Egg variability and hatching success in the Cape petrel Daption capense at Nelson Island, South Shetland Islands, Antarctica

Eggs of the Cape petrel Daption capense at Nelson Island, South Shetland Islands, Antarctica, exhibited high variability in volume between females (up to 48%), while for each individual female, both volume and shape of eggs were highly correlated over two seasons. Both female size and body-condition at laying were unrelated to egg-volume in the 'good'season 1991, but larger females produced larger eggs in the 'bad'season 1990, when eggs were smaller on average. In 1991, females in better body-condition, but not larger, started laying earlier. In spite of synchronized laying (75% of eggs laid within five days), egg-volume decreased with laying date. Egg-volume differed significantly between the two years, which could not be explained by changes in the breeding population or timing of breeding. The laying of relatively small eggs and low overall breeding success in 1990 most probably reflected changes in food availability. Overall hatchability was 88% and did not differ significantly between disturbed and control colonies in 1991. Larger and more rounded eggs showed better hatching success, but hatchability was related more to egg-volume whereas hatching rate was related more to egg-shape. As the majority of egg losses were attributable to predation, the hatching rate was influenced by parental performance relatively more than by hatchability. Hence the relationship between hatching rate and egg-shape probably reflects improvement in hatching success with female age/experience, whereas the relationship between egg-size and hatchability suggests effect of egg-size independently of parental traits.     

Egg temperature and initial brood patch area determine hatching asynchrony in Magellanic penguin Spheniscus magellanicus

In birds, the adaptive significance of hatching asynchrony has been under debate for many years and the parental effects on hatching asynchrony have been largely assumed but not often tested. Some authors suggest that hatching asynchrony depends on the incubation onset and many factors have been shown to influence hatching asynchrony in different species. Our objective was to analyze the exact timing of the onset of incubation and if this affects hatching asynchrony; and, in addition, which other factors (brood patch development, incubation position, adult body condition, intra‐clutch egg dimorphism, laying date and year) affect hatching asynchrony in Magellanic penguins Spheniscus magellanicus. We first estimated the eggshell temperature at which embryo development starts, with a non‐destructive and novel method. We then recorded individual egg temperatures in 61 nests during incubation, and related them, and other breeding parameters, to hatching asynchrony. We also observed incubation positions in 307 nests. We found a significant positive relationship between hatching asynchrony and the temperature that the first‐laid egg experienced during egg laying and between hatching asynchrony and the initial brood patch area. We also found a negative relationship between hatching asynchrony and the difference in temperature between second and first‐laid eggs within a clutch, measured after the egg‐laying period was finished. We ruled out position of the eggs during incubation, adult body condition, egg volume, laying date, and study year as factors influencing hatching asynchrony. The egg temperature during laying and the difference in temperature between eggs of a clutch are determinants of hatching asynchrony in Magellanic penguins.     

Patterns of variation in size of Boat-tailed Grackle Quiscalus major eggs

Boat-tailed Grackle Quiscalus major eggs averaged 8^.09 g wet weight. Mean egg weight represented 8 05 % of female body weight. Based on egg weight, Grackle eggs have a shorter incubation period than the general passerine pattern.
Egg weight varied significantly with sequence of laying and between clutches in both two-egg and three-egg clutches. Last laid eggs weighed less than first laid eggs. The mean weight of the first two eggs laid in three-egg clutches did not differ from the mean egg weight of two-egg clutches. The average clutch of two and three eggs weighed 16.33 g and 24.16 g, respectively.
Mean egg weight varied between study colonies and with season. Grackles at East Lake laid eggs that weighed less than grackles at either Alligator Lake or North Lake. Eggs laid during March averaged less than eggs laid later in the season. The locality variation reflects the different timing of nesting between sites rather than food abundance. As nutrient provisioning increases with an increase in egg weight, the seasonal change in egg weight probably reflects improved feeding conditions for the female. This suggests that selection favours beginning laying before reserves of the female are sufficient to lay the largest egg possible.
The size of the young at hatching was correlated with egg size. Newly hate had young averaged 79.6% of fresh egg weight. Egg weight did not determine the probability of hatching or starvation of the young. Females do not appear to adjust egg size facultatively depending on the sex of the young. Eggs producing males and females did not vary significantly in weight, whether comparisons were made within or between clutches.     

Differential predation by mammals and birds: implications for egg-colour polymorphism in a nomadic breeding seabird

Selection for crypsis in varying environments has long been established as the main evolutionary force promoting the huge variation in avian egg coloration. In several avian species, variation in egg coloration exists, but available information available on the relative success of these different colour morphs against predation is scarce. We investigated the value of eggshell coloration against mammal and avian predators in the South American Tern, Sterna hirundinacea. We found evidence of a relationship between particular eggshell ground coloration and success against predation, in different tern colonies, where strong selection was caused by single avian and mammalian predator species. Survival to hatching of eggs with greenish ground coloration was greater than in eggs of the remaining colours when a mammalian carnivore was present. This implies that the human visual system does not accurately represent predator perception but that, viewed through the predator's eyes, the conspicuous greenish eggs are well concealed. The rate of artificial nest predation by visually searching gulls was higher for eggs more conspicuous to the human eye than for eggs more closely resembling the nest substrate. The evolution of polymorphisms in eggshell ground colour may have resulted from differences in the type of predator present, and differences in choice of breeding site varying in the background substrate. The nomadic breeding behaviour of terns may imply that females differing in the frequency of alleles expressing particular egg coloration, selected for in particular environments, may eventually gather in some colonies, thus producing the observed intracolony variation in egg coloration. We hypothesise that egg colour variation could be maintained in the population by shifting peaks of predation impact in the different locations where colonies form, e.g. islands without mammalian predators vs. mainland sites.     

Protoporphyrin‐based eggshell pigmentation predicts hatching success and offspring sex ratio in the barn swallow

Inter‐ and intraspecific variation in eggshell colouration has long fascinated evolutionary biologists. Among species, such variation may accomplish different functions, the most obvious of which is camouflage and background matching. Within species, it has been proposed that inter‐female variation in eggshell pigmentation patterns can reflect egg, maternal or paternal traits and hence may provide cues to conspecifics about egg, maternal or paternal phenotypic quality. However, the relationship between protoporphyrin‐based eggshell pigmentation and egg or maternal/paternal traits appears to be highly variable among species. We investigated patterns of intraspecific variation in Eurasian barn swallow Hirundo r. rustica protoporphyrin‐based eggshell pigmentation, and analysed its association with egg and clutch characteristics, maternal/paternal phenotypic traits and parental feeding effort. Eggshell pigmentation pattern significantly varied between breeding colonies, was significantly repeatable in first clutches laid by the same females in different years (intraclass correlation coefficient ranging between 0.56 and 0.63), but it was not significantly associated with egg traits, such as position in the laying sequence, egg mass, yolk testosterone concentration and antioxidant capacity. It was weakly or non‐significantly associated with female and male traits (sexual ornaments), but females laying darker (higher pigment intensity) first clutches had higher hatching success, suggesting that eggshell pigment intensity may predict fitness. Male nestling feeding effort was not predicted by eggshell pigmentation. In addition, females with darker breast plumage colouration (a melanin‐based trait related to fitness) laid highly protoporphyrin‐covered eggs, suggesting the presence of a previously unappreciated link between protoporphyrin biosynthesis and plumage melanisation. Moreover, the proportion of male offspring increased in clutches originating from highly protoporphyrin‐covered eggs, suggesting that parents could acquire visual cues about their future brood sex composition before egg hatching. Our results support the idea that intraspecific signalling via eggshell pigmentation is a species‐specific rather than a general feature of avian taxa.     

1. A CENSUS AND STUDY OF BIRDS IN ALBANY OPEN THORNBUSHVELD

Williams, A. J. &; Cooper, J. 1983. The Crowned Cormorant: breeding biology, diet, and offspring reduction strategy. Ostrich 54:213-219.

Crowned Cormorants Phalacrocorax coronatus were studied at Dassen and Marcus Islands. The most frequent clutch was three eggs. Egg size varied within clutches with first-laid eggs being largest and heaviest and subsequent eggs progressively smaller and lighter, The mean laying interval was 2,2 days, the mean laying-to-hatching interval was 23,0 days, and the hatching interval was one day. The normal incubation period was 22.4 days. The weight of hatchings was related to the position of the originating egg in the laying sequence. Chicks were fed within 24 h of hatching. Chick development is described over the first 35 days. One chick could fly at 35 days. Hatching success was 48,2%. Hatching success was greatest in second-laid eggs, least in last-laid eggs. The mean number of chicks hatched at a nest was two. Mean diving time was 23,5 s. Most food was fish, particularly klipfish Clinidae and pipefish Syngnathus, 60–160 mm long. The number of offspring produced can be related to food availability by interaction of difference in egg size, hatching asynchrony, and the preferential feeding by adults of the strongest-begging chick. There is a trend towards producing two chicks, normally those from the first two eggs to be laid.     

Egg quality of Japanese quail depends on layer age and storage time

The aim of the study was to analyse egg quality changes of Japanese quail during the reproductive season and after several days of storage. A significantly higher egg weight was recorded in week 9 than in week 25 and week 31 of age ofbirds. The egg specific gravity value of eggs also decreased with the age of quails. The smallest yolk weight and its percentage proportion in egg mass were observed in week 25. Eggs laid in weeks 9 and 25 were characterised by similar and lower (P < or = 0.05) white weight in comparison to those examined on the last date. The highest white proportion in egg weight was recorded during the 25th week. The value of this trait was similar or smaller on the remaining dates. Similar and lower values of the white index and Haugh units, in comparison with the first date, were determined in eggs laid on weeks 25 and 31, whereas similar and greater eggshell thickness than in the 9th week of age was recorded on the last two dates of examination. Lower (P < or = 0.05) egg weight was observed after 5 and 8 than after 0 (measured on the day of laying) days of storage. Likewise, smaller egg specific gravity was recorded after three consecutive periods of storage in comparison with the eggs examined on the day of laying. Eggs examined after 3, 5 and 8 days of storage, in comparison with those stored for 0 days, were characterised by lower yolk index. Significantly smaller weight and white index than after 0 days were determined in eggs stored, respectively, for 5 and 8 as well as for 3, 5 and 8 days. Similarly, smaller numbers of Haugh units were determined after 3 consecutive storage periods in comparison with the eggs examined on the day of laying. Eggs stored for 0 and 3 days were characterised by a greater eggshell weight than those examined after 5 and 8 days. The weight of Japanese quail eggs decreased significantly from day 5 onwards, whereas the egg specific gravity-- from the 3rd day of storage. Yolk and white quality began to deteriorate already after 3 days of egg storage. It appears, therefore, that egg storage of Japanese quails before hatching lasting more than 3 days in the analysed conditions deteriorated the eggshell quality and internal egg traits.     

Testing the relationship between clutch size and brood size in the Coot (Fulica atra)

The time between egg laying and chick fledging is of crucial importance for the survival of young birds. I analyzed breeding output at consecutive phases of growth of young Coots (Fulica atra) relative to the clutch size and laying date. Considering the specific breeding biology of the Coot, I tested whether chick survival reveals clutch size-dependent variability. Clutch size did not affect hatching success; it only affected brood size, and that merely temporarily. During the first 20 days after hatching, i.e. during the time of the highest chick mortality, birds with larger clutches lost chicks at a higher rate. As a result, the number of fledged chicks was independent of the initial number of chicks, and pairs with different clutch sizes had a similar number of fledglings. The laying date had no effect. This pattern of age-related chick survival points to the greater role of the type of chick growth (semi-precocial) and behavior in their survival.     

PARENTAL QUALITY AND SELECTION ON EGG SIZE IN THE MAGELLANIC PENGUIN

We examined the relative contributions of egg size and parental quality to hatching success, fledging success, and chick growth in the Magellanic penguin (Spheniscus magellanicus) be exchanging clutches between nests to reduce the covariation between egg and parental factors. Among control nests, fledging success increased slightly with egg size. However, the effect of egg size independently of parental quality was limited to an influence on chick mass and size for the first 10 days post-hatching. In contrast, attributes of the parents influenced nesting success and chick size at fledging, independently of the egg size actually raised. We suggest that the common occurrence of a positive phenotypic correlation between egg size and fledging success is due to two factors: (1) adults laying large eggs tend to be of higher quality; and (2) to the extent that egg size does influence early survival independently of parental quality, the effect on survival is due to a maternal effect on egg composition rather than an inherent effect of egg size.     

Egg-size variation and reproductive success in the Herring Gull Lams argentatus: adaptive or constrained size of the last egg?

Herring Gull Larus argentatus eggs from a study colony in the Baltic showed a slight but significant variation in egg size within the laying sequence. Last-laid eggs were only about 5% smaller by volume than first eggs. There was no significant difference in dry yolk weight or dry albumen weight, although possible differences were evident. The chicks had nearly equal hatching weights and equally long tarsi. There was no differential mortality in the third chick in the study colony, and there were no indications of egg-size-mediated mortality. The birds in the colony produced an average of 1.45 fledglings per pair. Compared with several other studied colonies, the difference in egg size within a clutch was low, and a comparison of colonies from northwestern Europe suggests that variance within the clutch is negatively correlated with fledging success, so that a large difference in size between first and last eggs is associated with low fledging success. We suggest that the size of the last egg in the clutch reflects the feeding potential in the environment and is mainly a nonadaptive response to poor feeding conditions during laying.     

Relationship between breeding activity and rainfall for Swainson's Spurfowl,Pternistis swainsonii,within southern Africa,with specific reference to the Springbok Flats,Limpopo Province,South Africa

We collated the literature available on the breeding activity of the Swainson's Spurfowl Pternistis swainsonii and made use of reliable unpublished reports, nest record cards and field observations within the Springbok Flats, Limpopo Province, South Africa to establish breeding seasons and pairing behaviour. The onset of breeding (egg laying) is closely associated with rainfall, with male gonad development, population density and covey size (pairing behaviour), all correlated with rainfall. Peak breeding activity is from January–April in South Africa, February–May in Zimbabwe and March–June in Botswana. Egg laying has been recorded in all months and sporadic egg laying in the winter months is most likely the result of isolated rainfall. Mean clutch size is 5.2 eggs/hen (n = 140) with an incubation period of 23 days and brood hatching success and chick survival of 69.4% over the southern African sub-region. Current hunting seasons within Limpopo Province are in line with the recommended hunting season for this region and should remain unchanged: 15 June–30 September. The success of this phasianid can be attributed to its extended breeding season, high survival rate of hatchlings and the potential of birds to breed within their first year.     

Intraspecific variation in size and density of Avocet colonies: effects of nest-distances on hatching and breeding success

In many colonial bird species there is considerable intraspecific variation in colony size and inter‐nest distance (colony density). Possible causes of this variation and its effects on hatching success (survival of eggs) and breeding success (probability of a pair raising chicks) were studied in 48 Avocet Recurvirostra avosetta colonies in Schleswig‐Holstein (Germany) between 1991 and 1996. Colony density was influenced by time of year and habitat (categories: island or mainland, close to or far from feeding grounds). Colonies on islands had the highest densities. When all available space at a colony site was used, colonies became very dense (mean nearest‐neighbour nest distance less than 1 m). Colony size (number of clutches) was influenced by time of year, but not by habitat. Hatching success was low in high density colonies and in very low density ‘colonies’ (single nests) and high over a broad range of intermediate nest densities. The low success rate of single nests was caused by a very high predation rate, whereas the low success rate in very dense colonies was caused by a high rate of nest abandonment. Nest abandonment in very dense colonies was associated with a high level of aggressiveness among Avocets during the egg‐laying period. Due to territorial behaviour, Avocets seemed to be expelled from the densest breeding sites. In very dense colonies, high frequencies of clutches of unusual size occurred due to conspecific nest parasitism. The number of Avocets taking part in attacks on potential egg predators was small and (in colonies of more than one clutch) depended neither on colony size nor on colony density. Despite a low hatching success in very dense colonies, individuals breeding in the densest colonies had significantly better chances of raising chicks than Avocets breeding in less dense colonies. Coloniality seemed to be obligatory for Avocets in order to ensure hatching success. The size and density of colonies seemed to be associated with the availability of suitable nesting habitats (islands).     

Penguin Chicks Benefit from Elevated Yolk Androgen Levels under Sibling Competition

Crested penguins (genus Eudyptes) have a peculiar hatching pattern, with the first-laid egg (A-egg) hatching after the second-laid egg (B-egg) and chicks from A-eggs typically having a much lower survival probability. Maternal yolk androgens have been suggested to contribute to the competitive superiority of the B-chick in southern rockhopper penguins Eudyptes chrysocome, given their important role in mediating sibling competition in other species. We therefore increased the yolk androgen levels in freshly-laid eggs and examined the consequences for sibling competition - via effects on embryonic developmental times, chick growth and early survival. We placed one androgen-treated egg and one control egg into each foster nest, matching them for mass, laying date and laying order. The androgen treatment did not significantly affect embryonic developmental times or chick measurements at hatching. However, elevated yolk androgen levels benefitted chick growth in interaction with the number of siblings in a brood. Chicks from androgen-treated eggs had faster growth in the presence of a sibling than chicks from control eggs. Under these circumstances they also had a higher survival probability. Thus maternal androgens appear to reinforce the observed hatching pattern, facilitating brood reduction. This contrasts to most previous studies in other species where yolk androgens have been shown to compensate for the negative consequences of delayed hatching within the brood hierarchy.     

Seasonal variation in reproductive measures of tropical Roseate Terns Sterna dougallih previously undescribed breeding patterns in a seabird

Seasonal variation in egg-laying, egg size, hatching success, hatchling mass, fledging success and chick growth of Roseate Terms Sterna dougallii breeding on Aride Island (Seychelles), Indian Ocean, were studied in 1997 and 1998. I investigated to what extent two patterns, common in a range of species, were followed by tropical Roseate Terns: (a) seasonal decrease in clutch size, egg size and breeding success and (b) an increase in breeding success with increasing egg weight. In 1997 (a poor year), the earliest nesting birds laid significantly smaller eggs, and chicks were lighter at hatching than those of peak nesting birds. The mean clutch size, of 1.04 eggs, showed no seasonal variation and no 'b'-eggs hatched. In 1998 (a good year) the earliest nesting birds laid eggs of similar size and their chicks were of similar weight to those of peak nesting birds. Mean clutch size, of 1.25 eggs, increased significantly through the season and about 60% of the 'b'-eggs hatched. In 1997, hatching success was 57% whereas in 1998 it was 80%. In both years, breeding success declined significantly through the season. The fact that the earliest breeding birds laid smaller eggs in a poor year and smaller clutches in a good year is in marked contrast to a range of other species, and to temperate-nesting Roseate Terns. Egg volume explained about half of the variance in hatchling mass in both years, but only 15% of the variation in linear growth rate. Hatching date was the only variable with a significant effect on fledging success. Roseate Terns on Aride seemed to sacrifice egg size and clutch size for earliness of laying. Presumably it is a strategy of older birds to lay as early as possible and may be regarded as a response of tropical Roseate Terns to breeding under relatively poor, and seasonally declining, food conditions.     

FACTORS AFFECTING BREEDING OF RAZORBILLS ALCA TORDA ON SKOKHOLM

A study of the breeding biology of the Razorbill was carried out on Skokholm (South Wales) during 1971-73. Birds ringed or colour ringed before the study began provided additional information upon the effects of age on breeding. Mean laying date was delayed in 1972, compared with 1971; the effect is attributed chiefly to stormy weather which upset colony attendance. Eggs were also smaller in 1972. A seasonal decline in egg size (volume) was noted in all three years, attributed mainly to the later laying of young birds. Egg size increased with age, at least up to the fifteenth year. Eggs lost totalled 30% of those laid; 73% of this total was due to predation by Herring Gulls and of Jackdaws. Most losses (45%) occurred during the first 10 days after laying. Of lost eggs, 25% were replaced, usually 14 days after the loss of the original; only eggs laid and lost early in the season could be replaced. Only 7% of the chicks which hatched failed to fledge. Most (62.5%) chick losses occurred in the first week of nestling life, when chick weight was related to egg size. Afterwards, both growth rate and fledging weight were independent of egg size. The chicks fledging early in the season were heavier than later chicks. Failure to fledge was mainly due to a breakdown in behaviour between parent and young, rather than to predation. Breeding success was highest for birds breeding early in the season, most of which were older, more experienced breeders. These laid early enough to replace an egg if it was lost; they produced large eggs, and their chicks were therefore both heavier than average during the critical first 7–10 days of life, and fledged at a high weight. Thus experience accumulated with age, and the ability to lay early in the season are important for successful breeding in the Razorbill.     

Breeding biology of the thin-billed prion<Emphasis Type="Italic"> Pachyptila belcheri</Emphasis> at New Island,Falkland Islands: egg desertion,breeding success and chick provisioning in the poor season 2002/2003

We present data on breeding success, chick growth and chick feeding in thin-billed prions, Pachyptila belcheri, at New Island, Falkland Islands, in the breeding season 2002/2003. As in many populations of seabirds in the region, the overall breeding success was very low. This was mainly caused by low rate of observed burrow occupancy (60%) and hatching (57%) of thin-billed prions, while chick survival was closer to normal. Sixty-eight percent of the chicks survived to fledging. In total, a chick was successfully reared in 23% of the nests or from 38% of recorded eggs. The failed eggs were found to be incubated for 30 days, on average. The time of egg desertion coincided with the time of desertion of other seabirds at New Island, with a period of high sea-surface temperatures and low catch rates by the commercial fisheries. We describe chick growth and use repeated weighings, corrected for metabolic loss, to estimate meal sizes. Chicks were fed a mean 39.2 g in 77% of the nights. We discuss possible reasons for the observed extremely low hatching success, and compare with the breeding success of other seabirds at the Falkland Islands.     

Effects of experimental calcium availability,egg parameters and laying order on Great Tit Parus major eggshell pigmentation patterns

Many bird species lay eggs speckled with protoporphyrin‐based spots, however, for most of them the function of eggshell spotting is unknown. A plausible hypothesis is that protoporphyrin might have a structural function in strengthening the eggshell and is therefore deposited when calcium is scarce. In this study, we experimentally provided Great Tit Parus major females with supplemental calcium to examine its effect on the protoporphyrin‐based maculation of their eggs. In addition, we studied variation in eggshell pigmentation patterns in relation to other egg parameters and laying order. Calcium‐supplemented females laid larger eggs but shell thickness was not significantly affected by the treatment. Calcium supplementation may reduce the time and energy females devote to searching for calcium‐rich material, so that they can collect more nutrients and so lay larger eggs. Furthermore, pigment darkness was associated with egg volume and shape, which suggests that female quality and environmental food availability may also influence the shell pigmentation pattern. Within clutches, later‐laid eggs had larger and darker spots that were distributed more unevenly on the shell surface. This within‐clutch pattern could be explained by the increase in egg volume and egg shape and a decline in shell thickness with egg‐laying order, which characteristics were all related to shell‐spotting pattern. Eggs with a coronal ring had thinner shells, but pigment intensity and spot size were not related to shell thickness. Thus, our results suggest that concentrated spotting distribution may have a mechanical function, supporting the structural‐function hypothesis.     

CLUTCH SIZE, EGG SIZE, HATCH WEIGHT AND LAYING DATE IN RELATION TO EARLY MORTALITY IN RED GROUSE LAGOPUS LAGOPUS SCOTICUS CHICKS

Clutches of Red Grouse eggs were collected from the wild and subsequent hatching and rearing done in standard conditions in captivity. Variations in chick survival from one clutch to another in the same year were related to differences in hatch weight. Hatch weight was determined only partly by egg size. Weight loss between laying and hatching was related to survival independently of egg size. Variation in this weight loss obscured any simple relationship between egg size and survival, except in eggs laid by captive hens. Intrinsic differences amongst hens caused some variations in laying date, egg size, hatch weight and chick survival. Variations in egg size and hatch weight accounted for less than half the variation in survival; other unmeasured intrinsic factors were also important. Big clutches hatched earlier than small ones. The commonest clutches were of seven and eight eggs, with six and nine frequent. Very big clutches of ten or more eggs were infrequent and chicks from them sometimes survived worse than from smaller clutches. As in other species, the commonest clutch sizes were not the most productive. There was no simple relationship between egg size and clutch size.     

Adverse effects of instrumentation in incubating Adélie penguins (Pygoscelis adeliae)

The use of data-loggers has permitted to explore the biology of free-ranging animals. However, this method has also been reported to reduce reproductive success while the reasons of this deleterious effect remain poorly documented. In this study, we aimed to identify critical periods of the breeding cycle of Adélie penguins (Pygoscelis adeliae) when the reproductive success may decrease because of instrumentation. For this purpose, we monitored 40 pairs, where one parent was instrumented before egg laying and 30 pairs without devices (controls). These pairs were followed at least during the incubation period but the majority was monitored during the entire breeding season. Reproductive success was affected in pairs where males were instrumented. This was not due to extra chick mortality during chick rearing but to a significantly lower hatching success. Moreover, the use of artificial eggs recording incubation temperatures and egg rotation indicated that in instrumented incubating males, eggs spent as much time at optimal incubation temperatures as control eggs but were rotated at a higher frequency. In Adélie penguins, males initiate incubation and it has been established that the early stage of incubation is one of the most critical periods for embryonic development. The low hatching rate observed in instrumented males was associated with a higher egg rotation rate, perhaps as a stress response to the presence of the instrument. Even though the causal effects remain unclear, instrumentation severely affected hatching success. For these reasons, we recommend equipping birds after the early incubation.     

Soil pH influences embryonic survival in Pseudophryne bibronii (Anura: Myobatrachidae)

Abstract: There has been limited research examining the role that terrestrial habitat characteristics play in influencing persistence of amphibian populations. In this study we investigated the influence of a terrestrial habitat attribute on the distribution of the terrestrial egg‐laying toadlet, Pseudophryne bibronii. Eggs of this species are deposited in depressions, or under leaf litter, and develop to a stage where they can hatch to free swimming tadpoles when water covers breeding sites or embryos are washed into water. Because rainfall can be intermittent, eggs may sit for extended periods in terrestrial nests before sufficient rainfall initiates hatching. Appropriate egg‐laying sites must be chosen by both males and females to ensure embryos survive these periods. A study of 20 sites found that soil pH at sites where P. bibronii were recorded as present was significantly lower than pH at sites where P. bibronii were recorded as absent. To determine whether soil pH influenced the hatching success in P. bibronii, experiments were conducted in which batches of eggs were translocated to local areas with different soil pH. Survival rate of eggs was significantly influenced by relatively small changes in pH, with hatching success higher at lower pH. In a laboratory trial survival of eggs raised on sterilized soil was not affected by soil pH. Fungal infection of eggs was observed in the field and laboratory suggesting that hatching success might be affected via a complex interaction between soil pH, fungi and other soil biota. Choice trials using P. bibronii metamorphs indicated that individuals were capable of distinguishing between small differences in pH. Therefore, distribution of P. bibronii may be influenced by either differential mortality of embryos, or habitat choice by post metamorphic individuals, and further experiments are required to determine the relative importance of these factors.