Pre-incubation feeding activities and energy budgets of Snow Geese: can food on the breeding grounds influence fecundity?

The potential contribution of early spring feeding conditions in the Arctic to clutch size variation was examined in a population of Lesser Snow Geese Anser caerulescens caerulescens. Behavioural observations were combined with energetic analyses of food material to derive an estimate of the energy budgets of pre-laying and laying females. Food intake of females between arrival on the breeding grounds and incubation was considerable; estimated energy gains in this period were in the same magnitude as the cost of one or several eggs. The pre-laying period spent on the breeding grounds can thus be energetically beneficial rather than costly. Accumulation of resources for reproduction in Snow Geese is a continual process including the breeding grounds, and nutrient limitation after arrival in the Arctic cannot sufficiently explain the environmental component of clutch size variation. The timing of migration and follicle development is such that clutch size decisions are sometimes made during the late stages of migration and some-times after arrival. In the latter case food conditions on the breeding grounds may greatly influence clutch size; in the former case they may still influence readjustments of clutch size after the initial decision. The universal negative correlation between clutch size and laying date in Snow Geese can be explained by negative fitness consequences of late hatching, which outweigh the benefits of delayed laying and further nutrient accumulation. Food shortage on the breeding grounds may sometimes be a secondary factor contributing to seasonal clutch size decline.     

Handicapped females receive more feedings during incubation from their mates: support for the female nutrition hypothesis

The female nutrition hypothesis posits that provisioning intensity of incubating females by their mates may depend on female needs and ensure proper incubation and a corresponding high hatching and breeding success of breeding pairs. Here, we have handicapped female pied flycatchers Ficedula hypoleuca at the beginning of incubation by clipping two primaries on each wing and filmed nests during incubation and later nestling provisioning to estimate male involvement in incubation feeding at the nest and in offspring care. Incubation feeding was more frequent at late nests. Correcting for this seasonal effect, incubation feeding was significantly affected by treatment and twice as high at experimental as at control nests. There was no effect of the experiment on female incubation attendance. The handicap did not result in any effect on hatching and breeding success, nestling growth and male or female provisioning and mass at the end of the nestling period. Males adjust their incubation feeding activity at the nest to female energetic requirements during incubation.     

Body mass patterns of Little Stints at different latitudes during incubation and chick-rearing

Due to the ‘double‐clutch’ mating system found in the arctic‐breeding Little Stint Calidris minuta, each parent cares for a clutch and brood alone. The resulting constraint on feeding time, combined with the cold climate and a small body size, may cause energetic bottlenecks. Based on the notion that mass stores in birds serve as an ‘insurance’ for transient periods of negative energy balance, but entail certain costs as well, body mass may vary in relation to climatic conditions and stage of the breeding cycle. We studied body mass in Little Stints in relation to breeding stage and geographical location, during 17 expeditions to 12 sites in the Eurasian Arctic, ranging from north Norway to north‐east Taimyr. Body mass was higher during incubation than during chick‐rearing. Structural size, as estimated by wing length, increased with latitude. This was probably caused by relatively more females (the larger sex) incubating further north, possibly after leaving a first clutch to be incubated by a male further south. Before and after correction for structural size, body mass was strongly related to latitude during both incubation and chick‐rearing. In analogy to a similar geographical pattern in overwintering shorebirds, we interpret the large energy stores of breeding Little Stints as an insurance against periods of cold weather which are a regular feature of arctic summers. Climate data showed that the risk of encountering cold spells lasting several days increases with latitude over the species’ breeding range, and is larger in June than in July. Maintaining these stores is therefore less necessary at southern sites and during the chick‐rearing period than in the incubation period. When guarding chicks, feeding time is less constrained than during incubation, temperatures tend to be higher than in the incubation period, reducing energy expenditure, and the availability of insect prey reaches a seasonal maximum. However, the alternative interpretation that the chick‐tending period is more energetically stressful than the incubation period, resulting in a negative energy balance for the parent, could not be rejected on the present evidence.     

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.     

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.     

Effects of individual life-history traits and weather on reproductive output of Black-headed Gulls Larus ridibundus breeding in the Wadden Sea, 1991–97

Capsule Annual breeding success was relatively constant and is shown to be related to clutch size and growth rate and to be positively affected by rain during egg-laying and advanced chick-rearing phase.

Aims To provide the first long-term data on breeding success of Black-headed Gulls in the Wadden Sea, to analyse its intrinsic and environmental co-variates, and to re-assess the significance of the severe winter 1995/96 on reproduction.

MethodsIn a relatively small colony at the Wadden Sea coast, clutches were selected randomly and enclosed to determine clutch size, egg biometrics, hatching and breeding success, and chick development in 1991 and from 1994 to 1997. Weather data (temperature, rain, wind) were related to life-history traits (clutch size, egg volume, chick development) and reproductive success.

Results Mean annual breeding success was 0.7 fledglings per pair. In 1996, breeding success tended to be lower and chick growth rate was significantly lower. Hatching success was lower in small clutches, chick mortality increased with decreasing chick growth rate. Rain during the egg-laying phase increased clutch size and decreased clutch predation. Rain during the early post-natal phase impaired chick growth. Rain during the phase of linear growth affected chick growth and fledging success positively and brood predation negatively.

Conclusions Breeding success of Black-headed Gulls breeding in the Wadden Sea is relatively constant between years, probably due to the use of terrestrial and marine feeding habitats. Rain may increase the availability of intertidal and terrestrial prey and thus may affect time budgets and food provisioning of parents positively. Lower breeding success in 1996 might have been caused by a relatively dry breeding season and possibly by the preceding severe winter.     

SHORT NOTES

Earlé, R. A. 1981. Factors governing avian breeding in Acacia savanna, Pietermaritzburg, Part 3: Breeding success, recruitment and clutch size. Ostrich 52:235-243.

The clutch size and breeding success of eight species of birds were monitored over a two year period in Acacia savanna. The mean clutch size fluctuated within the breeding season and four patterns of clutch size variation were noted. A smaller proportion of large clutches were laid in the 1979 season when less food was available. Breeding success was higher in the dry 1979 season but fewer breeding attempts were made and the overall recruitment was thus lower. At the peak of the breeding season, in mid-November, breeding success was at its lowest. Predation on nests was the greatest factor reducing breeding success although rain and strong winds affected some species.     

Reproductive ecology of the lacertid lizard Podarcis bocagei

This paper presents data on aspects of the reproductive ecology of a population of Podarcis bocagei in northwestern Spain, as monitored over a two-year period (1990–1991) Data were obtained principally on the basis of mark-recapture experiments, but also from laboratory hatching studies Mating took place between the end of March and July During the laying period, from May to July, 8 5% of reproductive females produced three clutches, 52 1% two clutches, and 39 4% one clutch In general, single clutches were produced by small females Only a small proportion of large females produced three clutches Mean clutch size was 4 8 eggs (range 4–7) in May, 4 3 (2–6) in June and 3 9 (2–4) in July There was sigmficant variation in the mean snout-to-vent length (SVL) of females laying in each month of the season Both clutch size and mean single-egg volume increased with mother's SVL There was a significant partial correlation between egg volume and clutch size when both mother's SVL and month of laying were held constant There was no significant between-year variation in clutch size, breeding females' SVL, egg weight or relative clutch mass A delay in the timing of reproductive events in one year (1991) is attributable to adverse weather conditions during early spring Hatching occurred between July and September Hatch success (as estimated in 1989, 1990 and 1991 from natural nests at the study site) was high, ranging from 83% in 1991 to 91% in 1989 The mean SVL of female hatchlings was greater than that of male hatchlings By contrast, adult females had lower mean SVL than adult males     

Breeding biology of the Little Egret Egretta garzetta on the southern coast of the Bay of Biscay

ABSTRACT

Capsule: Annual reproductive parameters of Little Egrets Egretta garzetta in an Atlantic coastal colony showed strong variation in a 20-year study, mainly due to extreme events.

Aims: To describe the breeding biology of Little Egrets in the Bay of Biscay and compare it with that of the Mediterranean basin. Also, to explore relationships between breeding parameters and colony size with some climatic indicators.

Methods: Phenology, number of nests, clutch size, number of hatchlings, brood size, and hatching and breeding success were recorded over 20 years.

Results: Median laying date of 214 nests was 1 May (range: 1 April–25 June) and 54% of the clutches were laid in the second half of April and the first half of May. Over the 20-year study period mean clutch size of 270 nests was 4.0, mean number of hatchlings was 3.1, and mean brood size was 2.3. Hatching success ranged from 46.1% to 100% and breeding success from zero to 100%. Number of nests was negatively associated with clutch and brood size. The highest clutch size and lowest brood size were recorded at the beginning of the season. Significant relationships were found between the number of hatchlings and the rainfall during the pre-breeding season, and between brood size and the summer rainfall.

Conclusions: Reproductive parameters showed significant variation over the study period, which highlights the importance of using long-term data sets. Breeding occurred one month later than in natural colonies of the Mediterranean basin. Negative relationships between the number of nests and clutch and brood size suggest some degree of density-dependent effects. Ranges of clutch size, number of hatchlings, and brood size were within those reported in Mediterranean populations. The effect of rainfall on reproductive parameters was weak. Extreme weather and predation events caused low rates of hatching and breeding success that affected the growth of the colony.     

Variation in breeding parameters of Eleonora’s falcon (Falco eleonorae) and factors affecting its reproductive performance

We gathered data for a four-year period (2004?C2007) on the nesting ecology and reproductive performance of Eleonora??s falcon in the Aegean Sea. We investigated in an indirect way the relation between clutch size and pre-laying food availability, the significance of site and pair quality on productivity, and the effects of habitat and intraspecific competition on breeding success. Overall, the species selected nest sites sheltered from sun exposure but not from the prevailing wind. Hatching, fledging, and breeding success rates were estimated at 64, 72%, and 60%, respectively. Fledglings per breeding pair ranged from 1.19 to 1.75, and fledglings per successful pair from 1.84 to 2.0, between the years. Productivity depended on parental care rather than nest-site quality. Breeding parameters varied significantly between the years, exhibiting a strong spatial yet local effect. Low success rates were recorded in specific colonies, which were attributed to adverse weather conditions and habitat degradation. Insect food availability prior to egg-laying, estimated via plant biomass, was positively correlated to clutch size. Meanwhile, low wind strengths in August, large distances from the mainland, and population size in the vicinity of the colonies had negative effects on breeding success. Considering data at the Mediterranean scale, a longitudinal trend is observed across the breeding range of this species, with breeding parameters slightly decreasing from west to east.     

棕背黑头鸫繁殖习性初步观察

2008年和2009年的4～8月,在四川省雅江县帕姆岭对棕背黑头鸫Turdus kessleri的繁殖生态进行了初步观察.该鸟繁殖期在4月下旬至7月上旬,营树上巢,营巢树种为高山栎Quercus aquifolioides和鳞皮冷杉Abies squamata.窝卵数为2~3枚(n=7),平均卵重(7.96±0.03)g(n=8),卵长径(32.7±0.17)mm,短径(21.9±0.13)mm(n=13),雌雄共同孵卵,以雌性为主,孵化期为15~17 d(n=2),孵化率为83.3%(n=18).雌雄共同育雏,以雄性为主,雏鸟出飞后主要在巢周围的林下或灌从活动,这时亲鸟仍会对幼鸟喂食.在同一繁殖季对巢有重复利用的现象.     

Experimentally induced clutch size enlargements affect reproductive success in the Pied Flycatcher

We performed a food provisioning experiment in a population of Pied Flycatchers Ficedula hypoleuca breeding at high altitude in central Spain to test if food availability before and during laying determines clutch size. Food was provided to one of two pairs with the same date of initiation of nest-building (15 dyads of subsequently reproducing pairs were thus created). Food provisioning began on the day of initiation of nest-building and ended on the day after the last egg was laid. Although laying date was unaffected by the experiment, clutch size in the experimental treatment was significantly larger. This result could indicate that food availability at laying (1) proximately constrained clutch size or (2) that females evaluated future conditions for incubating eggs and feeding nestlings based on food availability at laying. Reproductive success (proportion of eggs that resulted in fledged young) was significantly reduced in the experimental treatment. This effect suggest that supplemented females were tricked by the experiment into laying more eggs than the number of eggs they were able to incubate with success and the number of nestlings they were able to feed, a source of error in clutch size adjustment which could be common in non-experimental situations.     

Nestling growth and mortality of Pied Flycatchers Ficedula hypoleuca in relation to weather and breeding effort

The growth pattern and mortality of young Pied Flycatchers Ficedula hypoleuca were studied to focus on the mechanisms and constraints behind the widely studied optimization of clutch size. The clutch sizes were modified, and the growth and survival of chicks from different clutch sizes were monitored along with the prevailing weather during the nestling period to detect the effect of weather on reproductive success. The weather conditions during the feeding period of the nestlings varied within a season as well as between breeding seasons. The prevailing weather markedly affected both the growth rate and the survival of chicks, yet, the effects of weather on growth were not greater in enlarged clutches. The impact of adverse weather was more pronounced in the later phases of nesting, when the food demand of a brood was highest. Brood reduction and total nest losses were more likely during extensive rainfall during the nestling phase and also in the enlarged clutches. Thus, weather is a very important determinant of reproductive success in this species. Weather conditions during the breeding season are unpredictable, however, and therefore brood reduction through sibling competition is a mechanism whereby brood size can be adjusted to the level the parents can rear under the prevailing conditions.     

THE INFLUENCE OF THE ENVIRONMENT ON BREEDING SUCCESS OF A SUBURBAN POPULATION OF CRESTED BARBETS TRACHYPHONUS VAILLANTII

Van Zyl, A.J. 1994. The influence of the environment on the breeding success of a suburban population of Crested Barbets Trachyphonus vaillantii. Ostrich 65: 291–296.

I studied the breeding biology of the Crested Barbet Trachyphonus vaillantii in Colbyn, a suburb east of Pretoria, South Africa, for nine breeding seasons from 1981 to 1989 to examine patterns in annual breeding success, breeding attempt success in multiple broods, and rainfall. The modal incubation period was 14 days and the nestling period ranged from 28 to 31 days. Average clutch size for all the years was 3,3 eggs/clutch and there was no significant difference in clutch size or number of young fledged/nest between years. On average, Crested Barbet pairs made 2,4 breeding attempts/season. There was no difference in clutch size or breeding success between the breeding attempts. Crested Barbets nesting in natural nests laid on average larger clutches than those in artificial nestboxes, but had non-signficantly lower breeding success. Failure to raise Crested Barbet chicks was attributed to parasitism by Lesser Honeyguides Indicator minor, bee swarms occupying nestboxes, and flooding of natural nests. Breeding performance was not correlated with rainfall or adult body size. The suburban environment may be less variable than a natural environment, resulting in a stable breeding Crested Barbet population.     

Differential maternal investment counteracts for late breeding in magpies Pica pica: an experimental study

Reproductive success in many avian populations declines throughout the breeding season. Two hypotheses have gained attention to explain such a decline: the "timing" hypothesis proposes that deteriorating food availability causes the decline in reproductive success (causal effect of breeding time), whereas the "quality" hypothesis proposes that individuals of lower phenotypic quality reproduce at the end of the breeding season, causing the correlation between breeding time and breeding success. We tested both of these hypotheses in a monogamous single breeder, the magpie Pica pica , by experimentally inducing some pairs to lay a replacement clutch, after removal of the first clutch. The first clutch was left in the nest of another magpie pair (matched by laying date and clutch size), and incubated and raised by these foster parents. In this way we obtained two clutches from the same magpie pair with full siblings raised in conditions of the first and second reproductive attempts. High quality pairs (with laying dates in the first half of the breeding season) reached similar breeding success in replacement clutches as compared to first clutches of the same female. In addition, experimental pairs reared significantly more offspring of similar quality in their replacement clutches as compared to late-season first clutches, thereby suggesting that late season first clutches were produced by pairs of lower phenotypic quality. Results indicate that high quality pairs trade-off clutch size for larger eggs in replacement clutches, which could help magpie pairs to partly compensate for poorer environmental conditions associated with a delayed breeding attempt.     

Reversed sexual size dimorphism in raptors: evaluation of the hypotheses in kestrels breeding in a temporally changing environment

Reversed sexual size dimorphism (RSD, females larger than males) is commonly found in birds of prey. We used kestrels (Falco tinnunculus), breeding in western Finland in a temporally varying environment of 3-year vole cycles, to assess current hypotheses for the evolution and maintenance of RSD. Our 12-year data showed only weak correlations between parental size and breeding parameters (laying date, clutch size and the number of fledglings produced). The degree of RSD per se was unrelated to breeding success, contrary to the prediction of the female dominance hypothesis. Females with small males produced larger clutches in low-vole years, independently of laying date, which supports the small male (or its equivalent inter-sexual selection) hypothesis. Small females tended to have more fledglings, particularly in low-vole years, which is inconsistent with the hypotheses for an advantage of large female size (the starvation, intra-sexual selection, reproductive effort, and supplementary feeding hypotheses). As for males, smaller females may be more efficient hunters, the importance of which should be most pronounced under harsh breeding conditions. Our results suggest that the directional selection on a particular size in kestrels may be under contrasting selection pressures by the environment, and, at least in breeding females, the advantages of large size can actually be counterbalanced during harsh environmental conditions. Received: 7 May 1999 / Accepted: 20 January 2000     

The breeding biology of the Namaqua Sandgrouse,Pterocles namaqua

The breeding biology of the Namaqua Sandgrouse, Pterocles namaqua, was studied and its nesting success determined through the observation of 278 nests over four consecutive breeding seasons at Droëgrond, Northern Cape Province, South Africa. The normal clutch of three eggs is laid over five days (±48-hour laying interval). The incomplete clutch is left unattended overnight, but is attended during the heat of the day by the female on days when an egg is laid and by the male on alternate days. After clutch completion, the pair share incubation, with the female relieving the male 151 min (±21 S.D.) after sunrise and the male relieving the female 105 min (±21 S.D.) before sunset. The incubation period is 21 days from clutch completion, and the three chicks normally hatch within 18 hours of one another. Nesting success ranged from 5.7% to 13.5% between seasons and averaged 8.2%. Predation, primarily by small mammals, was responsible for 96% of nest losses. Estimates of annual recruitment at Droëgrond ranged from minima of 3–10% to maxima of 6–20%, and are believed to be representative of a core area of the distribution of the Namaqua Sandgrouse in South Africa. These low estimates suggest that annual juvenile recruitment may be too low to maintain Namaqua Sandgrouse populations locally. Possible reasons for the sustained low level of breeding success are discussed.     

吉林白城地区草原栗斑腹(巫鸟)窝卵数、营巢成功率和繁殖成功率的研究

对分布于吉林白城地区草原生境中栗斑腹巫鸟的窝卵数、营巢成功率和繁殖成功率的初步研究结果表明 ,繁殖期栗斑腹巫鸟种群的平均窝卵数为 5 .0 9± 0 .5 8枚 /巢 ;窝卵数与产卵期、出巢数与产卵期、窝卵数与卵大小之间呈负相关 ,产卵期与孵化率之间存在极显著的负相关关系 ,巢外径与窝卵数之间存在显著的正相关关系 ,巢的其余指标均与窝卵数呈正相关 ;平均孵化期为 12± 0 .4 9d ,孵化率为 36 .3% ,繁殖成功率为 11.11% ;7日龄以上的雏鸟群体大小为 2 .5 6± 1.5 3只 ,栗斑腹巫鸟的雏鸟存活率为 2 7.6 9% .     

Photoperiodic control of reproduction and molt in the kestrel, Falco tinnunculus

An adaptive decline in average clutch size with progressive date of laying is characteristic of most bird species with a single clutch of variable size per year. The effect of photoperiod on timing of laying, clutch size, and subsequent molt was investigated in kestrel pairs breeding and raising their young in captivity. In natural daylight (nLD), clutch size, under ad libitum feeding, showed the same decline with date as in nature. Birds breeding later also started molt later and molted faster (more feathers simultaneously), so that all birds completed molt more or less at the same time. Constant long days (LD 17.5:6.5 and LD 13:11) from December 1 onward advanced both reproduction and molt. The LD 17.5:6.5 group developed the reproductive system faster, had a shorter courtship period, and laid eggs earlier than the LD 13:11 group. In both photoperiods there was a decrease in clutch size with progressive laying date, similar to that in nLD. Molt started in both groups at about the end of the laying period and slowed down in the longer photoperiod, especially in males. Plasma luteinizing hormone (LH) changes in the two photoperiods were different for males and females. Males showed the expected slower LH response in the shorter photoperiod, but the initial LH response by females was the same in both photoperiods. Data on LH, reproductive behavior, and body mass suggest that females have a wider annual reproductive window than males. Data on time of laying and number of eggs suggest that clutch size in the kestrel is determined by laying date itself, following an endogenous rhythm that is phase-locked to the reproductive cycle.