Intraspecific nest parasitism in the Spotless Starling Sturnus unicolor

Intraspecific nest parasitism in two colonies of Spotless Starling Sturnus unicolor breeding in nestboxes was studied in central Spain from 1991 to 1994. Nests were monitored regularly and three criteria were used to detect nest parasitism: the appearance of more than one egg per day during the laying period of the host; the appearance of an egg after the start of incubation; eggs with unusual shape or pigmentation. The proportion of parasitized nests in first clutches (37%) was twice that of intermediate (19%) or second (20%) clutches in colony B, whereas parasitism occurred in first (35%) and intermediate (12%) but not in second clutches in colony A. Most clutches (52–70%) were parasitized during the host's laying period and received one parasitic egg. In 10% of the parasitized clutches in colony B, one of the host's eggs disappeared on the day the parasitic egg was added, suggesting that the parasitic female removed this egg. Although parasitism increased clutch size significantly, it led to a decrease in host breeding success, mainly through the removal of eggs and the loss of host nestlings and the survival of parasitic chicks. Observations suggested that parasitic females were young individuals without their own nests and/or those whose breeding attempt had been disrupted while laying in their own nest.     

Effect of brood size and hatching sequence on prefledging mortality of Sandwich terns: why lay two eggs?

The mortality of Sandwich tern Sterna sandvicensis chicks held in enclosures was studied in colonies on Griend, in the Dutch Wadden Sea, from 1992 to 1999, and on Hirsholm, in the Danish Kattegat, in 1997. Survival of chicks until fledging was 73% for chicks hatching from first-laid eggs or single-egg clutches and 59–64% for partially hatched two-egg clutches, whereas 6% of second hatchlings survived until fledging. Less than 2% of all two-chick broods actually fledged two chicks. Because 18% of the two-egg clutches only hatched one egg, 7% of fledglings of two-egg clutches originated from a second-laid egg. In nests where both eggs hatched, the number of chicks was usually reduced soon after hatching. Within five days of hatching more than 50% of the second hatchlings died of starvation or were preyed upon. It seems that overproduction commonly occurs in Sandwich terns and that investment in a surplus egg mainly serves as an insurance mechanism. On Griend and Hirsholm, chick productivity of two-egg clutches was somewhat higher than for one-egg clutches. Undernourishment was an important cause of death, either directly by starvation or by selective predation of chicks in poor condition. This, in combination with earlier, studies suggests that Sandwich tern parents on Griend are exposed to severe food stress.     

Functional significance of variation in egg-yolk androgens in the American coot

Maternally derived hormones in cleidoic eggs have been implicated in mediating growth, behavior, and social interactions among offspring. Given these widespread and significant effects, hormonal investments have the potential to greatly influence fitness of offspring. Intraspecific variation can exist at three levels (within individual eggs, among eggs within clutches, and among eggs from different females), each of which has different implications for offspring. We characterized all three levels of variation in maternally derived androgens (testosterone and androstenedione) present in yolks of American coot eggs. We found no variation in testosterone levels within eggs which suggests that embryos are exposed to constant androgen levels during development, and that field-based yolk biopsies are an appropriate way to sample eggs for this species. Within clutches, early-laid eggs had higher androgen levels than late-laid eggs, and this pattern may exacerbate negative effects of hatching asynchrony on chicks from late-hatching eggs if androgens provide chicks with a behavioral or growth advantage over chicks from eggs with lower androgen levels. American coots lay large clutches, and unequal resource allocation among offspring may be the optimal strategy for females with access to limited resources. Most of the variation in androgen levels occurred among eggs from different females. Females nesting on ponds with two other pairs laid eggs with significantly higher androgen levels than females living on ponds with fewer pairs. This suggests that increased territory defense behaviors influence the levels of androgens allocated to eggs and may be one mechanism underlying density-dependent effects on reproduction.     

Clutch size limitation in waders: experimental test in redshank Tringa totanus

Several hypotheses have been raised to explain the upper limit of clutch size at four eggs in waders (suborder Charadrii), which may play an important role in the evolution of the variety of mating and parental care systems in this group. Experimental tests of the hypotheses have produced conflicting results. It was recently suggested that the combined effects of several incubation costs of a larger clutch suffice to limit its size to four eggs in this group. Here we test the incubation-limitation hypothesis in a field experiment, in redshank Tringa totanus. We created five-egg clutches by adding one egg from another nest to a just completed four-egg clutch. Four-egg control clutches were created by replacing one of the eggs by an egg from another nest. All egg removals, additions and replacements were done before incubation started. Incubation time in five-egg clutches increased by 1 day to 24.3ǂ.23 days, compared to 23.3ǂ.32 days in four-egg clutches. Egg hatchability and nest predation rates did not differ significantly between treatments. On average five-egg clutches produced one extra chick at hatching (4.5ǂ.26 chicks) compared to four-egg clutches (3.5ǂ.27 chicks). Also when several additional costs from incubating enlarged clutches are added, redshanks by laying a fifth egg would on average increase their reproductive success at hatching by an estimated 22%. The incubation-limitation hypothesis therefore is clearly rejected in this species. Possible mechanisms behind the four-egg clutch limit in waders and ways of testing the alternatives are discussed.     

Intraspecific nest parasitism in the grey starling (Sturnus cineraceus)

We studied intraspecific nest parasitism in the grey starling (Sturnus cineraceus) in 1992 and 1993. We used three criteria to detect nest parasitism: (i) the appearance of more than one egg per day while the host was laying; (ii) the appearance of extra eggs after the host completed its clutch; and (iii) the appearance of eggs which were of a different shape, size and color to other eggs in the clutch. There were 290 nests (157 nests in 1992; 133 nests in 1993) in which the clutch was completed early (clutches initiated before May 10). Twenty-nine (1992) and 32 (1993) nests contained at least one parasitic egg. Parasitic eggs hatched if they were laid during the laying period and early in the incubation period of their host, and a few of them fledged. Fledging success of parasitic eggs was not different from that of eggs in non-parasitized nests if parasitic eggs were laid during the host's laying period. However, fledging success of all parasitic eggs was fewer than that of eggs in non-parasitized nests. By comparison, fledging success of parasitized nests was not a great as that of non-parasitized nests.     

Rates and consequences of relaying in little auks Alle alle breeding in the High Arctic an experimental study with egg removal

Most seabirds have a small clutch size. Thus, replacement of a clutch after loss can make important contributions to an individual’s lifetime reproductive success. However, in the condition of short polar summer, relaying propensity may be time‐constrained. In this study, we investigated rates and consequences of relaying in a small High Arctic seabird, the little auk Alle alle. We performed an experiment in which we removed the single egg from 20 nests of early‐laying breeders. We measured relaying rates, and compared chick body mass and breeding success between the experimental and control nests. Despite the narrow window of the Arctic summer and the closely synchronized breeding, 75% of females produced a replacement egg just 2.7% smaller in volume than the first egg. This indicates that in little auks, the demographic effects of disruptions to breeding attempts (by predators, adverse weather or human activity) may be mitigated to some extent by replacement clutches. However, peak body mass and fledging body mass were lower in the experimental than the control chicks. This effect was rather a consequence of late hatching – chicks from replacement clutches followed seasonal decline in peak body mass and fledging mass. Finally, breeding success and chick survival up to 20 d in the experimental nests were respectively 34 and 37% lower than in the control nests. Thus, the quality and post‐fledging survival of chicks from the replacement clutches were probably lower compared to the chicks hatched from the first‐laid eggs.     

Parental quality and egg size affect chick survival in a precocial bird, the lapwing Vanellus vanellus

Effects of egg size and parental quality on lapwing Vanellus vanellus chick survival were studied in southwestern Sweden over 6 years. Chicks from large eggs were heavier at hatching and survived significantly better than those from small eggs. To control for the confounding effect of parental quality on egg size and chick survival, we performed a cross-fostering experiment during 2 years, exchanging clutches between nests with large and small eggs. In control clutches, chicks from large eggs survived better than those from small eggs, but we found no significant difference in chick survival between exchanged clutches. Thus, egg size did not affect chick survival independently of parental quality. Fledging success increased with parental age and/or experience, and with female body mass. Hence, both egg size and parental quality affect chick survival in the lapwing. Received: 22 February 1996 / Accepted: 30 September 1996     

Conspecific nest parasitism in the Pied Avocet Recurvirostra avosetta

Evidence for the occurrence of conspecific nest parasitism (CNP) in Pied Avocets Recurvirostra avosetta is presented. Clutches of more than four eggs had obviously been produced by more than one female but were incubated by only one pair each. Minimum estimates for the frequencies of parasitized clutches and parasitic eggs were 3.3% and 1.3% respectively. CNP increased in frequency in colonies with higher nest densities. The frequency of CNP was unaffected by the rate of nest failures early in the season. On average, parasitic eggs were laid earlier in the season than the majority of non-parasitic eggs. Parasitic Avocets usually deposited their eggs during the laying period of host nests. Parasitized nests had significantly longer incubation periods than unparasitized nests. Hatching success in supernormal clutches was insignificantly reduced compared with four-egg clutches. The annual breeding success of individuals with parasitized clutches was considerably (but not significantly) higher than those of non-parasitized individuals. This was probably due to the fact that parasites chose to deposit their eggs in dense colonies whose members had significantly higher breeding success than the individuals in loose colonies. In colonies with a high rate of CNP, the frequency of clutches of more than five eggs increased. These clutches had little chance of survival.     

Intraclutch egg-size variation and offspring survival in the Kentish Plover Charadrius alexandrinus

We studied the consequences of intraclutch egg-size variation in Kentish Plovers Charadrius alexandrinus in southern Spain to test the hypothesis that females allocate resources preferentially to eggs with the greatest survival potential. Second eggs were larger and had a greater hatching success than the other eggs in a clutch. However, we did not find unequivocal support for the differential allocation hypothesis, because egg failures according to laying order were not due to the causes predicted by the hypothesis, and the change in egg-size with laying order was not consistent between successive clutches of renesting females. This suggests that nutrient availability during egg formation could act as a proximate factor affecting egg-size independently of laying order. Larger eggs produced heavier chicks and, within broods, heavier chicks were most likely to be recruited into the breeding population. By laying clutches with a larger mean egg volume in replacement clutches, females took longer to lay again after failure of the first clutch. Thus, opposing selective forces may act to increase and decrease egg volume. Although a trade-off between egg-size and clutch-size has not been found in precocial birds, our results suggest that there may be a trade-off between egg-size and fecundity, since an increase in the size of eggs within clutches may limit the time remaining within the season to lay second or replacement clutches.     

Breeding biology of the Redwing Francolin in the highland grasslands of Mpumalanga Province,South Africa

We studied the breeding biology of the Redwing Francolin, Francolinus levaillantii, in the highland grasslands of Mpumalanga Province, South Africa, from 1995–1996. The breeding season is from August to March. Clutches were incubated by hens only and all nests were located in rank grass close to surface water. Mean clutch size was 4.3 eggs (S.D. = 0.78, n = 10) and mean egg dimensions were 40.1 × 32.3 mm (S.D. = 1.07 and 0.81, n = 44). Hatching success was 83.7% and clutch survival rate to 22 days of incubation was 82.8%. A mean of 3 chicks was produced per clutch; observed mean production (counts of hens with chicks) was 2.6 chicks per brood (n = 24 clutches; 62 chicks). The hunting season for Redwing Francolin in Mpumalanga should be from 15 April to 15 July.     

The sight of an adult brood parasite near the nest is an insufficient cue for a honeyguide host to reject foreign eggs

Hosts of brood‐parasitic birds typically evolve anti‐parasitism defences, including mobbing of parasitic intruders at the nest and the ability to recognize and reject foreign eggs from their clutches. The Greater Honeyguide Indicator indicator is a virulent brood parasite that punctures host eggs and kills host young, and accordingly, a common host, the Little Bee‐eater Merops pusillus frequently rejects entire clutches that have been parasitized. We predicted that given the high costs of accidentally rejecting an entire clutch, and that the experimental addition of a foreign egg is insufficient to induce this defence, Bee‐eaters require the sight of an adult parasite near the nest as an additional cue for parasitism before they reject a clutch. We found that many Little Bee‐eater parents mobbed Greater Honeyguide dummies while ignoring barbet control dummies, showing that they recognized them as a threat. Surprisingly, however, neither a dummy Honeyguide nor the presence of a foreign egg, either separately or in combination, was sufficient to stimulate egg rejection.     

Effects of clutch size and egg-laying order on the breeding success in the Little Tern Sterna albifrons on the Nakdong Estuary, Republic of Korea

Survivorship of Little Tern Sterna albifrons eggs and chicks was followed on an islet in the Nakdong Estuary, Republic of Korea, in 1995 and 1996. Mean egg size and incubation period were significantly different between the 2 years. The maximum clutch size was three eggs, and the second egg in the clutch often hatched earlier than the first, while most of the third eggs hatched last. In 1996, when the fate of 249 eggs from 106 nests was followed for 40 days, hatching success, fledging success and breeding success were 77%, 40% and 31%, respectively. High mortality occurred in the early chick stage, mostly because of rain and predation by Weasels Mustela sibirica. The breeding success per egg was 14% in one-egg clutches, 28% in two-egg clutches and 34% in three-egg clutches. This difference was mainly attributed to the lower hatching success in the smaller clutches. In three-egg clutches, the third egg showed significantly lower breeding success than siblings. The main foods of the Little Tern were Tridentiger obscurus, Engraulis japonicus, Hyporhamphus intermedius, Acanthogobius flavimanus (all fish), Palaemon sp. and Crangon affinis (shrimps). The feeding frequency was, apparently, not affected by time of day and age of chicks but was probably influenced by weather conditions. Newly hatched chicks failed to eat 25% of the prey brought to them, although this decreased with the age of the chicks.     

Geographical variation in egg size dimorphism in rockhopper penguins

All crested penguins present a unique reversed hatching asynchrony: the larger second-laid egg (B-egg) hatches before the smaller first-laid egg (A-egg). Although both eggs often hatch, the A-chick generally dies of starvation within days after hatching. However, within rockhopper penguins, the population at the Falkland Islands is unique in that some birds manage to raise both chicks. Although it has been suggested that the egg size dimorphism between A- and B-eggs may explain how long both eggs and chicks survive, this hypothesis has never been explicitly tested. We expect that both eggs are retained longer in the less dimorphic clutches than in the more dimorphic ones. In this paper, we have compiled egg measurements for three rockhopper penguin species (Eudyptes chrysocome, E. filholi and E. moseleyi) in order to compare the intra-clutch egg size dimorphism among these species. Furthermore, we have collected new data to compare egg size dimorphism between two populations of E. chrysocome (Falkland Islands versus Staten Island). A-egg volumes are more variable between species and populations than B-egg volumes. E. chrysocome and especially the population from the Falkland Islands produces the largest A-eggs and the least dimorphic eggs. Nevertheless, as differences in A-egg volumes between species and between the populations of Falkland Islands and Staten Island are stronger and more significant than differences in egg dimorphism, we suggest that A-egg volume, more than egg dimorphism, could be one of the factors influencing the prevalence of twins. A large A-egg and/or reduced egg dimorphism is probably necessary to enable rockhopper penguins to raise two chicks, but other reasons may also be involved which enable them to keep both eggs and chicks.     

Captive breeding for reintroduction: influence of management practices and biological factors on survival of captive kaki (black stilt)

An important component of the restoration strategy for the critically endangered kaki or black stilt (Himantopus novaezelandiae) is captive breeding for release. Since 1981 1,879 eggs were collected from wild and captive pairs, with birds laying up to four clutches. Eggs were incubated artificially and most chicks reared by hand until released as juveniles (about 60 days) or sub‐adults (9–10 months). Because survival in captivity is a significant determinant of the number of birds available for release, we wished to identify sources of variation in mortality to assess potential impacts of management on productivity. Hatchability was 78% for captive‐laid eggs and 91% for wild‐laid eggs. Survival of hatched eggs was 82% by 10 months of age for both wild and captive birds. Most egg mortality occurred early in incubation and around hatching: the timing of mortality was unaffected by whether birds were captive or wild, hybrid or pure kaki, or when eggs were laid. Heavier hatchlings showed higher initial survival, as did chicks from wild parents. Hatchlings from fourth‐laid eggs showed lowest survival, even though hatchling mass tended to increase with hatch order. Survival of chicks subjected to major health interventions was 69% after 4 months. No differences in survival were found between different genders, hybrids and pure kaki, hand‐reared or parent‐reared birds, chicks hatching early or late in the season, different seasons, different‐sized groups of chicks, chicks reared in different brooders, juveniles kept in different aviaries, and chicks from subsequent clutches. Birds subjected to minor health interventions were equally likely to survive as healthy chicks (82%). Survival was high despite aggressive management (quadruple clutching and collecting late in the season). Differences between captive and wild birds suggest further improvements could be made to captive diet. Wide variation in hatchability between parent pairs substantiates the practice of breaking up poorly performing pairs. Zoo Biol 0:1–16, 2005. © 2005 Wiley‐Liss, Inc.     

Influences of adult age and experience, nest location, clutch size and laying sequence on the breeding success of the Great skua Catharacta skua

In 881 nesting attempts by Great skuas on Foula during 1975 and 1976, 1.24 chicks were fledged per pair. Addled eggs and egg predation were the main causes of losses. Eggs rolled out of the nest were not retrieved. Almost all chicks which hatched also fledged. Young or inexperienced breeders were almost as successful as older or experienced pairs. Birds producing single egg clutches and addled eggs usually also showed low aggression and held small territories. Egg predation was greatest at high nest density, when food availability was low, and when adult aggression score was low. High density nesting seems to have been imposed by the limited size of the island and prolonged population increase.     

Yolk androgens and begging behaviour in black-headed gull chicks: an experimental field study

Black-headed gulls, Larus ridibundus, produce clutches of three eggs, which contain high levels of maternal androgens in the yolk. These levels increase with laying order and the eggs hatch asynchronously. Experiments have supported the hypothesis that this within-clutch variation in maternal androgens mitigates the disadvantage of last-hatched chicks in sibling competition, by enhancing embryonic development and early posthatching growth. We hypothesized that these effects come about by the stimulating effects of maternal androgens on begging behaviour and competitive ability. In the field, we injected first-laid eggs of a clutch (which have a low androgen level) with either an androgen solution (T eggs) or vehicle (Oil eggs). We then created pairs of chicks hatched from Oil and T eggs, matched for egg mass and hatching date. Parent-chick interactions were recorded from observation hides. Chicks from T eggs hatched almost half a day sooner than those from Oil eggs. Furthermore, chicks from T eggs were more active during the first week after hatching, were more often the first to react to the approaching parent, begged more frequently, and obtained the larger share of food. We conclude that the enhancing effect of yolk androgens on growth in this species arises at least partly through androgen-mediated effects on the chicks' behaviour. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

Maternal androgens in black-headed gull (Larus ridibundus) eggs: consequences for chick development

We tested the hypothesis that mother birds counterbalance the negative effects of hatching asynchrony for later-hatched chicks by increasing the yolk androgen concentrations in consecutive eggs of their clutch. In doing so, they may adaptively tune each offspring's competitive ability and, thus, growth and survival. However, evidence in support of this hypothesis is contradictory. The yolk concentrations of maternal androgens in the eggs of black-headed gulls increase significantly with the laying order of the eggs in a clutch. We experimentally tested the functional consequences of this increase on chick development under natural conditions by injecting eggs with either an oil or androgen solution. We created experimental clutches in which androgen levels either stayed constant or increased with laying order while controlling for differences in egg quality by using only first-laid eggs. We then compared development, growth and survival between these broods. Androgen treatment enhanced embryonic development because androgen-treated eggs hatched half a day earlier than controls, while their size at hatching was similar to oil-treated controls. Androgen treatment did not increase chick survival, but it enhanced growth. Androgen-treated, third-hatched chicks had a higher body mass and longer legs than third-hatched chicks that hatched from oil-treated eggs. At the same time, growth of first chicks (which were all oil treated) was reduced by the presence of two androgen-treated siblings, suggesting that yolk androgens enhance the competitive ability of later-hatched chicks. Our results support the hypothesis that transfer of different amounts of androgens to the eggs of a clutch is a mechanism by which mothers maximize their reproductive output.     

Costs of large communal clutches for male and female Greater Rheas Rhea americana

The breeding system of the Greater Rhea Rhea americana is almost unique among birds as it combines harem polygyny and sequential polyandry, with communal egg-laying and uniparental male care. In this species, large communal clutches (more than 30 eggs) are rare and have a lower hatching success than smaller clutches. Here we analyse the proximate causes of hatching failures and the costs of large communal clutches (and therefore the costs of extensive polygyny) for males and females. We evaluated if length of the nesting period, egg viability, egg losses during incubation and male parental activity at the nest were affected by clutch size. We also evaluated if chicks hatched from large clutches have a lower survival during the first 2 months after hatching. Large clutches had longer nesting period and lower hatching success, mainly as a result of bacterial contamination of the eggs and increased hatching asynchrony. In addition, large clutches tended to lose more eggs as a result of accidental breakage or predation. Male activity at the nest and chick survival were not related to clutch size. Low hatching success, nest predation risk and energetic costs associated with large clutches penalize females that join large harems and males that accept additional eggs into the nest.     

5. BIRDS ON RIETFONTEIN FARM,LOOP SPRUIT VALLEY

Randall, R. M. &; Randall, B. M. 1981. Roseate Tern breeding biology and factors responsible for low chick production in Algoa Bay, South Africa. Ostrich 52:17-24.

Roseate Terns Sterna dougallii were studied in 1977 on St Croix Island, Algoa Bay, South Africa. They are winter breeders in Algoa Bay and remain away from the breeding islands until about three weeks before the first eggs are laid. Full breeding dress is usually attained by the time the chicks hatch, when red appears on the culmen. Reasons are given for regarding the red culmen as an intraspecific aggressive signal. Nest density was 0,2/m² with a mean nearest neighbour distance of 0,66 m ± 0,27 m. Mean size of first clutches was 1,32 eggs, of replacement clutches was 1,03 eggs. Eggs measured 42,1 mm (39,8-44,5 mm) x 30,1 mm (28,6-31,5 mm). In clutches of two eggs, first eggs had significantly larger volumes than second eggs. Incubation took about 25 days and one of the pair did most of the incubating. Rearing took less than 28 days and all the terns had left the island a week after the last chick first flew. Human disturbance, gull predation, intraspecific aggression, and rain were factors contributing to the low production of 33 flying young in 1977. An estimated production of 79 flying young was calculated as necessary to maintain the population of 74 breeding pairs.     

Rates and consequences of relaying in Cassin's auklets Ptychoramphus aleuticus and rhinoceros auklets Cerorhinca monocerata breeding in a seasonal environment

We removed first eggs from early‐laying females to measure rates and consequences of relaying in Cassin's auklets Ptychoramphus aleuticus and rhinoceros auklets Cerorhinca monocerata at Triangle Island, British Columbia, Canada. Based on egg size and composition, the investment that Cassin's auklets made in first eggs was very close to that predicted from adult body mass, whereas rhinoceros auklets invested more. In both species, a high percentage of females relaid (90% of Cassin's and 87% of rhinoceros auklets). Breeding success declined weakly with later laying among control Cassin's auklet pairs, but pairs that we induced to relay bred more successfully than naturally late pairs, and similar to values predicted from laying dates of their first eggs. Their chicks also fledged heavier and younger than late control chicks, and similar to values in early control chicks, but followed the population‐wide seasonal decline in wing length at fledging. Nestling diets were dominated by Neocalanus copepods until late in the season, a sign that feeding conditions remained favourable until late. In contrast, rhinoceros auklet pairs induced to relay followed the population‐wide seasonal decline in breeding success, which was driven by a decline in hatching success. Pacific sandlance Ammodytes hexapterus, thought to be a preferred prey species, virtually disappeared from nestling diets in mid‐to‐late season, yet there was no seasonal decline in fledging mass. However, chicks from replacement eggs followed the declines among control chicks in both age and wing length at fledging. Despite the female having produced a replacement egg, and despite delayed breeding, there appeared to be little immediate consequence associated with relaying for Cassin's auklets, except for a tendency for their chicks to fledge with short wings. Consequences were more marked in rhinoceros auklets (greatly reduced hatching success, and having their chicks fledge with short wings), and this may have been due to the large investment made in eggs, and/or to delayed breeding. Results of this study show that attributes of Cassin's and rhinoceros auklets that lay at different times in the season can be important in driving seasonal declines in breeding performance, as found in studies on other Alcidae. They also show how decisions taken during the egg stage can have variable yet potentially important implications for fitness, even in relatively long‐lived species that lay single‐egg clutches.