4. UNUSUAL EXPERIENCES WITH BIRDS

Earlé, R. A. 1989. Breeding biology of the Redbreasted Swallow Hirundo semirufa. Ostrich 60: 13–21.

The two races of the Redbreasted Swallow Hirundo semirufa seem to have separate breeding seasons with the northern race H. s. gordoni breeding April-July, while most records for the nominate race fall in October-February. All nests studied were in concrete culverts less than 1 m high. Eggs laid in second clutches by individual females weighed significantly less than eggs laid in first clutches. Eggs hatched on average 16,2 days after incubation started or 18–21 days after the eggs were laid. Only females incubated. Chicks fledged 23–25 days after hatching and reached a maximum body mass of about 31,5 g on day 18 before a steady decline in mass until fledging. Most nesting failures resulted from infertile eggs or starvation of young in the nest (16,2% of all young starved). Overall breeding success was 60,6%. In all, 81,8% of first clutches produced fledglings but only 44,4% of second clutches. Over a three year period 4,9 young were produced per pair breeding in the area (1,6 young/pair/breeding season).     

Breeding biology of the Barn Owl Tyto alba in central Mali

Data were obtained on 178 clutches of African Barn Owls in central Mali from four breeding seasons during 1979–1983. Significantly more clutches were laid in 1979–1980 and significantly fewer in 1980– 1981 than the average for the 4 years and there were significantly more clutches laid in the middle period of the annual breeding season. The egg volume was significantly smaller at the beginning of the breeding season and significantly larger in the middle than the overall mean with eggs of second clutches being larger than those of first clutches. The clutch size was 605 eggs of which 479 hatched. The number of young fledged per successful nest was 319 and was 1 83 for all nesting attempts. The month was the only variable shown to affect significantly the clutch size, eggs hatched and fledging rate, the highest success rates being associated with the middle of the breeding period. The average interval between the hatching of eggs was 2–31 days. Survival rates (47'1%) to fledging were significantly affected by year (1981–1982 being the least) and month (mid-season birds the best). The order of hatching significantly affected age at death or disappearance, the first-hatched birds surviving the longest. The year significantly affected age at fledging, the young from the year in which most clutches were laid leaving the nest at the youngest age and those associated with the year having the least number of clutches remaining in the nest the longest. The month of hatching also affected fledging age, birds at the extremes of the breeding season fledging at older ages. The discussion compares these data with those from elsewhere.     

THE BIRDS OF LANGEBAAN LAGOON

Data are presented on breeding success of Red Bishops (Euplectes orix) collected over four breeding seasons at a colony in the Addo Elephant National Park, Eastern Cape, South Africa. Overall hatching and fledging success were 53.8% and 26.0% of all eggs laid, respectively, and the overall mean number of fledglings per breeding attempt was 0.77. Hatching and fledging success varied significantly among seasons, with both clutch and brood losses due to predation being the main reason for the observed differences. Hatching success also differed significantly among clutch sizes, being highest for four-egg clutches (63.2%), intermediate for three-egg clutches (55.5%) and lowest for two-egg clutches and five-egg clutches (33.2% and 34.3%, respectively). However, fledging success was not significantly different among clutch sizes. The mean number of fledglings per breeding attempt was 0.44 for two-egg clutches, 0.80 for three-egg clutches, 1.10 for four-egg clutches, and 0.57 for five-egg clutches. The height of accepted nests (i.e.nests in which at least one egg was laid) was significantly lower than the height of nests not accepted. In addition, accepted nests in which eggs hatched and young fledged were significantly lower than accepted nests in which no eggs hatched and no young fledged. These overall effects of nest height on nest acceptance and hatching and fledging success were, however, due only to nests built above water, since no such effects were found when nests built above ground (i.e.on dry land) were analysed separately. I detected no effect of nest coverage on the probability of a nest being accepted, nor was there any effect of nest coverage on hatching or fledging success. Nests above water were significantly more likely to be accepted than nests above ground; however, hatching and fledging success of nests that were accepted did not differ significantly between nests built above water and those built above ground.     

A long-term large-scale study of the breeding biology of the Spanish imperial eagle (Aquila adalberti)

We present data from a 17-year study of the population biology of a growing population of Spanish imperial eagles Aquila adalberti across most of its breeding range. The objective of this study was to analyse the effects of age, supplemental feeding and rabbit haemorrhagic disease (RHD) on several breeding parameters of this population of eagles. Average clutch size was 2.2 eggs per clutch, and the average incubation time was 41.7 days per clutch. Fledging occurred an average of 76.8 days after hatching, the length of the fledgling period was not correlated to clutch size. The annual average percentage of pairs laying eggs was 88%. A significant reduction in the percentage of pairs laying eggs in the period 1992–1994 (from 91 to 81%) coincided with most of the eagles’ territories being affected by the rabbit epizootic disease, RHD, which reduced their food supply significantly. Average productivity was 1.23 chicks per monitored territory, average breeding success was 1.40 chicks in a clutch per territory and the average fledging rate was 1.69 chicks per territory with hatching success. The main known causes of breeding failure during incubation were nest collapse and human disturbance. During chick-rearing, total or partial chick losses were mainly caused by siblicide, disease, malnutrition or nest collapse. In 26.2% of the 1372 monitored breeding attempts, at least one of the breeding birds was a subadult (the male in 56.1% of the cases, the female in 15.5% and both sexes in 28.4% of cases). In cases of mixed-aged pairs (n = 205), 70.7% were the result of a substitution, and 29.3% were the result of the forming of a new pair. Egg laying took place significantly earlier and breeding success was higher in territories occupied by adults than in those occupied by subadults. Breeding parameters were higher in high-quality (rabbit-rich) territories than in low-quality (rabbit-poor) territories, but only for those territories occupied by adults. The values obtained in the territories occupied by adults were only significantly higher than in those of the subadults in high-quality territories. Age and territory quality thus simultaneously affected reproductive output.     

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.     

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.     

Reproductive success of the Kittiwake Rissa tridactyla: the roles of clutch size, chick growth rates and parental quality

Kittiwake growth rates and breeding success are examined in relation to survival between fledging and breeding and to adult survival rates. High chick growth rates lead to increased survival after fledging. Broods of three (the maximum brood size) did not suffer lower fledging success than broods of two and clutches of three fledged appreciably more chicks per pair than did clutches of two or one. On average, the a- and b -chicks in broods of three grew at a faster rate and had a higher survival before breeding than those from smaller broods. Chicks from broods of two with experienced female parents grew at a faster rate than those of inexperienced female parents. Female parents which laid three egg clutches had a higher survival rate than those which laid clutches of two or one. We contend that three egg clutches were laid by higher quality individuals. We believe that clutch size indicates the condition of the Kittiwakes forming the pair. This condition probably has a genetical component, but is modified by environmental factors.     

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.     

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.     

Reproductive biology of the endangered Ouvea Parakeet Eunymphicus cornutus uvaeensis

The reproductive biology of the endangered Ouvea Parakeet Eunymphicus cornutus uvaeensis , an endemic subspecies of Ouvea island (Territory of New Caledonia, Southwest Pacific) was studied from June 1994 to February 1996. Breeding was recorded from early August until late January. All nests were sited in cavities of native forest trees, 90% of them in Syzygium sp. and Mimusops sp. Mean clutch size was 2.9 eggs (range 2–3), and double clutches were recorded. Incubation lasted 21 days and the nestling period averaging 43 days. An average of 1.65 chicks fledged per nest but only 0.75 per breeding pair were still alive 30 days after fledging. The main causes of chick loss were starvation of the third sibling during the first week due to hatching asynchrony, raptor (presumably Brown Goshawk) predation of fledglings and human harvest for the pet trade. Growth curves and multiple regressions of weight, culmen-width and -length, tarsus- and wing-length, showed that wing-length was a good predictor of age, and that there were significant differences between the sexes for weight and culmen-width. The pattern of the breeding season, brood reduction, nest-site characteristics and presumed size of breeding territories suggest that both food and availability of suitable nest-sites may be factors limiting breeding productivity. Proposals for conservation of this endangered bird are presented.     

Proceedings of the New Zealand Society for Parasitology Inc.

Abstract

A study of the nesting habits and breeding biology of blue penguin Eudyptula minor was undertaken over the 1995–96 and 1996–97 breeding seasons on Matiu‐Somes Island, Wellington, New Zealand. Male and female blue penguins tended to be faithful to both mates and nest sites, although there was insufficient evidence to detect any association between a bird's breeding success in 1995 and a subsequent change of mate or nest in 1996. Over the 1995 and 1996 seasons the recorded hatching success (0.51 ±0.11 and 0.63 ± 0.10 respectively), fledging success (0.81 ±0.12 and 0.85 ±0.10 respectively) and reproductive success (0.41 + 0.11 and 0.54 ± 0.11 respectively) were similar each season. There was no significant difference between the proportion of eggs laid, or eggs hatched and chicks fledged, between the two seasons. The mean number of chicks raised over the two seasons was 0.94 ± 0.05 per nest. Replacement clutches were laid by 11 per cent of failed breeders in each season, but only in 1996 were they successful in fledging chicks.

No significant difference was found between the breeding success of the Matiu‐Somes Island blue penguin colony recorded during this study and a previous study undertaken on the island 40 years ago.     

A cross-fostering experiment between the endangered takahe (

New Zealand's avifauna is characterised by a variety of endemic, often flightless, birds most of which are critically endangered. One of these, the takahe, is a large flightless rail which has been reduced to one population of 115 birds in its natural alpine habitat plus 52 others introduced on four small offshore islands. By contrast the takahe's closest extant relative, the pukeko, has been highly successful since its invasion of New Zealand within the past 800 years. This paper summarises results of a pilot study in which takahe eggs were cross-fostered to pukeko nests on Mana Island in order to increase the number of juveniles produced by each pair of takahe. Over two seasons, 67% (8/12) of the cross-fostered eggs hatched successfully with 25% (2/8) of the resulting young surviving to one year of age. These results were not significantly different from 42% (5/12) and 40% (2/5) hatching and fledging success of takahe-reared eggs from the same clutches. Low fledging success of cross-fostered chicks may reflect poor quality of takahe eggs per chicks rather than poor parental care by the pukeko foster parents, as hatching success of all parent-reared takahe eggs on Mana Island was only 22% (5/23) over the course of this research.     

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.     

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.     

Reproductive tactics of the ringed plover Charadrius hiaticula

Reproductive tactics of ringed plovers Charadrius hiaticula were studied at three localities in SW Sweden during five seasons. The usual clutch size is four, but removal experiments showed that females can produce five eggs in succession, with similar intervals between all eggs. High predation made mean breeding success per clutch low, 6.3% of eggs resulting in fledged young. Replacement clutches were common, and many pairs laid again after rearing their first brood to fledging. Egg laying spanned three months, much longer than for other waders in this region. Between years, reproductive success varied unpredictably with time of the season, but averaged over several years, the expected success was low and similar for the different parts of the breeding season. Chicks from late clutches had similar survival and recruitment as others. Because of the long breeding season and high rate of nest failure a female may produce up to five clutches of four eggs per season, containing in total about 3.7 times her own mass. Yearly local survival of adult females and males was estimated to 84.6 and 88.6%, respectively. Ability to produce many clutches with similar expected success throughout the season favours a long reproductive period, sometimes leading to double-brooding. Possible life-history trade-offs are discussed.     

Chick loss in the Falkland Skua Catharacta skua antarctica

Data on reproductive success of 110 Falkland Skua Catharacta skua antarctica pairs were gathered during the austral summers of 1988–1989 and 1990–1991 on New Island, Falkland Islands. Adults laid two eggs 2–3 days apart and began incubation with the first egg. For the years combined, 1.39 chicks per nest hatched and 0.84 chicks per nest fledged (fledging was defined as surviving to 16 days of age). Brood reduction was common; 43% of the two-chick broods were reduced to one, and mortality was concentrated on the younger chick. Although asynchronous hatching and differential death are consistent with Lack's brood reduction hypothesis, application of O'Connor's quantitative criterion revealed that sibling competition may not be responsible for the observed chick mortality. Furthermore, because no aggressive interactions between chicks were observed or detected indirectly, siblicide may be absent in this population. Instead, predation modified by a variety of factors may have led to the greater mortality of the second-hatched chick.     

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.     

ASPECTS OF McCORMICK SKUA BREEDING BIOLOGY

The breeding behaviour of the McCormick Skua was studied at Cape Royds, Antarctica, for three summers. These observations followed the work of Young (1963a, b). Records of banded birds suggest that at the age of five to six years birds return to breed in the area where they were reared. Breeding pairs retain the same territory and mate over consecutive summers. The male will retain a territory and remate if the female does not return, while there is some evidence to suggest that if the male is absent the female will leave the territory and remate elsewhere. Unfavourable weather frequently forced incubating birds to desert their eggs and as a result some pairs laid three clutches (at the most two clutches of two eggs and a clutch of one). The death of sibling chicks from fighting was examined by comparing the early growth of 11 successful pairs of chicks with that of 12 pairs in which one of the siblings died as a result of fighting. From a comparison of weights at hatching and the interval between the hatching of members of chick pairs, it appears that the difference in weight between twins and the gain in weight by one chick in the first few days is critical for the survival of the twins. The breeding success, calculated from the total eggs laid and the total number of chicks fledging, was 40%, 42% and 17% for the three respective summers. Storms (periods of wind with snow) were the main factor influencing breeding success.     

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.     

Experimentally Constrained Virulence is Costly for Common Cuckoo Chicks

Chicks of some avian brood parasites show high virulence by eliminating all host progeny in the nest whereas others develop in the presence of host nestmates. Common cuckoo ( Cuculus canorus ) chicks are typically highly virulent parasites as they attempt to evict all host eggs and chicks soon after hatching. However, several features of nest design, including steep walls and/or cavity nests, may effectively prevent cuckoo hatchlings from evicting nestmates. A previous observational study showed low success of cuckoo chicks in evicting progeny of a cavity nester host, the redstart ( Phoenicurus phoenicurus ) but cuckoo chicks showed low survival both when reared alone or in mixed broods with host nestmates. Whether poor cuckoo performance was caused by eviction costs and/or by the effect of presence of host chicks per se remains unclear. We experimentally cancelled any potential eviction costs by removing host eggs immediately after the cuckoo hatched and creating mixed broods 5 days later when the eviction instinct of the cuckoo already ceased. Cuckoos that were forced to compete with host nestlings experienced lower provisioning rates, poorer growth, and lower fledging success than control lone cuckoos. Cuckoos in mixed broods that survived until fledging fledged later, and at lower masses, than those in the sole cuckoo group. Thus, the cuckoo gens specializing on redstarts is similar to other cuckoo gentes, whose chicks are more successful in evicting host nestmates, and it does not benefit from the presence of host brood. Cohabitation with host nestlings then should be viewed as a maladaptive by-product of host cavity nest design.