Individual breeding decisions and long-term reproductive strategy in the King Penguin Aptenodytes patagonicus

Although studied for 35 years, knowledge of the reproductive biology of the King Penguin Aptenodytes patagonicus remains incomplete. The chick requires more than 12 months of care, which extends the breeding cycle, including moult, to more than one year, i.e. the King Penguin is neither annual nor biennial. In an attempt to resolve ambiguities in the literature and to elucidate the long-term breeding strategy of the species, we studied breeciing frequency at the individual level, considering the decision to breed in relation to breeding history over the previous few years. Although adult birds attempted to breed annually (0.83 breeding attempts per year), successful rearing occurred, at best, every two years only (maximum of 0.41 fledged chick per pair). Comparing successive years, the number of breeding birds in the colony was stable but the number of fledged chicks varied from 29 to 278 over eight years. These results suggest that King Penguins adopt (as individuals) an opportunistic reproductive strategy, in that they usually lay an egg every year, even when failure is certain. Nevertheless, the decision to breed was not entirely blind, and we identified groups of birds that invested differentially in breeding attempts. The decision to breed was related to the previous breeding frequency, i.e. 81% of the birds that had bred continuously in the past started a new breeding attempt, but only 67% of birds that had missed a year did so. In intermittent breeders, birds that had bred frequently, more often started a new breeding attempt than birds that had largely missed years (71% versus 57%, respectively). Classes of breeders could correspond to age classes, to birds of different breeding quality or to alternative breeding strategies coexisting in the species. Testing the hypothesis that reproductive effort increases with age should be possible in future.     

Interrelationships between breeding frequency,timing and outcome in King Penguins Aptenodytes patagonicus: are King Penguins biennial breeders?

King Penguin Aptenodytes patagonicus chick growth is interrupted by a winter fast which extends the length of the breeding cycle (laying to chick independence) to 14–16 months, so that continuous annual successful breeding appears to be impossible. The 3–month laying period imposes further constraints with respect to timing of breeding attempts in relation to the onset of fasting. By the frequent resighting of individually marked birds at Marion Island, we examined the frequency of breeding and the relationships between timing, outcome and frequency in the same and in consecutive years. A total of 3101 adult King Penguins were banded between 1984 and 1991, yielding continuous breeding histories spanning a maximum of 5 years. Most penguins attempted to breed in consecutive years, although the likelihood of taking a year off increased with the number of consecutive attempts. In any one season, about 19% of potentially breeding adults did not breed. Early breeders were more likely to succeed than late breeders and comprised 84% of breeding attempts of known timing. Successful birds in one season usually bred late in the following season, whereas failed attempts were usually followed by an early attempt. Non-breeding was more likely to occur after a successful outcome than a failed one, and after a year off 93% of birds bred early. It is incorrect to refer to the King Penguin as a biennial breeder.     

Senescence and carryover effects of reproductive performance influence migration,condition, and breeding propensity in a small shorebird

Breeding propensity, the probability that an animal will attempt to breed each year, is perhaps the least understood demographic process influencing annual fecundity. Breeding propensity is ecologically complex, as associations among a variety of intrinsic and extrinsic factors may interact to affect an animal's breeding decisions. Individuals that opt not to breed can be more difficult to detect than breeders, which can (1) lead to difficulty in estimation of breeding propensity, and (2) bias other demographic parameters. We studied the effects of sex, age, and population reproductive success on the survival and breeding propensity of a migratory shorebird, the piping plover (Charadrius melodus ), nesting on the Missouri River. We used a robust design Barker model to estimate true survival and breeding propensity and found survival decreased as birds aged and did so more quickly for males than females. Monthly survival during the breeding season was lower than during migration or the nonbreeding season. Males were less likely to skip breeding (range: 1–17%) than females (range: 3–26%; β_sex = ?0.21, 95% CI: ?0.38 to ?0.21), and both sexes were less likely to return to the breeding grounds following a year of high reproductive success. Birds that returned in a year following relatively high population‐wide reproductive output were in poorer condition than following a year with lower reproductive output. Younger adult birds and females were more likely to migrate from the breeding area earlier than older birds and males; however, all birds stayed on the breeding grounds longer when nest survival was low, presumably because of renesting attempts. Piping plovers used a variety of environmental and demographic cues to inform their reproduction, employing strategies that could maximize fitness on average. Our results support the “disposable soma” theory of aging and follow with predictions from life history theory, exhibiting the intimate connections among the core ecological concepts of senescence, carryover effects, and life history.     

THE BIOLOGY OF OYSTERCATCHERS HAEMATOPUS OSTRALEGUS ON SKOKHOLM ISLAND, S. WALES

A population of about 50 pairs of Oystercatchers Haematopus ostralegus nesting on Skokholm Island, S. Wales, was studied between 1963 and 1965. Other information on Skokholm Oyster-catchers over the last 25 years was also analysed.
The adults were trapped, colour-banded and sexed by bill measurements. With few exceptions, birds kept the same mates and territories from one season to the next. Apparently the male is responsible for retaining the territory. Some Oystercatchers breed at three years but most do not do so until four or five. It seems that there is a high population pressure, preventing young birds from establishing themselves. The annual adult survival in the two years was 88% and 90% respectively.
The average clutch-size on Skokholm is known for many years, and varied annually between 2^.5 and 3.3. The number of c/4 varied greatly from year to year. There was a seasonal decline in mean clutch-size and also in egg and nest success. Predation, especially by Lesser Black-backed Gulls, was the main cause of egg loss.
In 1963, 36.7% of hatched chicks fledged and 59% in 1964. The larger clutches were more successful and produced more surviving young than did the more numerous smaller clutches. Early hatched young are more successful than later young.
The average yearly mortality of birds between fledging and breeding was 40%.     

Population dynamics in a long-lived seabird: I. Impact of breeding activity on survival and breeding probability in unbanded king penguins

Understanding the trade-off between current reproductive effort, future survival and future breeding attempts is crucial for demographic analyses and life history studies. We investigated this trade-off in a population of king penguins (Aptenodytes patagonicus) marked individually with transponders using multistate capture-recapture models. This colonial seabird species has a low annual proportion of non-breeders (13%), despite a breeding cycle which lasts over 1 year. To draw inferences about the consequences of non-breeding, we tested for an effect of reproductive activity on survival and on the probability of subsequent breeding. We found that birds non-breeding in year t show the same survival rate as breeders (two-states analysis: breeding and non-breeding). However, breeders had a lower probability of breeding again the following year. This negative phenotypic correlation suggests the existence of reproductive costs affecting future breeding probability, but it might also be strengthened by late arrival for courtship in year t. A three-state analysis including breeding success revealed that failed breeders in year t have a lower probability to reproduce successfully in year t + 1 than non-breeders in year t, providing some evidence for the existence of reproductive costs. Moreover, successful breeders showed higher survival probability. This positive phenotypic correlation between current reproduction and subsequent survival supports the hypothesis of an heterogeneity in individual quality. Males breeding in year t had a lower probability to breed again in year t + 1 than females, suggesting higher reproductive costs for this sex. Such additional costs might be due to higher male parental investment in the final phase of chick-rearing, which also delays the arrival of males in year t + 1, and decreases their breeding probability. Our study is the first to explore the breeding biology and the demography of penguins without the disturbance of flipper-bands.     

Influence of reproductive success on breeding frequency in four southern petrels

Patterns of breeding frequency of White-headed Pterodroma lessoni, Great-winged Pterodroma macroptera, White-chinned Procellaria aequinoctialis and Grey Petrels Proceharia cinerea have been studied at Kerguelen and Crozet Islands. The White-headed Petrel (summer breeder) followed an essentially biennial cycle with only 13% of successful individuals breeding again the next year. On the other hand, the Great-winged Petrel (winter breeder) was mainly an annual breeder with 78% of successful birds breeding again the next year. Both White-chinned (summer breeder) and Grey Petrels (winter breeder) showed a higher breeding frequency than Pterodroma species, with 91% and 93%, respectively, of successful birds returning to breed the following season. These contrasting patterns may be related to the timing of energetic constraints encountered during the interbreeding period, principally the moult and the restoration of breeding condition. It is suggested that these post-breeding constraints are more marked in winter and in oceanic waters, leading to breeding frequencies being lower than in summer and in neritic waters. The intermediate patterns of breeding frequency found in the Great-winged Petrel (mainly annual) and the White-headed Petrel (mainly biennial) show that among Procellariiformes there is a continuum between annual and strictly biennial species.     

Annual cycles in Jamaican forest birds

The annual cycles of forest birds in Jamaica were found to be very similar to those at higher latitudes. Most species bred between March and September, though a few possibly breed throughout the year, especially in cultivated areas. Primary moult followed immediately after breeding, and in some species was apparently arrested to allow a further breeding attempt. Several species were fatter outside the breeding season than during it, and this is interpreted as "winter fattening" comparable to that found in many birds at higher latitudes. Weights varied little but individuals retrapped were usually heavier outside the breeding season. In some species the first complete moult took place at the end of the first year, implying that the birds do not breed until at least two years old.     

Breeding site fidelity and natal philopatry in the Redshank Tringa totanus

This paper presents the results of a study carried out on breeding Redshank in the Ribble Marshes, Lancashire, England.
Redshank tend to return to the same breeding area year after year. There was no detectable sex bias in return rates. Experienced birds were more site faithful than inexperienced birds, with previously successful birds exhibiting the highest degree of breeding site fidelity. Older, more experienced birds were more successful at hatching eggs than inexperienced birds.
Breeding dispersal was the same both within and between years. Faithful pairs and males nesting with a new mate dispersed significantly shorter distances than females nesting with a new partner. Dispersal distances in female Redshank were affected by breeding success: unsuccessful females, nesting with a new mate, dispersed significantly farther than successful females. A pair's breeding success influenced the following year's mate fidelity. However, other factors such as overwintering survival and date of return may also have influenced mate fidelity.
Redshank were highly faithful to their natal area; a high proportion of birds that survived post-fledging mortality returned to breed in their area of birth. No sex bias in natal dispersal was detected. Approximately 50% of Redshank breed in their first year of life.     

FACTORS AFFECTING THE AGE OF FIRST BREEDING OF THE KITTIWAKE RISSA TRIDACTYLA

At a Kittiwake colony in Northumberland, 80% of those birds which returned to their natal colony to breed were males and these supplied 52% of all male recruits. More females breed away from their natal colony than males. There was no differences in the proportions of young fledged from sites in the centre or at the edge of the colony, or by parents of different experience, which returned to breed. Kittiwakes breed for the first time at ages from 3 to 8 years, but most at 4 or S years old. Males arrive back at the colony at an earlier age than females and breed for the first time one year earlier. Males obtaining sites at the centre of the colony first breed at an earlier age than those at the edges. Neither the age nor the area of first breeding appear to be transmitted from parent to offspring. Males breeding first aged 4 years or younger produced more young than those which first bred aged 5 years or older, despite their partners laying smaller clutches. This difference was most marked among those males recruited to sites in the centre of the colony. The advantage of this earlier breeding is counteracted by a lower survival rate among those males which start to breed at the younger ages. In all breeding Kittiwakes, annual reproductive output increases with experience while annual survival rates decrease. Once they had started to breed, many birds failed to breed in one subsequent season. Nearly 60% of these cases of intermittent breeding occurred in the year following first breeding. Intermittent breeding was most frequent among young birds and among females. It is suggested that each breeding involves a cost to the individual in terms of reduced survival, and that deferred and intermittent breeding are means of guarding survival. A model is proposed whereby the age at which a bird starts to breed, the nesting site which it obtains, and its subsequent breeding strategy result in each individual producing an optimal number of reproducing offspring in its lifetime, relative to its quality.     

Life-history variations of the Lesser Sheathbill Chionis minor in contrasting habitats

From 1987 until 1995, life-history traits of the Lesser Sheathbill Chionis minor in the Kerguelen Archipelago were compared with those at other localities, where this species breeds in seabird colonies. At Kerguelen Island only, some pairs breed on shores free of penguin and cormorant colonies. Moreover, pairs, including nonbreeders, and solitary individuals maintain territories all the year round. Site and mate changes were not linked, and all divorces were permanent. Fidelity rates were similar in all localities and so were the annual survival rates of adults. The survival rate of immature individuals was highest at Kerguelen Island, where sheathbills laid smaller clutches, produced fewer fledglings and had lower breeding success than in the other islands. At Kerguelen Island, pairs breeding on shores had similar clutch sizes but fledged fewer offspring than those breeding in seabird colonies. Further, the proportion of vacant territories and nonbreeders was higher on shores. Kerguelen sheathbills devoted less time to food acquisition than those on Marion Island, being exceptionally kleptoparasitic, and spent a smaller part of their foraging time exploiting seabird colonies. Their diet was mainly algae. The differences on Kerguelen Island as compared with other localities were caused by the presence of an extensive intertidal zone on the former, which reduced competition, making many more sites suitable and the environment more predictable. These life-history and behavioural traits are discussed in relation to life-history theory. As differences were also found, although less extensive, within the Kerguelen Archipelago, we suggest that some traits represent an adaptive response to external constraints and that the life-history strategy of the Lesser Sheathbill is particularly opportunistic.     

Seasonal changes in age class structure and reproductive status of house mice on Marion Island (sub-Antarctic)

Feral house mice on sub-Antarctic Marion Island become reproductively active (males scrotal, females with perforate vaginas or pregnant) at an age >60 days and breed until death, which may occur at more than 13 months. Breeding is strongly seasonal; pregnant or lactating females were found only from October to May. A substantial proportion of mice old enough to breed in one summer overwinters to form a significant component of the breeding population the following summer but it is unlikely that any survive a second winter. The onset of breeding is closely synchronized with increasing day length but occurs about 2 months before mean temperature at the ground surface starts to increase significantly. Cessation of breeding is more closely associated with declining temperatures in late summer. For both males and females, the best correlation between reproductive activity and any of the temperature parameters measured was with average maximum temperature 1 cm above the ground. Competition for macroinvertebrate prey increases sharply in early winter due to high mouse numbers. The breeding season in 1991/1992 and 1992/1993 was at least 2 months longer than in 1979/1980, because the mice started breeding earlier, and stopped breeding later, in 1991/1993. The later cessation of breeding in 1991/1993 was despite the fact that there was a greater competition for macroinvertebrate prey, and that mean air temperatures during the early winter months were lower, than in 1979/1980.     

Why breed every other year? The case of albatrosses.

Albatrosses exhibit extremely low reproductive rates, each pair brooding only one egg and subsequent chick at a time. Furthermore, in several of the species, the majority of successful pairs breed only once every second year (termed 'biennial' breeding). Thus, on average, these latter species have an annual fecundity of about half an offspring per year, while other albatrosses produce an egg and chick every year. Using our 40-year bank of demographic data, we compared 12 species of albatrosses according to these two breeding strategies to examine potential causes of biennial breeding. Biennial breeding could be due to physiological constraints, larger animals breeding more slowly, or ecological constraints, more distant pelagic feeding trips being energetically costly, or both. We tested these hypotheses by looking for predicted associations between the duration of the rearing period, the distance to the oceanic feeding zone and breeding frequency. We also looked for associations of these variables with other life-history traits. Body size had a strong influence on the duration of the rearing period, but not on the distance that birds travelled to the feeding zone. Both the duration of the rearing period and distance to the feeding zone appeared to have direct influences on breeding frequency, as revealed by a path analysis, and thus both hypotheses to explain biennial breeding were supported. Finally, breeding frequency exhibited a strong trade-off with adult survival and age at maturity, indicating that slower breeders live through more breeding seasons, perhaps mitigating their lower annual reproductive output.     

The effects of background mortality on optimal reproduction in a seasonal environment

We consider optimal annual routines of reproductive behaviour in a seasonal environment. In our model the condition of the organism is adversely affected by hard work, but can recover during easy periods. Our analysis concentrates on the effects of background mortality (i.e., mortality that cannot be avoided) on the optimal strategy and how often an organism following this strategy breeds. In particular, we are concerned with whether reproduction occurs at specific times of year (entrained to the annual cycle), and if so then how many reproductive bouts occur per year. We find that an increase in background mortality can have various effects. If the animal is entrained to the annual cycle and has one breeding attempt per year, then breeding tends to occur earlier and there may be two breeding attempts per season. Another possible outcome is that breeding is no longer entrained. If the animal is entrained but sometimes skips reproduction so that it does not breed every year, then an increase in mortality may make it more likely that the animal breeds every year. We show that as background mortality increases the resultant increase in the frequency of breeding contributes to the increase in annual mortality. We also explore the effects of mortality on the timing of reproduction within a year, highlighting the tension between the interests of the parent and that of the young.     

The endocrine basis of the reproductive cycle in the king penguin (Aptenodytes patagonicus)

What is the breeding frequency of the king penguin? More than 30 years of study and five major investigations, did not answer this question owing to the length (14 months) and the spreading (four months of laying) of reproductive events.
Following intensively during three consecutive years nearly 1000 tagged birds in a small colony, we obtained the individual history of a large part of the population. To these demographic and phenological studies, we have associated an endocrinological study validating blood samples and experiments in another colony.
The success or failure of a breeding cycle determines the timing of the subsequent breeding attempt. At Crozet Islands, the king penguin can rear one chick every two years at best: a successful breeding is followed by unsuccessful late breeding (or by non-breeding). So a large part of the population displays an annual periodicity of breeding attempts but with low individual breeding success.
The restarting of the reproductive cycle appears basically to be annual, the pituitary responding to the photoperiod. Steroid patterns present classical variations of level according to the reproductive stage. Prolactin (PRL) and luteinizing hormone (LH) are antagonists but, in this species, PRL remains high without external stimulation. To relay after failure in the field. we have experimentally to break down endogenous PRL. So, we have demonstrated that PRL has a key role in the reproductive cycle.
Paradoxically, the king penguin is an irregular breeder, quasi-biennial, although physiologically an annual breeder. In winter, there is not enough food at sea to rear the chick and during four months, the chick fasts. So a successful breeding cycle, which can be shortened to only nine months in captivity, is extended to more than a year for ecological reasons.     

Annual productivity and individual female reproductive success in a Great Bustard Otis tarda population

The reproductive success of Great Bustards Otis tarda in north-western Spain was studied between 1987 and 1998, both at the population ( c . 700 adult females breeding in our study area) and the individual level (sample of 32 marked females). Overall productivity was low, with a population mean of only 0.14 chicks reared per adult female, and an average breeding success of 0.15 chicks per year in the sample of marked females, but interannual variability was high (0.04–0.29). Population productivity was positively correlated with winter (October–March) precipitation prior to each breeding season, and negatively correlated with the number of days of rain during the hatching period. High annual productivity resulted from a high proportion of females rearing two chicks. Reproductive success was higher in females older than 6 years than in younger birds. The proportion of females in the marked sample that failed in breeding after having bred successfully the previous season was significantly higher than the proportion of those that did not. Finally, females with a higher than average breeding success tended to breed successfully in years of both low and high population productivity, whereas those with lower than average breeding success did so only in years of high productivity.     

Density-dependent age at first reproduction in the eastern kingbird

Theory predicts that maximal fitness is obtained by individuals who begin to breed immediately upon reaching sexual maturity. However, delayed breeding occurs regularly in some taxa, and in birds and mammals is most often associated with long lifespan and/or limited access to suitable habitats. Delayed breeding is not expected among relatively short-lived species such as migratory passerine birds, but this assumption remains untested in many species. Here we quantify age at first reproduction in an eastern kingbird Tyrannus tyrannus population breeding in an ecological island, and through both observational and experimental approaches, investigate the potential causes for the high frequency of delayed breeding that occurs in this population. Nearly half of the fledged nestlings that returned to the breeding grounds did not breed in their first potential breeding season. Some non-breeders occupied territories, for at least some period, but most remained as non-territorial 'floaters'. Parentage analysis failed to show any reproductive success for female floaters, and only limited success for male floaters, indicating that floating was not a successful reproductive tactic. On the other hand, a strong negative relationship existed between population size and the proportion of young birds that bred in their first year, and non-territorial birds of both sexes quickly filled territory vacancies created by experimental adult removals. Limited breeding habitat and territorial behavior of older birds thus appear to be the main causes of delayed breeding in kingbirds. The frequency of delayed breeding in most species is unknown but of potential significance because failure to incorporate accurate estimates of age at first reproduction in population models may lead to flawed population projections.     

POPULATION DYNAMICS OF THE FLIGHTLESS CORMORANT NANNOPTERUM HARRISI

A small population of Flightless Cormorants was followed from 1970 to 1975 inclusive. The birds were extremely sedentary, most never moving more than 2 km from where hatched. Many birds bred several times within a year, almost always with different mates. After successful breeding the mean interval to the next attempt among females was significantly shorter than among males, probably because the male continued to attend the juvenile for longer than did the female. There was an annual peak of nesting in April to November, when sea temperatures were lowest; some nesting occurred in other months but these nests were less successful. About 73% of juveniles survived at least three months after going to sea. Adult females had a significantly higher rate of annual survival (91%) than did males (82%). The mean annual survival of both sexes combined over a 13 year period was 87%. The mean age of first breeding was about 30 months for both males and females. In 1972 breeding success (0·14 young fledged per pair) was much lower than in other years (0·60 young per pair), a lower proportion of juveniles survived, no birds bred for the first time and probably many fewer pairs nested. Adult survival was not affected. This reduced breeding output was associated with an influx of anomalously warm sea water to the area (El Niño). The availability of food is probably both the ultimate and the proximate factor controlling the timing of breeding.     

Breeding territory fidelity in a partial migrant, the American dipper Cinclus mexicanus

American dipper Cinclus mexicanus populations are frequently composed of resident individuals that occupy permanent territories year round and migratory individuals that overwinter with residents but migrate to breeding territories on higher elevation creeks each spring. Between 1999 and 2004 we examined how migratory strategy (resident/migratory) and sex differences influence breeding territory fidelity of American dippers occupying the Chilliwack River watershed, British Columbia, Canada. Counter to expectation we found that the migratory strategy of American dippers did not influence whether birds breeding in one year were found on their former breeding territory in the next. Migratory strategy also did not affect the probability that known surviving dippers occupied the same breeding territory in the following year. Males and females were equally likely to be found on their former territory in the following year (females 43%, males 41%) and known survivors had similar levels of breeding territory fidelity (females 74%, males 68%). However, breeding territory fidelity of males and females varied in response to different factors. Surviving female dippers were more likely to be found on their former breeding territory in the subsequent year following a successful breeding attempt than an unsuccessful breeding attempt. Prior reproductive performance did not influence whether surviving male dippers were found on their former breeding territory. Male dippers were more likely to be found on their former territory and, if they survived, have higher breeding territory fidelity when their mate also returned to that same territory. Mate retention also influenced whether females were found on their former territory in the following year but had no effect on the breeding territory fidelity of known survivors. We argue that sex‐specific dispersal decision rules in American dippers are driven by sex differences in the predictability of breeding performance between years and sex differences in how mate retention influences subsequent reproductive success.     

Arrival fat and reproductive performance in a long-distance passerine migrant

Long-distance passerine migrants deposit substantial fat stores to fuel their migratory journey. Many of those migratory birds arrive at their northerly breeding grounds with larger fat stores than were necessary to reach their breeding area. Both male and female American Redstarts ( Setophaga ruticilla) arrived to breed in Michigan's Upper Peninsula with fat, and females arrived with more fat than males in 2 out of 3 years. We test the hypothesis that migrants arriving at the breeding grounds with more body fat have higher reproductive success than birds arriving with little or no fat. Females, and to a lesser extent males, that arrive with fat experience gains in reproductive performance as evidenced by increased clutch size, egg volume, and nestling mass. The results have implications for understanding how events occurring during one phase of the annual cycle influence survival and/or reproductive performance in subsequent phases.