administration of Bifidobacterium sp. and Guazuma ulmifolia Leaf Extract

This study aimed to determine the effect of Bifidobacterium sp. and Guazuma ulmifolia leaf extract on Japanese quail egg production, including egg mass, haugh unit (HU), and egg yolk colour. A total of 96 quails were in the early stages of production, which were randomized into four treatments and six replications. The treatments were (T0) without Bifidobacterium sp. and G. ulmifolia leaf extract, (T1) 0.2% Bifidobacterium sp., (T2) 0.2% G. ulmifolia leaf extract, and (T3) 0.2% Bifidobacterium sp. + 0.2% G. ulmifolia leaf extract. Egg mass data was collected in the third and fourth week of the treatment period, while the HU data and egg yolk colour were carried out on the last week of the treatment period. The treatment groups showed significant differences in egg mass. Groups T2 and T3 showed significant differences in egg yolk colour. The combination of feed additives can increase the value of HU but not significantly (p>0.05). In conclusion, the combination of 0.2% Bifidobacterium sp. and 0.2% G. ulmifolia leaf extract in drinking water can produce the highest egg quality.

Strong decrease in egg mass on subsequent days of oviposition generates little variation in offspring performance in the pine‐tree lappet moth, Dendrolimus pini

AbstractThe pine‐tree lappet moth, Dendrolimus pini (L.) (Lepidoptera: Lasiocampidae), is a pest whose natural range mostly follows that of its host, Scots pine, Pinus sylvestris L. (Pinaceae). Under natural conditions, we observed differences in larval body size, pointing to different rates of their growth and development. This study aimed to check whether differences in egg mass can differentiate the growth and development rate of D. pini larvae. We assumed that decrease in egg mass on subsequent days of oviposition can have a large impact. Our results indicate that there is an unusually strong fecundity advantage of large female mass in D. pini, but with each day of laying, the mean mass of the eggs decreases. However, offspring phenotype and development in D. pini is not clearly correlated with egg mass. We also confirmed a strong decrease in the number and mass of eggs on subsequent days of oviposition. However, egg mass decline did not correspond with the performance of the offspring in a laboratory rearing because the specimens formed from ‘medium‐mass’ eggs were characterized by the highest fitness. Although we noted a significant impact of the day of oviposition on some offspring's fitness parameters (e.g., development stage duration, pupal mass, adult mass), the variation was not large. The offspring hatched from eggs on the 3rd day of oviposition were characterized by increased values of some parameters (e.g., higher mass, heavier cocoons, faster development). Variation in the development of the larvae could be a strategy to help offspring survive under short‐term unfavorable conditions, and also reduces intra‐species competition which is generally beneficial.

Bazı havuç çeşitlerinin kök-ur nematodu türlerine (Meloidogyne spp. Goeldi, 1982) karşı reaksiyonu

Kök-ur nematodlarının diğer sebzelerde olduğu gibi havuç bitkisinde de önemli verim kayıplarına yol açtığı bilinmektedir. Bu çalışmada İç Anadolu Bölgesi’nde ticari olarak yaygın şekilde kullanılan üç farklı havuç çeşidinin dört farklı kök-ur nematodu türüne karşı reaksiyon durumları 2018 yılında iklim odasında saksı denemeleri ile değerlendirilmiştir. Köklerde oluşan ur ve yumurta paketi sayılarına göre Romance, Chantenay, Nantes çeşitleri Meloidogyne chitwoodi, M. javanica, M. incognita ve M. hapla’ya karşı hassas bulunmuştur. Meydana getirdikleri yumurta paketi ve gal sayılarına göre M. chitwoodi ve M. incognita türlerinde, çeşitler arasında fark tespit edilmemiştir (P>0.05). M. javanica türünün 234.4 adet yumurta paketi ve gal ile en fazla Nantes çeşidinde; M. hapla’nın ise 193.6 adet ile en fazla Nantes çeşidinde çoğaldığı belirlenmiştir (P<0.05). Çeşitler açısından ise Chantenay çeşidinde türler arasında fark tespit edilmemiş olup (P>0.05), Nantes çeşidinde M. javanica (234.4) ve M. hapla (193.6), Romance çeşidinde ise M. javanica (207.8), M. hapla (176.4) ve M. chitwoodi (141.6) türleri aynı grupta yer almıştır (P<0.05). Çalışma sonucunda Romance, Chantenay ve Nantes havuç çeşitlerinin kök-ur nematodlarına hassas olduğu ve bulaşık alanlarda bu çeşitlerin kullanımında dikkatli olunması gerektiği sonucuna ulaşılmıştır.

Effect of Housing System and Rosemary and Cinnamon Essential Oils on Layers Performance, Egg Quality, Haematological Traits, Blood Chemistry, Immunity, and Antioxidant.

Simple SummaryThe current study aimed to investigate the effects of a housing system, and dietary supplementation of rosemary and cinnamon essential oils on layers performance and egg quality. A factorial arrangement (2 × 3) was performed including two housing systems (floor and cage) and three different types of essential oils (0, 300 mg/kg diet of rosemary and 300 mg/kg diet of cinnamon essential oils) to study their effects on the productive performance, egg quality, immunity, oxidative stress and haematology of laying hens during the production stages. The data suggested that the supplementation of rosemary and cinnamon essential oils in laying hen diet showed significant positive effects on hen performance and egg production. Additionally, the different housing systems did not result in any positive or negative impact on these traits.Housing system and nutrition are non-genetic factors that can improve the well-being of animals to obtain higher quality products. A better understanding of how different housing systems and essential oils can influence the performance of layers is very important at the research and commercial levels. The current study aimed to investigate the effects of a housing system and dietary supplementation of rosemary and cinnamon essential oils on layers’ performance and egg quality. A factorial arrangement (2 × 3) was performed include two housing systems (floor and cage) and three different types of essential oils (0, 300 mg/kg diet of rosemary and 300 mg/kg diet of cinnamon essential oils) to study their effects on the productive performance, egg quality, immunity, oxidative stress and haematology of ISA brown laying hens during the production stages (from 28 to 76 weeks of age). Birds were randomly divided into two groups each comprising of 1500 birds; the first group was moved from the litter to reared laying cages while the second group was floor reared. Each group was randomly divided into three groups, the first was considered as a control group, the second treated with rosemary essential oil, and the third with cinnamon essential oil. The differences in egg production and weight, egg quality, feed intake and conversion, blood picture and chemistry, immunity, and antioxidant parameters between the different housing systems (floor and cage) were not significant at (p < 0.05 or 0.01). On the other hand, the egg production and weight, Haugh unit, feed intake and conversion, blood cholesterol, Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST), urea, Ca, P, immunity, and antioxidant parameters were significantly (p < 0.05 or 0.01) better in rosemary and cinnamon groups than in the control group. Furthermore, the results of dietary supplementation with rosemary and cinnamon were very close. Regarding egg production and weight, there were no significant differences due to the interactions. The differences in egg mass among the interactions were also not significant except at 68–76 weeks, where the cage × cinnamon group was the highest. Under the floor rearing system, birds that were fed a diet supplemented with or without essential oils (EOs) consumed more feed than those raised under the cage system. Regarding feed conversion rate (FCR), the differences among the interactions were not significant except at 44–52, 52–60 and 68–76 weeks, where the cage × cinnamon group was the lowest. Excluding glutathione peroxidase (GPx) activity (p < 0.001), all immunity and antioxidant indices were not statistically different as a consequence of the interaction among EOs and housing systems. Additionally, the highest levels of phosphorus were observed for layers fed diets enriched with cinnamon oil with the cage or floor system. In conclusion, the data suggested that supplementation of rosemary and cinnamon essential oils in laying hen diet showed significantly positive effects on hen performance and egg production. Cholesterol, liver and kidney functions, immunity, and antioxidant parameters improved with rosemary and cinnamon supplementation when compared to the control. Additionally, the different housing systems did not result in any positive or negative impact on these traits.

Vitamin D fortification of eggs for human health

Vitamin D is an essential component of vertebrate nutrition, and epidemiological surveys confirm a chronic vitamin D insufficiency in the human population. Eggs are one of the few natural sources rich in vitamin D, containing both vitamin D₃ (D₃) and 25-hydroxyvitamin D₃ (25(OH)D₃). 25-Hydroxyvitamin D₃ is especially useful because it provides five times the relative biological activity of vitamin D. In order to establish the potential for enrichment of eggs with D₃ and 25(OH)D₃, a total of 162 hens were fed three levels of D₃ in combination with three levels of 25(OH)D₃. Egg yolks were analysed for their D₃ and 25(OH)D₃ contents, and egg production, egg weights and feed efficiencies were recorded. The contents of D₃ and 25(OH)D₃ in egg yolk increased significantly with increasing dietary concentrations. There were no significant differences in egg mass, egg weight or feed efficiency. Depending on the dietary concentrations used, it was possible to produce eggs with between 100 and 500 IU vitamin D, providing scope to meet the recommended daily requirement of vitamin D for children or adults. The addition of higher levels of D₃ and 25(OH)D₃ produced eggs with sufficient vitamin D to meet the recommended daily requirements of adults and children without any detrimental effect on production parameters.

Evaluation of limit feeding corn and distillers dried grains with solubles in non-feed-withdrawal molt programs for laying hens

An experiment was conducted using 504 Hy-Line W-36 Single Comb White Leghorn hens (69 wk of age) randomly assigned to 1 of 7 treatments. These treatments consisted of a 47% corn:47% soy hulls diet (C:SH) fed ad libitum; a 94% corn diet fed at a rate of 36.3, 45.4, or 54.5 g/hen per day (CORN 36, CORN 45, and CORN 54, respectively); and a 94% corn distillers dried grains with solubles (DDGS) diet fed at the same rates as the previous corn diets (DDGS 36, DDGS 45, and DDGS 54, respectively) during the molt period of 28 d. The intent was to feed the DDGS diets for 28 d; however, all hens on these diets had very low feed intakes and greater than anticipated BW loss. Thus, they were switched to a 16% CP corn-soybean meal layer diet on d 19 of the molt period. At d 28, hens on all treatments were fed the same corn-soybean meal layer diet for 39 wk (73 to 112 wk of age). All DDGS diets and the CORN 36 diet resulted in total cessation of egg production during the molt period and egg production of hens fed the CORN 45, CORN 54, and C:SH diets had decreased to 3 and 4%, respectively, by d 28. Body weight loss during the 28-d molt period ranged from 14% for the CORN 54 diet to approximately 23% for the 3 DDGS diets. Postmolt egg production (5 to 43 wk) was higher for hens fed the DDGS molt diets than those fed the corn diets. There were no consistent differences in egg mass, egg-specific gravity, feed efficiency, or layer feed consumption among molt treatments for the postmolt period. These results indicate that limit feeding corn diet and DDGS diet in non-feed-withdrawal molt programs will yield long-term postmolt performance that is comparable to that observed by ad libitum feeding a C:SH diet.

Using different ratios of bitter vetch (Vicia ervilia) seed for moult induction and post-moult performance in commercial laying hens

1. The applicability of different ratios of bitter vetch seed as a new method for moult induction in laying hens was studied. The effectiveness of bitter vetch seed on post-moult production and post-moult egg quality was also investigated. 2. A total of 120 Single Comb White Leghorn hens, 78 weeks of age, were used in this study. The hens were randomly assigned to 5 treatment groups of 24 birds each. The treatments were 30% bitter vetch seed (BV30) diet, 60% bitter vetch seed (BV60) diet, 90% bitter vetch seed (90BV) diet, feed withdrawal method (FW) and full-fed non-moulted control (CON). 3. Egg production ceased first in FW and BV90 treated hens and last in BV30 treated hens. As the percentage of bitter vetch seed increased in the moulting ration, feed intake decreased and body weight loss increased during the 10-d moult induction period. Time to first egg production was significantly greater in hens exposed to the FW and BV90 diets. 4. FW and BV90 treatment hens had significantly higher hen-d egg production than non-moulted control hens. Egg weight was significantly higher in BV30 and BV90 treatments. There were no differences in egg mass, feed intake and mortality among experimental treatments during the post-moult period. 5. No significant improvements were observed in exterior or interior egg quality in moulted hens, except for Haugh units, which were significantly higher in moulted hens when compared to the non-moulted control hens. 6. In conclusion, the present study showed ad libitum feeding of a layer ration with 90% of bitter vetch seed for 10 d proved to be effective for inducing moult, increasing post-moult egg production and improving some internal egg quality parameters.

The hypoxia of high altitude causes restricted fetal growth in chick embryos with the extent of this effect depending on maternal altitudinal status

The hypoxia of high altitude causes restricted fetal growth in chick embryos with the extent of this effect depending on maternal altitudinal status

Pre‐breeding diet affects the allocation of yolk hormones in zebra finchesTaeniopygia guttata

The ability of mothers to modify offspring phenotype to match prevailing environmental conditions is an important component of reproductive success, especially in variable environments. Pre‐breeding conditions, such as food abundance, may have significant consequences for both the number and quality of offspring a female produces as well as her ability to rear the offspring. In an experiment where pre‐breeding diet was manipulated, we investigated if allocation of yolk androgens (testosterone and 5α‐dihydrotestosterone) was related to the quality of diet experienced prior to breeding. Female zebra finchesTaeniopygia guttataproduced larger clutches on high quality diet than on low quality diet but with no differences in egg mass. Yolk androgen levels were repeatable within subsequent clutches of the same female and females did not change mean androgen content in eggs in relation to diet quality. However, within‐in clutch pattern of yolk testosterone and DHT changed with diet treatment. Testosterone and DHT decreased with laying order on the low quality diet but remained constant on the high quality diet. Differential yolk androgen allocation within the clutch may alter the competitive differences between chicks and provide females the possibility to adjust reproductive investment and offspring phenotype already at the egg stage.

Pre-breeding diet affects the allocation of yolk hormones in zebra finches Taeniopygia guttata

The ability of mothers to modify offspring phenotype to match prevailing environmental conditions is an important component of reproductive success, especially in variable environments. Pre-breeding conditions, such as food abundance, may have significant consequences for both the number and quality of offspring a female produces as well as her ability to rear the offspring. In an experiment where pre-breeding diet was manipulated, we investigated if allocation of yolk androgens (testosterone and 5 alpha-dihydrotestosterone) was related to the quality of diet experienced prior to breeding. Female zebra finches Taeniopygia guttata produced larger clutches on high quality diet than on low quality diet but with no differences in egg mass. Yolk androgen levels were repeatable within subsequent clutches of the same female and females did not change mean androgen content in eggs in relation to diet quality. However, within-in Clutch pattern of yolk testosterone and DHT changed with diet treatment. Testosterone and DHT decreased with laying order on the low quality diet but remained constant on the high quality diet. Differential yolk androgen allocation within the clutch may alter the competitive differences between chicks and provide females the possibility to adjust reproductive investment and offspring phenotype already at the egg stage. (Less)

Influence of intraclutch egg-mass variation and hatching asynchrony on relative offspring performance within broods of an altricial bird

Rates of growth and size of nestlings at fledging have important consequences for future survival and reproductive success in many passerine birds. Within broods of altricial species, these characteristics are often influenced by size hierarchies established early in the nesting period due to hatching asynchrony and within-clutch variation in egg mass, but the concurrent effect of these factors is poorly understood. We investigated the relative influence of these variables on nestling performance within broods of tree swallows, Tachycineta bicolor (Vieillot, 1808). Nestlings that hatched earlier within nests were heavier and larger than their later-hatched siblings at 4 days of age. Similarly, earlier-hatched nestlings grew their ninth primary flight feathers faster and had longer ninth primaries just prior to fledging than did later-hatched siblings. Differences in egg mass of siblings also contributed to mass and size hierarchies at 4 days of age, but did not affect any other difference in sibling performance. We conclude that within-clutch variation in performance of offspring is determined primarily by size hierarchies resulting from asynchronous hatching. Intraclutch egg-mass variation appears to have little effect on performance of siblings and may be best explained by proximate constraints on females.

LIFE-HISTORY AND ECOLOGICAL CORRELATES OF GEOGRAPHIC VARIATION IN EGG AND CLUTCH MASS AMONG PASSERINE SPECIES

Broad geographic patterns in egg and clutch mass are poorly described, and potential causes of variation remain largely unexamined. We describe interspecific variation in avian egg and clutch mass within and among diverse geographic regions and explore hypotheses related to allometry, clutch size, nest predation, adult mortality, and parental care as correlates and possible explanations of variation. We studied 74 species of Passeriformes at four latitudes on three continents: the north temperate United States, tropical Venezuela, subtropical Argentina, and south temperate South Africa. Egg and clutch mass increased with adult body mass in all locations, but differed among locations for the same body mass, demonstrating that egg and clutch mass have evolved to some extent independent of body mass among regions. A major portion of egg mass variation was explained by an inverse relationship with clutch size within and among regions, as predicted by life-history theory. However, clutch size did not explain all geographic differences in egg mass; eggs were smallest in South Africa despite small clutch sizes. These small eggs might be explained by high nest predation rates in South Africa; life-history theory predicts reduced reproductive effort under high risk of offspring mortality. This prediction was supported for clutch mass, which was inversely related to nest predation but not for egg mass. Nevertheless, clutch mass variation was not fully explained by nest predation, possibly reflecting interacting effects of adult mortality. Tests of the possible effects of nest predation on egg mass were compromised by limited power and by counterposing direct and indirect effects. Finally, components of parental investment, defined as effort per offspring, might be expected to positively coevolve. Indeed, egg mass, but not clutch mass, was greater in species that shared incubation by males and females compared with species in which only females incubate eggs. However, egg and clutch mass were not related to effort of parental care as measured by incubation attentiveness. Ecological and life-history correlates of egg and clutch mass variation found here follow from theory, but possible evolutionary causes deserve further study.

Population Differences in Pre- and Post-fertilization Offspring Provisioning in the Least Killifish, Heterandria formosa

We used data from a long-term field study of two populations of the Least Killifish, Heterandria formosa, to examine whether genetically based population differences in offspring size at birth are mainly due to differences in pre-fertilization offspring provisioning (i.e., differences in egg mass) or differences in post-fertilization offspring provisioning (i.e., the degree of matrotrophy). We found differences between populations in pre-fertilization offspring provisioning and larger differences in post-fertilization provisioning. These results establish population variation in H. formosa as a potential model for studying the costs and benefits that could modulate the evolution of matrotrophy. In addition, our results illuminate some of the costs and benefits associated with matrotrophy and offer insight into how matrotrophy influences the expression of other life history relationships, including that between female size and fecundity, the trade-off between offspring number and size, and the population-specific responses of offspring number and size to variation in population density.

Mass provisioning to different‐sex eggs within the laying sequence: consequences for adjustment of reproductive effort in a sexually dimorphic bird

Summary In birds, the potential maternal ability to adjust resource allocation to different eggs in the clutch might have a major effect on the survival expectancies of particular nestlings or entire broods. We assessed whether sexually size‐dimorphic Eurasian kestrels Falco tinnunculus (Linnaeus) are able to adjust their reproductive effort by adopting different strategies of egg mass provisioning according to egg sex and laying order. Initial eggs bearing male embryos were heavier than initial eggs bearing female embryos, but no differences in egg mass associated to sex were detected for eggs laid subsequently. Furthermore, in clutches started with a male egg, egg mass declined in subsequent eggs, while in clutches started by a female egg the opposite trend in within‐clutch egg‐mass variation was found. This suggests differential deposition of resources invested in initial eggs of different sex leading to saved or depleted resources for subsequent eggs. Daughters from initial eggs hatched earlier than sons from initial eggs, which may enhance survival of smaller siblings hatched later. These contrasting strategies of egg provisioning and hatching patterns depending on the sex of the first‐laid egg were associated, respectively, with marked mass hierarchies and a lack of mass hierarchies at fledgling in broods initiated with eggs bearing sons and daughters. Parental kestrels may allocate reproductive effort by promoting favouritism towards early hatched chicks or by avoiding any favouritism by producing siblings of each sex with similar mass. This may be achieved depending on the female ability both to identify egg sex and to partially reabsorb or differentially allocate resources to eggs accordingly to adjust reproductive investment. This may be a key mechanism to control sibling competition in birds with sexual dimorphism in mass.

Reproductive Characteristics of the Island Lacertid Lizard Podarcis lilfordi

We report reproductive characteristics (clutch frequency, clutch size, egg and hatchling sizes) of the island lizard Podarcis lilfordi, studied in the laboratory. Individual females produced two or three consecutive clutches, composed of 2-4 eggs with an average mass of 0.63 g. Both clutch size and average egg mass were independent of female body length, and did not differ between the first and subsequent annual clutches. Among-clutch differences in egg mass were negatively correlated with clutch size, and this trade-off is independent of female size. Larger clutches were also composed of less elongated (i.e, rounder) eggs than are smaller clutches, suggesting that limitations posed by the females' body volume, rather than by restrictions of energy availability, induce the phenotypic trade-off between egg size and numbers. Egg shape was also related to female size: larger females laid shorter but wider eggs than smaller individuals, suggesting that egg width is constrained by the width of the female's pelvic girdle. Relative to other Eu- ropean lacertids with similar adult female body length, P lilfordi produces clutches that are composed of very few, but extremely large eggs. Comparative studies of life histories explore patterns of covariation among life history char- acteristics and search for relationships between trait complexes and ecological conditions. Many studies address these issues in reptiles, espe- cially lizards (e.g., Tinkle, 1969; Tinkle et al., 1970; Dunham and Miles, 1985; Dunham et al.,

Reproductive Characteristics of the Lacertid LizardPodarcis atrata

Abstract We report reproductive characteristics (timing of sexual maturity, clutch frequency, clutch size, egg and hatchling sizes) of the Island Lizard Podarcis atrata. Reproductive performance was related to female size. The larger females initiate reproductive activities early in the season and produce two to four clutches annually, whereas the smaller individuals postpone reproduction until the season is well advanced and lay only a single clutch. Clutch size increased with female length and was slightly lower for clutches laid during June–July than for those produced during May. Among-clutch differences in egg mass were negatively correlated with clutch size, and this relationship is independent of female size. Larger clutches are also composed of less elongated (i.e., rounder) eggs than are smaller clutches, suggesting that the phenotypic trade-off between egg size and numbers is induced by limitations posed by the females' body volume, rather than by restrictions of energy availability. Comparison ...

The Effect of Egg Size and Incubation Temperature on Growth in the Turtle, Malaclemys terrapin

We conducted an incubation and rearing experiment to test the effects of incubation tem- perature and egg size on hatchling size and growth of the emydid turtle, Malaclemys terrapin. Eggs from four clutches were assigned randomly to two incubation temperatures, 26 C and 32 C. Half of the hatchlings were sacrificed and sexed after five months and the remainder were raised for three years in a common environment. Similar to other studies of emydid turtles, low and high temperature treatments produced exclusively males and females, respectively. Egg size was more variable among the four clutches than within each clutch. Egg mass accounted for 96% and 97% of the variance in hatchling mass for females and males, respectively. Both clutch and incubation temperature influenced post-hatching growth. The clutch effect was due to both differences in egg mass among clutches and the effects of egg size on hatchling size. Egg mass explained 59% of the variation in size among 3 year old females, but did not explain size variation among 3 year old males. Differences in female growth attributable to egg size could result in as much as a three year difference in age at first reproduction based on the growth trajectories of terrapins from a natural population.

Repeatable Reproduction in Song Sparrows

I looked for evidence of consistent variation in individual quality of breeding females in a population of Song Sparrows (Melospiza melodia). Consistent differences in in3;2;­ dividual quality were detected by looking for correlations in reproductive parameters between nesting attempts. Seven reproductive traits were examined for evidence of variation in in3;2;­ dividual quality. In addition, I determined whether the degree of repeatability was affected by differences in conditions among years, by female age, or by success of previous nesting attempts. There were consistent differences among females in the date of initiation of nesting, clutch size, egg mass, and nutritional condition of offspring. The differences in egg mass between females may be heritable. There was evidence that repeatability of nestling condition is influenced by the success of previous nesting attempts. Although consistent differences were found in quality of female sparrows, there were no "superparents." Females that were good at one given aspect of reproduction were not proficient at all facets of reproduction.

Development of the chick embryo: effects of egg mass

We asked to what extent, within a species, differences in egg mass, hence in eggshell surface area and O 2 conductance, could affect the development of the avian embryo. Large (L, about 70 g) and small (S, about 55 g) fertile chicken eggs were simultaneously incubated and the embryos studied at day 18, i.e. before the onset of lung ventilation. Embryo mass and O 2 consumption (V̇ O 2 ) (measured with a manometric technique) normalized per mass of the freshly laid egg were higher in S than in L, while no differences occurred after normalization by egg surface area (S.A.). Egg water vapour conductance, which is proportional to O 2 conductance, was also found to be directly proportional to egg S.A. Hence, the mass and V̇ O 2 of the embryo are more closely related to the O 2 conductance of the eggshell than to egg mass, giving support to the concept that the avian embryo's V̇ O 2 is not an invariable species characteristic, but a variable dependent on O 2 availability. Hatching and viability did not differ between L and S, and the specific mass of heart and lung and their cellular (DNA) concentration were also similar between the two groups of embryos. Therefore, differentiation of tissues and organogenesis do not seem to be affected by the differences in total O 2 availability determined by the differences in egg mass, while they are probably more important than total tissue mass in setting the time of hatching.

ASPECTS OF THE BREEDING BIOLOGY OF THE AFRICAN BLACK OYSTERCATCHER

Summary Hockey, P. A. R. 1983. Aspects of the breeding biology of the African Black Oystercatcher. Ostrich 54:26-35. Fifty-five pairs of African Black Oystercatchers Haematopus moquini bred at Marcus Island in 1979–1980. Sixteen pairs laid replacement clutches: the mean interval between loss of the fist clutch and laying of a replacement clutch was 22,2 days. Mean inter-nest distance was 19,4 m. The modal clutch size was 2, with a mean of 1.74. Mean dimensions of 105 eggs were 60,7 × 40,l mm and mean fresh egg mass was 55,s g. There were differences in egg mass and dimensions between eggs in one- and two-egg clutches. Rate of egg loss was high, due mainly to depredation by Kelp Gulls Larus dominicanus promoted by human disturbance. Fledging success was lower at a disturbed site than at undisturbed sites, with highest chick mortality occurring in the first week of life. Mortality of first-year birds of eight days and older was estimated at 48% and 69% in two successive seasons. All juvenile birds dispersed...