The annual cycle of wing-moult and breeding in the Wattled Starling Creatophora cinerea

Moult, breeding and seasonal occurrence of the Wattled Starling Creatophora cinerea throughout its range in Africa are reviewed based on data from museum specimens and the published literature. Neither moult nor breeding follows a rigid seasonal pattern, although there are some regional differences, and overlap between moult and breeding is unlikely. The regular occurrence of interrupted wing-moult may be associated with nomadic movements rather than opportunistic breeding.     

The timing of birds' breeding seasons: a review of experiments that manipulated timing of breeding

Reproductive success usually declines in the course of the season, which may be a direct effect of breeding time, an effect of quality (individuals with high phenotypic or environmental quality breeding early), or a combination of the two. Being able to distinguish between these possibilities is crucial when trying to understand individual variation in annual routines, for instance when to breed, moult and migrate. We review experiments with free-living birds performed to distinguish between the 'timing' and 'quality' hypothesis. 'Clean' manipulation of breeding time seems impossible, and we therefore discuss strong and weak points of different manipulation techniques. We find that the qualitative results were independent of manipulation technique (inducing replacement clutches versus cross-fostering early and late clutches). Given that the two techniques differ strongly in demands made on the birds, this suggests that potential experimental biases are limited. Overall, the evidence indicated that date and quality are both important, depending on fitness component and species, although evidence for the date hypothesis was found more frequently. We expected both effects to be prevalent, since only if date per se is important, does an incentive exist for high-quality birds to breed early. We discuss mechanisms mediating the seasonal decline in reproductive success, and distinguish between effects of absolute date and relative date, for instance timing relative to seasonal environmental fluctuations or conspecifics. The latter is important at least in some cases, suggesting that the optimal breeding time may be frequency dependent, but this has been little studied. A recurring pattern among cross-fostering studies was that delay experiments provided evidence for the quality hypothesis, while advance experiments provided evidence for the date hypothesis. This indicates that late pairs are constrained from producing a clutch earlier in the season, presumably by the fitness costs this would entail. This provides us with a paradox: evidence for the date hypothesis leads us to conclude that quality is important for the ability to breed early.     

The timing of breeding and offspring size in Great Tits Parus major

The relationship between the timing of breeding, offspring weight and offspring recruitment was investigated in two populations of Great Tits Parus major. In two of six seasons a significant negative correlation was found between laying date and fledgling weight, in three seasons the opposite was true and in one season no significant correlation existed between these variables. Offspring recruitment was quantified in five seasons, and late-nesting birds were found to produce significantly fewer recruiting offspring in two of these, the same two seasons when late fledglings had significantly lower weights. No significant correlation existed between the number of recruits and laying date in the three seasons when late fledglings were as heavy as or heavier than early fledglings. The potential detriment to reproductive success of lateness thus was offset when late-nesting parents managed to produce heavy young. Between-year variations in the seasonal pattern of reproductive success has previously been suggested to contribute to the maintenance of variability in the timing of breeding in Great Tits. In this paper we suggest that producing heavy offspring late in the season might be a proximate factor influencing the seasonal patterns of reproductive success. Producing heavy offspring late in the season is probably not a "strategy" but rather an effect of chance differences between years in the seasonal availability of food or the seasonality of other factors important for the nesting birds.     

The timing of breeding and moult of the Lesser Striped Swallow Hirundo abyssinica

The Lesser Striped Swallow seems to have two different breeding populations. The birds south of 10°S breed largely during the spring and summer (July to April) and moult from about April to August. Birds further north breed throughout the year, but mainly during the first seven months of the year. Moult in the birds north of 10°S is from July to February when few birds are breeding. There seem to be two clearly defined moulting populations, with the southern breeding population moulting largely south of 10°S and the east African breeding population moulting largely north of the equator. In both populations moult and breeding seem to be separated in time, at least at the individual level.     

Eggs, egg formation and the timing of breeding

The eggs of birds contain all the nutrients necessary for the developing embryo. The female has to obtain these nutrients, and while in some species these may be gathered and stored over a period of time, in many species they seem to be obtained on a daily basis. Obtaining the calcium necessary for the eggshell may pose special problems for some species, which may have to give up valuable feeding time in order to search for calcium.
Egg size varies considerably, even within species, and the reasons for this are not clear. In the Great Tit Parus major , large eggs produce nestlings which have a higher chance of hatching, surviving to fledging and surviving after fledging. However, large eggs require the female to acquire more nutrients to form them, and large chicks may sometimes be at a disadvantage. The amount of energy required to form a larger egg often seems small unless the metabolic costs of egg formation are taken into account.     

Mating system and timing of breeding in Holarctic waders

In passerine birds polygamous species lay eggs later than monogamous species. Yom-Tov has hypothesized that this is because polygamous males do not provision their mates with food, thereby delaying egg-laying. An indirect prediction of this hypothesis is that there should be no difference in laving dates between monogamous and polygamous birds in which mate provisioning does not occur. This prediction was tested by examining egg-laying dates in sympatric wader species that have contrasting mating systems but in which food provisioning of mates does not occur. Polygamous waders laid eggs later than monogamous waders, however, both in a comparison involving only calidridine sandpipers and in a comparison involving sandpipers and plovers. Accounting for phylogeny did not affect the direction of the results, which therefore cast doubt on the validity of the 'mate provisioning' hypothesis and indicated that features common to both passerines and waders were more likely to explain the differences in egg-laying dates between mating systems. Mating system and parental care system were strongly related, with all polygamous species being uniparental and monogamous species being biparental. It is suggested that seasonally early food supplies are of relatively low abundance, constraining species to biparental care and monogamy. By contrast, seasonally late food supplies are more abundant, making uniparental care more successful, thereby creating greater opportunities for mate desertion and polygamy.     

The timing of breeding and moult of the Lesser Striped Swallow Hirundo abyssinica

The Lesser Striped Swallow seems to have two different breeding populations. The birds south of 10°s breed largely during the spring and summer (July to April) and moult from about April to August. Birds further north breed throughout the year, but mainly during the first seven months of the year. Moult in the birds north of 10°s is from July to February when few birds are breeding. There seem to be two clearly defined moulting populations, with the southern breeding population moulting largely south of 10°s and the east African breeding population moulting largely north of the equator. In both populationsmoult and breeding seem to be separated in time, at least at the individual level.     

Eggs, egg formation and the timing of breeding

The eggs of birds contain all the nutrients necessary for the developing embryo. The female has to obtain these nutrients, and while in some species these may be gathered and stored over a period of time, in many species they seem to be obtained on a daily basis. Obtaining the calcium necessary for the eggshell may pose special problems for some species, which may have to give up valuable feeding time in order to search for calcium.
Egg size varies considerably, even within species, and the reasons for this are not clear. In the Great Tit Pants major, large eggs produce nestlings which have a higher chance of hatching, surviving to fledging and surviving after fledging. However, large eggs require the female to acquire more nutrients to form them, and large chicks may sometimes be at a disadvantage. The amount of energy required to form a larger egg often seems small unless the metabolic costs of egg formation are taken into account.     

The influence of breeding phenology on the genetic structure of four pond‐breeding salamanders

Understanding metapopulation dynamics requires knowledge about local population dynamics and movement in both space and time. Most genetic metapopulation studies use one or two study species across the same landscape to infer population dynamics; however, using multiple co‐occurring species allows for testing of hypotheses related to different life history strategies. We used genetic data to study dispersal, as measured by gene flow, in three ambystomatid salamanders (Ambystoma annulatum , A. maculatum , and A. opacum ) and the Central Newt (Notophthalmus viridescens louisianensis ) on the same landscape in Missouri, USA . While all four salamander species are forest dependent organisms that require fishless ponds to reproduce, they differ in breeding phenology and spatial distribution on the landscape. We use these differences in life history and distribution to address the following questions: (1) Are there species‐level differences in the observed patterns of genetic diversity and genetic structure? and (2) Is dispersal influenced by landscape resistance? We detected two genetic clusters in A. annulatum and A. opacum on our landscape; both species breed in the fall and larvae overwinter in ponds. In contrast, no structure was evident in A. maculatum and N. v. louisianensis , species that breed during the spring. Tests for isolation by distance were significant for the three ambystomatids but not for N. v. louisianensis . Landscape resistance also contributed to genetic differentiation for all four species. Our results suggest species‐level differences in dispersal ability and breeding phenology are driving observed patterns of genetic differentiation. From an evolutionary standpoint, the observed differences in dispersal distances and genetic structure between fall breeding and spring breeding species may be a result of the trade‐off between larval period length and size at metamorphosis which in turn may influence the long‐term viability of the metapopulation. Thus, it is important to consider life history differences among closely related and ecologically similar species when making management decisions.     

Subject: Eggs, clutches and the timing of breeding

Research Notes on Avian Biology 1994: Selected Contributions from the 21st International Ornithological CongressGeneral Biology: Clutch Size and Time

Subject: Eggs, clutches and the timing of breeding     

Delayed timing of breeding as a cost of reproduction

Timing of breeding is a trait with considerable individual variation, often closely linked to fitness because of seasonal declines in reproduction. The drivers of this variation have received much attention, but how reproductive costs may influence the timing of subsequent breeding has been largely unexplored. We examined a population of northern wheatears Oenanthe oenanthe to compare three groups of individuals that differed in their timing of breeding termination and reproductive effort to investigate how these factors may carry over to influence reproductive timing and reproductive output in the following season. Compared to females that bred successfully, females that put in less effort and terminated breeding early due to nest failure tended to arrive and breed earlier in year 2 (mean advancement = 2.2 and 3.3 d respectively). Females that spent potentially more effort and terminated breeding later due to production of a replacement clutch after nest failure, arrived later than other females in year 2. Reproductive output (number of fledglings) in year 2 differed between the three groups as a result of group‐level differences in the timing of breeding in combination with the general seasonal decline in reproductive output. Our study shows that the main cost of reproduction was apparent in the timing of arrival and breeding in this migratory species. Hence, reproductive costs can arise through altered timing of breeding since future reproductive success (including adult survival) is often dependent on the timing of breeding in seasonal systems.     

Breeding performance and timing of breeding of inland and coastal breeding Cormorants Phalacrocorax carbo in England and Wales

Capsule Breeding performance was higher at inland colonies than on the coast due to higher nestling survival during late development.

Aims To compare breeding performance of inland and coastal breeding Cormorants in England and Wales and to provide breeding performance data for Cormorants for future demographic studies.

Methods Breeding performance and timing of breeding was monitored at six inland and four coastal colonies during 1997 and 1998. We compare clutch and brood size and egg and nestling survival.

Results Breeding performance was higher at inland colonies because of higher nestling survival during the later stages of nestling development, from 15–56 days.

Conclusions Greater and earlier food availability at inland colonies, resulting in earlier and more protracted breeding is the most probable explanation for differences in breeding performance. A more protracted breeding season would reduce competition for food and enhance breeding performance, which may be especially apparent during late chick development when energy demands are greatest.     

The role of photoperiodism in the seasonal breeding of tropical African ungulates

Records of ungulate calving peaks, from different latitudes within the African tropics, are reviewed. Converting these peaks to conception dates, and plotting them against latitude, reveals whether the initiation of conception may be connected with a photoperiodic response. The north-south plots of a short-day species should lie in diagonally-opposed quadrants, and those of long-day species in the opposite quadrants. The analysis suggests that a photoperiodic stimulus could be a factor initiating conception in some species, but others lack any apparent relationship.     

Protandrous arrival timing to breeding areas: a review

Protandry, the earlier arrival of males to breeding areas than females, is a common pattern of sex-biased timing in many animal taxa (e.g. some insects, fish, amphibians, reptiles, birds and mammals). The adaptive significance of protandry is not fully understood and, since the 1970s, at least seven hypotheses for protandry have been proposed. We describe each of these hypotheses and summarize what is known about each. In three of these hypotheses, the relative arrival timing of males and females has no direct fitness consequences for males or females, but selection for different timing in each sex indirectly produces protandry. In the other four hypotheses, the difference between male and female timing has fitness consequences for males or females and selection directly maintains the fitness-maximizing degree of sex-biased timing. The hypotheses are not mutually exclusive, and the degree of multiple mating by males and the occurrence of male territoriality seem to determine the relative importance of each hypothesis. In order to understand the adaptive significance of sex-biased timing, future studies need to consider all the alternatives and to assess the costs and benefits to males of early arrival relative to calendar date, to other males and to females.     

The influence of food on time budgets and timing of breeding of the Dunnock Prunella modularis

In two years, we provided some female Dunnocks with extra food from January through to July. In one year fed females bred ten days earlier than controls and in another year they bred 22 days earlier, but in neither year did they lay larger clutches. Matched comparisons of the same females on the same territories, who had food in one year but not in the other, showed the same effects. Within both feeder and control females, the earliest breeders were those which had spent more time perching in late winter. Perching time may be a good measure of the time an individual has available above that needed for self maintenance. Therefore females who spent more time perching may have been those first able to cross the threshold of extra time needed for the start of breeding activities.     

Age at first breeding of the African Penguin

Numbers of breeding pairs of African Black Oystercatchers showed a highly significant increase at Cape Agulhas over a 24year study period. Mean numbers of fledglings per pair did not increase correspondingly but showed a cyclic tendency, peaking twice, with a slight overall decline. The increase in the frequency of repeat clutches was close to significant. Nest failures were ascribed largely to human disturbance. Indications of increasing public awareness about the sensitivity of breeding oystercatchers were noted as well as increasing adaptability to human presence among some birds, whereas other birds moved their nests further away from this disturbance. In view of the closure of the Overberg coast to recreational vehicles from 20 February 2002 and the relative importance of the area for the conservation of oystercatchers, this long-term study represents an important baseline against which to measure change.