A molecular genetic analysis of the communal nesting of the ostrich (Struthio camelus)

The ostrich breeding system is complex and unique; communal clutches are laid by several females, although only one female, the major female, and the resident territorial male provide parental care. More eggs are laid in the nest than can be incubated and the major female ejects surplus eggs from the incubated central clutch. Microsatellite markers were used to analyse the parentage of communal nests in Nairobi National Park. This revealed that major females contributed a disproportionate number of fertile eggs to the central, incubated clutch and that multiple paternity and maternity within a nest were common; 68.9% of all incubated eggs on a nest were not parented by both the resident territorial male and the major female of that nest. All the males fertilized eggs on the clutches of neighbouring males. Unexpectedly, every major female with her own nest was also simultaneously a minor female with incubated eggs on neighbouring clutches. The relatedness between females laying in the same nest was not significantly different from the population average and significantly less than that between chicks hatched from the same nest.     

NESTING OF THE PURPLE-THROATED CARIB HUMMINGBIRD

We present data on certain parts of the nesting biology of the Purple-throated Carib Humming- bird Eulampis jugularis on the island of Dominica, British West Indies. We watched two nests with eggs and young and a single nest under construction. Incubation was in short periods averaging about six minutes. Females at both nests with eggs continued adding material to the nest until the end of incubation. We suggest that this common practice among hummingbirds may insure that a limited amount of energy at the time of initial nest-building and egg-production is optimally apportioned between the two activities. Brooding ceased in one nest when the young were about 13 days old. Feeding rates stayed relatively constant at one to two per hour throughout the nearly complete nestling period in one nest. Average time per feeding declined, apparently as the female-young interaction became more efficient with maturation of the young. Nesting females foraged on both insects and nectar. We could not be sure what they were feeding the young. Defence of the nest varied with the position of the female and the type of intruder. The aggressive behaviour associated with defence varied according to the size and type of intruder. We concluded that for the one nest of Eulampis for which we had the most complete data, had there been three young, the female would have been unable to provide sufficient food to nourish them. However, the universal clutch size of two and nearly universal promiscuity in humming- birds is strong evidence that factors other than the ability of adults to feed more than two young are important in determining clutch size.     

Intraspecific nest parasitism in the European starling Sturnus vulgaris

Biochemical genetic markers were used along with conventional methods (abnormal laying sequence/clutch size, unusual egg shape/pigmentation) to identify intraspecific nest parasitism at two British nestbox colonies of the European starling. Between 11 and 37% of first clutches were parasitized during 1977–1979. Parasitic females probably comprised all of the following categories: (1) paired females contesting a nestbox occupied by another pair; (2) previously paired females who had laid a clutch but had been unsuccessful; (3) unpaired females who had copulated with males that already had a mate and nest site; and (4) ‘professional’ nest parasites who distributed at lest some of their eggs in one or more nests other than their own. Although parasitized nests had higher clutch sizes, parasitism led to fewer host young fledging per egg laid, mainly through the eviction of eggs and subsequent nest desertion. Number of parasitic young fledged per egg laid was highest when eggs were laid synchronously with the host, when host clutches were larger, or a smaller number of parasite eggs were added to a nest, thus favouring parasites that distribute their eggs amongst a number of nests. A greater pressure on nest sites may have accounted for the higher levels of parasitism at the Aberdeen colony and for the greater number of parasite eggs laid in a nest. Although most parasitic female starlings appeared to be much less successful than non-parasitic ones, nest parasitism in the starling might evolve directly when one or more of the following advantages are present. (1) There are no constraints on the number of eggs a female may lay but there are constraints on the number of young she may feed adequately. (2) Female survival is increased by having fewer or no eggs/young to care for. (3) Current feeding conditions favour the survival of more young than would be produced by the most common clutch size. Intraspecific nest parasitism is considered to be a first stage in the evolution of interspecific nest parasitism.     

Intensive genetic assessment of the mating system and reproductive success in a semi-closed population of the mottled sculpin,Cottus bairdi

Most genetic surveys of parentage in nature sample only a small fraction of the breeding population. Here we apply microsatellite markers to deduce the genetic mating system and assess the reproductive success of females and males in an extensively collected, semi-closed stream population of the mottled sculpin fish, Cottus bairdi. In this species, males guard nest rocks where females deposit the eggs for fertilization. The potential exists for both males and females to mate with multiple partners and for males to provide parental care to genetically unrelated offspring. Four hundred and fifty-five adults and subadults, as well as 1,259 offspring from 23 nests, were genotyped at five polymorphic microsatellite loci. Multilocus maternal genotypes, deduced via genetic analyses of embryos, were reconstructed for more than 90% of the analysed nests, thus allowing both male and female reproductive success to be estimated accurately. There was no genetic evidence for cuckoldry, but one nest probably represents a takeover event. Successful males spawned with a mean of 2.8 partners, whereas each female apparently deposited her entire clutch of eggs in a single nest (mean fecundity = 66 eggs/female). On average, genetically deduced sires and dams were captured 1.6 and 9.3 metres from their respective nests, indicating little movement by breeders during the spawning season. Based on a 'genetic mark-recapture' estimate, the total number of potentially breeding adults (c. 570) was an order-of-magnitude larger than genetically based estimates of the effective number of breeders (c. 54). In addition, significantly fewer eggs per female were deposited in single than in multidam nests. Not only were perceived high-quality males spawning with multiple partners, but they were receiving more eggs from each female.     

Habitat of the Golden Nightjar Caprimulgus eximius

The Ostrich communal breeding system involves several females laying in a single nest. Only the ‘major’ female and the territorial male, however, provide parental care from incubation to fledging of chicks. Eggs are turned and displaced frequently upon the onset of incubation, and the major female evicts excess eggs out of the nest when the number of eggs is above a specific threshold level. A previous study indicated that the major female ostrich recognises her own eggs and selectively evicts eggs of minor females based on size, shape and shell texture. Our aim was to investigate if accepted and ejected eggs differ in colour characteristics. We quantified colour by measuring egg reflectance spectra, which were subsequently analysed using a visual model approach. Within clutches, there were no significant differences in colour between accepted and ejected eggs. These results suggest that female ostriches do not discriminate against foreign eggs based on deviations in colour.     

Don'T put all your eggs in one nest: spread them and cut time at risk

Abstract In many egg-laying animals, some females spread their clutch among several nests. The fitness effects of this reproductive tactic are obscure. Using mathematical modeling and field observations, we analyze an unexplored benefit of egg spreading in brood parasitic and other breeding systems: reduced time at risk for offspring. If a clutch takes many days to lay until incubation and embryo development starts after the last egg, by spreading her eggs a parasitic female can reduce offspring time in the vulnerable nest at risk of predation or other destruction. The model suggests that she can achieve much of this benefit by spreading her eggs among a few nests, even if her total clutch is large. Field data from goldeneye ducks Bucephala clangula show that egg spreading enables a fecund female to lay a clutch that is much larger than average without increasing offspring time at risk in a nest. This advantage increases with female condition (fecundity) and can markedly raise female reproductive success. These results help explain the puzzle of nesting parasites in some precocial birds, which lay eggs in the nests of other females before laying eggs in their own nest. Risk reduction by egg spreading may also play a role in the evolution of other breeding systems and taxa-for instance, polyandry with male parental care in some birds and fishes.     

ON THE LIFE-EXPECTANCY OF THE MATOPOS BLACK EAGLES

Oatley, T. B. 1982. The Starred Robin in Natal, Part 3: Breeding, populations and plumages. Ostrich 53: 206–221 The female Starred Robin Pogonocichla stellata constructs a domed nest of moss and dead leaves usually on sloping ground and well concealed in the herb layer. The normal clutch is three eggs laid on consecutive days. Incubation usually starts with the laying of the third egg. The mean size of 138 eggs was 22 x 16 mm. The female incubates the eggs for 16 to 18 days and intermittently broods the young for the fist five of the average 14-day nestling period. Both sexes feed the young from the time of hatching and parental care lasts for some 42 days after leaving the nest. Eggs are laid from October to December with 63% of clutches started in November. Data on sex ratios indicate a surplus of adult males in the population and annual survival rates are estimated at 0,84 for males and 0,76 for females. 51% of eggs laid in 60 nests give rise to fledged young. About 21.3% of eggs laid produce adults. The level of brood parasitism by cuckoos is relatively low. Most adult mortality occurs outside of the breeding seasons. Chilling and overnight starvation from January to March when incidence of late afternoon thunderstorms is highMaycause significant mortality. The subadult plumage appears to confer crypsis and enable the immature bird to reside in adult territories without harassment. AdultsMaybenefit through an effective reduction in competitive stress.     

THE TIMING OF BIRDS' BREEDING SEASONS

Examination of survival rdtes of nestlings and fledglings of some species show that there is a strong tendency for those young which are hatched earliest in the season to have the greatest chance of surviving to breed. Since natural selection so strongly favours parents who leave many surviving young, the question arises as to why other birds breed later than the date at which they could most successfully raise their young.
It is suggested that the food supply for the breeding females immediately prior to the breeding season may limit their ability to form eggs and the females may thus not be able to lay at the time which would result in young being in the nest at the best time for raising them, but as soon after this time as the female is able to produce her eggs. Not all species are likely to be prevented, by food shortage, from breeding at the best time for raising young and the groups of birds most likely to be affected are discussed.     

The importance of body reserves for successful reproduction in the Tawny owl (Strix aluco)

One-quarter of Tawny owl nests fail to hatch young, mainly because the eggs are chilled and/or deserted. In 1973–74 automatic photography was employed at four nests near Oxford to relate the incubation behaviour of females to the ration of prey supplied to them by their mates. The eggs did not hatch in two nests and young fledged from only one of the others. Females were less attentive at the nests which failed during incubation and on average received less prey, but even at successful nests there were some nights when the female was supplied with less than her estimated daily food requirement. Female Tawny owls accumulate large reserves of fat and protein before laying. These buffer against any temporary inability of the male to provide sufficient food during incubation, and enable the female to stay on the nest rather than hunt for herself and risk the eggs becoming chilled. When prey are scarce, many females do not lay at all, and the ultimate factor determining whether breeding takes place may be the female's ability to acquire body reserves sufficient to provide a chance of breeding successfully.     

CLUTCH CHARACTERISTICS AND EGG DISCRIMINATIVE ABILITY OF THE AFRICAN VILLAGE WEAVERBIRD PLOCEUS CUCULLATUS

Over a three-year period, 917 eggs from 27 females were collected from a captive colony of African Village Weaverbirds Ploceus c. cucullatus. A study was made of egg-laying and incubation behaviour, clutch characteristics and egg recognition.
Fifteen yearling females laid their first clutches at a mean age of 348 days after hatching. The mean clutch-size was 2.26 in adults and 1.68 in yearlings. The mean clutch replacement interval was 6.6 days in adults and 7.4 days in yearlings with an absolute minimum of 4 days. Eggs were laid at intervals of from 24 to 26 hours beginning usually 2–3 hours after dawn.
The eggs laid by this species vary in ground colour and pattern of spotting between different females, but egg pigmentation is constant for each individual bird. The results of 322 egg-replacement tests showed that an individual female could recognise her own egg type and would eject from the nest eggs differing markedly from her own. The incidence of rejection was proportional the degree of difference between the eggs. The possible implications for parasitism by the Didric Cuckoo Chrysococcyx cuprius are discussed.     

Egg speckling patterns do not advertise offspring quality or influence male provisioning in great tits

Many passerine birds lay white eggs with reddish brown speckles produced by protoporphyrin pigment. However, the function of these spots is contested. Recently, the sexually selected eggshell coloration (SSEC) hypothesis proposed that eggshell color is a sexually selected signal through which a female advertises her quality (and hence the potential quality of her future young) to her male partner, thereby encouraging him to contribute more to breeding attempts. We performed a test of the SSEC hypothesis in a common passerine, the great tit Parus major. We used a double cross-fostering design to determine whether males change their provisioning behavior based on eggshell patterns they observe at the nest. We also tested the assumption that egg patterning reflects female and/or offspring quality. Because birds differ from humans in their color and pattern perception, we used digital photography and models of bird vision to quantify egg patterns objectively. Neither male provisioning nor chick growth was related to the pattern of eggs males observed during incubation. Although heavy females laid paler, less speckled eggs, these eggs did not produce chicks that grew faster. Therefore, we conclude that the SSEC hypothesis is an unlikely explanation for the evolution of egg speckling in great tits.     

Mate Choice and Mating Pattern in a Stream Goby of the Genus Rhinogobius

The mate choice and mating pattern of a benthic goby Rhinogobius sp. CB (cross band type) were investigated in the Kamo River, Shikoku, Japan. During the breeding season, gravid females assumed a nuptial color and either males or females initiated a courtship display. Males preferentially courted a female of similar size to lead her to his nest, whereas females courted more frequently when they encountered a large male. Eggs in any one nest were always at the same developmental stage. Sampling data of nesting males and females indicated that, in more than half the nests, males gathered more than one female before spawning. In some nests with eggs, two or three females had spent ovaries, indicating that the eggs were laid by multiple females within a short span of time. However, a comparison between the total number of eggs which females would spawn in one nest and the number of eggs actually deposited suggested that eggs were contributed by one female in most nests. This low level of polygyny in spite of multiple female availability is attributed to a limited available spawning area of the nest.     

OBSERVATIONS AT A NEST OF THE CUCKOO-ROLLER LEPTOSOMUS DISCOLOR

A nest-cavity with two nestlings of Leptosomus discolor, found in the Comoro Islands in October 1965, are described. This is apparently the first time that nesting has been observed. The nest was in a natural cavity in a tree growing in light secondary forest. Both nestlings still had traces of their original white down, even though they were nearly fully-feathered. Apart from two thick tufts of white down on the hind-crown, the plumage appeared very like that of the adult male. Fragments of egg-shell were found in the nest. They suggest that the original eggs were rather rounded, of a pale unmarked creamy-buff, slightly glossed, measuring about 46 ± 5 ± 37 ± 5 mm. During six hours observation at the nest the birds made five visits and brought six chameleons (no other food was seen). The female fed the young, but the male accompanied her. She did not enter the nest, except on one occasion. Details of this visit are given in full, being particularly remarkable for the tameness of the female. The threat-display of the young is described and possible predators mentioned. Several calls are described, some apparently for the first time. It seems likely that most prey is caught above ground-level. The evidence suggests that the birds are monogamous, not polyandrous as has been suggested.     

4. A FIELD NATURALIST'S PEREGRINATIONS. BIRD NOTES FROM A NORTHERN SECTOR OF SOUTHERN RHODESIA—Part III

Boyer, H. J. 1988. Breeding biology of the Dune Lark. Ostrich 59:30-37.

The peak of the breeding season of the Dune Lark Mirafra erythrochlamys occurred in January and February and was not dependent on rainfall. Most nests were domed, although one undomed nest was recorded. Ninety-one percent of clutches were of two eggs (mean = 1,9; range 1–2; n = 11). The eggs are described and measurements given. Incubation, by the female only, began with the laying of the second egg, and hatching occurred after 13–14 days. Growth and development of nestlings are described. The young left the nest after 12–14 days, and post-nestling parental care lasted for approximately one month. Sixty-one percent of eggs hatched. and 28% produced young which successfully left the nest. Most losses of eggs and young were the result of predation.     

Age-specific reproductive performance of Black Grouse Tetrao tetrix females

As part of a demographic study of Black Grouse in the southern French Alps, we estimated variations in reproductive parameters in relation to age of females. Both yearlings and adults initiated a clutch, but adults raised about eight times more young (yearlings 0.25 chicks/females, adults 1.85 chicks/female). Yearlings laid significantly fewer eggs and initiated incubation later than older females. Success of nests did not differ between the two age classes, but yearlings tended to re-nest less frequently and exhibited higher chick loss than older females. The lower reproductive success of yearlings was primarily due to their lower ability to raise young. At nest sites, nest concealment, as well as vertical and horizontal structure and density of the vegetation, did not differ between yearling and older females, which is consistent with the similarity in nesting success in the two age classes. Results support the hypothesis that the extent of the difference in number of young raised by yearling and older females increases with predation pressure.     

The nesting biology and population dynamics of the Seychelles potter wasp Eumenes alluaudi Perez

Abstract. 1. The nesting biology of the solitary potter wasp Eumenes alluaudi was studied on Cousin Island, Seychelles.
2. Although the rainy season was from October to April there was no indication of strong seasonality in the wasps' nesting.
3. Females tended to nest close to where other females were nesting.
4. The mean number of cells per nest was 3.71, the mean number of nests made per female 135, and the percentage of cells from which adults emerged 65.87; thus the mean number of adult wasps emerging from the nest(s) of each breeding female was 3.29.
5. Male-producing eggs were laid before female-producing eggs and the estimated sex ratio at emergence was, at 1:2.52, female biassed. It is possible that inbreeding occurred.
6. Daily mortality of nesting females was estimated as 0.088.
7. The mean interval between a female's emergence and her starting to nest was 19.7 days.
8. Marking showed that only 26.7 ± 6.3% of females emerging from cells in the study area returned to breed there. Since the number of emerging daughters per breeding female was only 5.01 times 0.66 times 0.72 = 2.36 (fecundity x proportion emerging x proportion of females emerging), the number of returning females would be only 236 times 0.267 = 0.63, and hence, in order to maintain numbers over many generations, 037 females must have been immigrants.     

Why do snow geese adopt eggs?

Nesting female lesser snow geese (Anser caerulescens caerulescens)usually adopt eggs that are laid adjacent to their nests bypotential intraspecific nest parasites. The host female rollsthe parasite’s egg up into the nest, using the same behaviorpatterns used to retrieve her own eggs if they are displacedfrom the nest. The reproductive consequences of adopting eggsare unclear. We consider three selective scenarios that mightmaintain adoption behavior in geese: (1) egg adoption is ofno reproductive consequence to the host; (2) egg adoption augmentshost reproductive success relative to that of unparasitizednests; and (3) egg adoption is making the best of a bad situation,once a female’s options are constrained by the presenceof an egg adjacent to the nest; we also consider (4) the possibilitythat adoption, if not concordant with the selective regime,is maladaptive. Nest parasitism is costly to the host, makinghypotheses 1 and 2 unlikely. However, adopting eggs significantlydecreases the risk of total nest failure during laying, morethan offsetting other probable host costs. This is consistentwith hypothesis 3. Experiments show that geese have limitedabilities to retrieve eggs, which accounts for most cases ofnonadoption of nearby eggs. We conclude that adoption of eggsis an adaptive trait, a form of nest protection. Adopting eggsis the best option within the species’ repertoire to thethreat to nest survival created when a parasite lays an eggnext to the nest. [Behav Ecol 1991;2:181-187]     

Mate preferences of female mottled sculpins, Cottus bairdi

Experimental manipulation of breeding site quality did not alter the mate preference of female mottled sculpins (Cottus bairdi). Females of this species appear to choose mates on the basis of male size. By choosing a larger male, a female increases the probability that some of her eggs will hatch because large males are unlikely to abandon their nest sites.     

An empirical test of the `predictability' hypothesis for the evolution of viviparity in reptiles

Abstract Viviparity (live‐bearing) has evolved from oviparity (egg‐laying) >100 times in reptile phylogeny, but the selective forces responsible remain unclear. Tinkle & Gibbons (1977) proposed that prolonged uterine retention of eggs (leading ultimately to viviparity) is favoured by natural selection when it allows the reproducing female to better predict the incubation conditions that will occur in alternative potential nest‐sites, and hence select the optimal site in which to deposit her eggs. This ingenious hypothesis has never been tested empirically. Over a 7‐year period, I monitored temperatures inside 124 natural nests of egg‐laying scincid lizards at three different elevations in the Brindabella Range of south‐eastern Australia. As a measure of thermal predictability, I used correlation coefficients from comparisons of temperatures early vs. later in incubation among nests within each site. Both the mean and standard deviation of nest temperatures were examined in this way for each week through incubation. I performed these calculations under two models: one where the female assesses nest temperatures at the time of oviposition only, and one where she monitors temperatures constantly from the usual oviposition date until the actual time of laying. These analyses falsified two major assumptions of the ‘predictability’ hypothesis. First, nest temperatures at higher elevations were no less predictable than were those at lower elevations; instead, predictability was high in all situations. Secondly, a longer delay before oviposition decreased rather than increased the predictability of thermal conditions during subsequent incubation. I conclude that critical assumptions of the ‘predictability’ hypothesis are not supported in this study system.