Pierre Jouventin

Population dynamics of wandering albatross Diomedea exulans and Amsterdam albatross D. amsterdamensis in the Indian Ocean and their relationships with long-line fisheries: Conservation implications

Abstract Studies carried out over the past three decades at Crozet and Kerguelen Islands in the Indian Ocean indicate that wandering albatross Diomedea exulans populations declined markedly, but since 1986 have shown slow recovery. The population of the endangered Amsterdam albatross Diomedea amsterdamensis appears to have similarly recovered since 1985, but remains close to extinction. A demographic study of the Crozet population indicates that the earlier decline was mainly the result of increased adult mortality, and secondarily of low recruitment. Satellite tracking studies of breeding birds and band recoveries of non-breeding birds indicate that during and outside the breeding season these populations are in contact with long-line fisheries, mainly the pelagic Japanese southern blue-fin tuna Thunnus maccoyii fishery and to a lesser extent the Patagonian tooth-fish Dissostichus eleginoides fishery operating on the Kerguelen shelf. Decreased fishing effort and a concentration outside the central Indian Ocean by the Japanese fishery during recent years has probably resulted in the slow recovery of these albatross populations as a result of improved adult survival and recruitment. Long-line fisheries still represent a major threat to great albatross populations, most of which are still declining in the Southern Ocean. Possible conservation measures to reduce mortality in the fishery and to reduce contacts between fishing units and foraging albatrosses are examined.

Population Dynamics of the Wandering Albatross, Diomedea exulans, of the Crozet Islands: Causes and Consequences of the Population Decline

Between 1966 and 1985 breeding populations of wandering albatrosses on three islands of the Crozet group decreased at annual rates of 2.6, 4.9 and 6%, but with a rapid decline, at all except one colony, between 1969 and 1975. For the whole study period, the mean age at first breeding was 11.2 yr in females and 12.1 yr in males. Since 1973 birds have bred at younger ages. Breeding success did not vary significantly over time but was correlated with the survival of breeding birds; it was the same for experienced breeders and for birds attempting a first breeding. Adult survival was 90.5% per year during the rapid decline period and 94.4% afterwards. Females appeared to have a higher mortality than males. Immature survival was low (71.5% per year between fledging and 5 yr old) but increased from 1966 to 1980: it was 91.8% per year between ages 6-11 yr. The high adult mortality appears to be the major cause of population decline and is assumed to result from accidental deaths in fishing tackle and from deliberate trapping or shooting by fishermen. Differential survival between males and females is probably due to their distribution when at sea, females foraging more frequently than males in waters where fishing activities occur. Likewise, immatures foraging in similar waters to females have suffered a high mortality. The consequences of the decline for the future of albatross populations in the southern hemisphere is discussed.

Finding a parent in a king penguin colony: the acoustic system of individual recognition

To be fed, a king penguin, Aptenodytes patagonicus, chick must identify the call of its parents, in the continuous background noise of the colony. To study this recognition process, we played back to the chicks parental calls with acoustic parameters modified in the temporal and frequency domains. The parental call is composed of syllables (complex sounds with harmonic series) separated by pronounced amplitude declines. Our experiments with modified signals indicate that the chicks frequency analysis of the call is not tuned towards precise peak energy values, the signal being recognized even when the carrier frequency was shifted 100 Hz down or 75 Hz up. To recognize the adult, chicks used frequency rather than amplitude modulation, in particular the frequency modulation shape of the syllable. This structure is repeated through the different syllables of the call giving a distinct vocal signature. Our experiments also show that the receiver needs to perceive only a small part of the signal: the first half of the syllable (0.23 s) and the first three harmonics were sufficient to elicit recognition. The small amount of information necessary to understand the message, the high redundancy in the time and frequency domains and the almost infinite possibilities of coding provided by the frequency modulation signature permit the chick to recognize the adult, without the help of a nest site. For these reasons, the code used in the call of the king penguin can be regarded as a functional code, increasing the possibility of individual recognition in an acoustically constraining environment. Copyright 1999 The Association for the Study of Animal Behaviour.

Body Condition and Seabird Reproductive Performance: A Study of Three Petrel Species

We investigated relationships between body condition (body mass scaled by body size) early in the breeding season and reproductive performance of three seabird species showing various life history traits. The study was conducted at Kerguelen Island from 1987 to 1994 on the Blue Petrel (Halobaena caerulea, an oceanic feeder), the Thin- billed Prion (Pachyptila belcheri, a neritic feeder), and the Common Diving Petrel (Pe- lecanoides urinatrix, a coastal feeder). Breeding success was highly variable among years in the three species, but the proportion of nonbreeding experienced breeders varied sig- nificantly only in the Blue Petrel. In the three species, body condition showed considerable year-to-year variation, suggesting substantial fluctuation in the availability of prey early in the breeding season. Relationships between early body condition and reproductive perfor- mance differed among the species. Reproductive success was significantly influenced by early condition in the Blue Petrel but not in the Thin-billed Prion and the Common Diving Petrel. In the long-lived Blue Petrel, depletion of body condition early in the breeding season resulted in a high proportion of nonbreeders and massive egg desertion. On the other hand, the shorter lived Thin-billed Prion and Common Diving Petrel seemed to respond by maintaining their reproductive output during poor years, probably investing more in the reproductive episode. Such contrasted patterns are analyzed in the light of reproductive effort and optimal clutch size theory.

How to vocally identify kin in a crowd: The penguin model

Summary On penguins, individual recognition is observed between mates and between parents and chick(s). During the past five years, their particular strategies of coding—decoding have been tested by playing back modified display calls to six species, in Australia (little penguin, Eudyptula minor ), in Antarctica (Adelie penguin, Pygoscelis adeliae ; emperor penguin, Aptenodytes forsteri ), and in subantarctic islands (king penguin, Aptenodytes patagonicus ; macaroni penguin, Eudyptes chrysolophus ; gentoo penguin, Pygoscelis papua ). All species use only vocal cues to identify their partner, but in territorial species the nest is used as a meeting point. In large species, such as the king and the emperor penguins, which do not have a nest, the brooder carries the egg or the small chick on the feet, while the mate, and then the chick, has to be located in the noisy colony without any topographical cue. According to theory, to extract a signal from background calls, animals analyze either frequency bands or modulations (amplitude and frequency modulations) of the partners call. The first coding-decoding system, used by nesting penguins, is easy to produce but costly in terms of analysis time. The second one, used by nonnesting penguins, is a vocal signature which is fast to analyze but costly to produce. This acoustic signal is particularly efficient as a means to locate immediately the partner on the move in a noisy crowd. Briefly, frequency analysis is enough to solve the relatively easy problem of individual recognition in nesting birds, while the complex temporal analysis of modulations of the two nonnesting penguins is an adaptation to extreme acoustic and breeding conditions. The macaroni penguin, which we have begun to test, seems to use both a frequency code similar to that of the other nesting species and a temporal code close to the one of a nonnesting penguin species, but much simpler.

Cocktail-party effect in king penguin colonies

The king penguin, Aptenodytes patagonicus, breeds without a nest in colonies of several thousands of birds. To be fed, the chick must recognize the parents in a particularly noisy environment using only vocal cues. The call an adult makes when seeking the chick is emitted at a high amplitude level. Nevertheless, it is transmitted in a colonial context involving the noise generated by the colony and the screening effect of the bodies, both factors reducing the signal–to–noise ratio. In addition, the adult call is masked by a background noise with similar amplitude and spectral and temporal characteristics, enhancing the difficulty for the chick in finding its parents. We calculate that the maximum distance from the caller at which its signal can be differentiated from the background noise (signal–to–noise ratio equal to 1) should not exceed 8–9 m in a feeding area. But our tests show that, in fact, chicks can discriminate between the parental call and calls from other adults at a greater distance, even when call intensity is well below that of the noise of simultaneous calls produced by other adults. This capacity to perceive and extract the call of the parent from the ambient noise and particularly from the calls of other adults, termed the ‘cocktail–party effect’ in speech intelligibility tests, enhances the chicks ability to find its parents.

How do king penguins (Aptenodytes patagonicus apply the mathematical theory of information to communicate in windy conditions

In the king penguin (Aptenodytes patagonicus), both pair members alternate in incubating and rearing their chick. Mates can recognize each other among thousands of other birds in the hubbub of the colony using only acoustic signalling: the display call. Large penguin colonies are found on sub–Antarctic islands where strong winds blow throughout the year. We have shown by experiments under natural conditions that the level of background noise increases in windy conditions and thus leads to a diminution of the signal–to–noise ratio. Moreover the emergence level of the signal revealed by entropy calculation is statistically weaker in windy conditions. To achieve breeding success, birds must continue communicating in spite of the significant decrease in the total amount of information that can be transmitted in windy situations. For the first time, to our knowledge, we have shown that a bird species takes into account the constraints imposed by wind on their acoustic communication. In windy conditions, birds try to maintain the efficiency of communication by increasing both the number of calls emitted and the number of syllables per call. This result conforms with predictions from the mathematical theory of communication: increased redundancy in a signal improves the probability of receiving a message in a noisy channel.

High annual variability in reproductive success and survival of an Antarctic seabird, the snow petrel Pagodroma nivea

Demographic parameters were estimated for snow petrels Pagodroma nivea nesting at Pointe Géologie Archipelago, Adélie Land, Antarctica between 1963 and 1990; 21 years of data on adult survival and 27 years of data on breeding success are available. The average age of first return and first breeding were 8.1 and 9.9 years respectively and there was no signifcant difference between the sexes. The overall breeding success averaged 51.3% and was very variable between years (21–80%). Breeding failure was mostly due to incubation failure and annual breeding success was negatively correlated with average snow falls in October–November and October–March. Breeding frequency was very low, averaging 52% of seasons during a reproductive lifetime. Good quality sites, with high occupancy rate and high breeding success were few in the study plots. Poor years in 1966–1967, 1976–1977 and 1983–1984, with low breeding success, very low proportions of nets with breeding attempts and high numbers of non-breeders, occurred 1 year after large-scale El Niño Southern Oscillation (ENSO) events. Snow petrels exhibited very low philopatry. Only 45 birds have been recovered in the study plots from a total of 1115 banded fledglings giving an estimated rate of return of 12.9% between fledging and 3 years old. Annual survival between 3 and 10 years was 91.4%. Annual adult survival (93.4%), though variable, was low during poor years of 1977–1978 and 1983–1984. Adult survival of males (94.7%) was not significantly different from that of females (93.9%). Over the study period, the population of Pointe Géologie was stable. Using the estimated parameters, a Leslie model gave a growth rate of 0.948%, which was probably compensated by immigration (5.7% per year). Restricted numbers of good-quality sites at the place of birth could have led young birds to prospect other colonies and could have selected low philopatry. High adult survival, strong site tenacity and capacity to spread breeding over a long lifetime are probably part of the adaptive strategy of this small fulmarine petrel facing highly variable environmental conditions.

Penguins use the two-voice system to recognize each other

The sound–producing structure in birds is the syrinx, which is usually a two–part organ located at the junction of the bronchi. As each branch of the syrinx produces sound independently, many birds have two acoustic sources. Thirty years ago, we had anatomical, physiological and acoustical evidence of this twovoice phenomenon but no function was known. In songbirds, often these two voices with their respective harmonics are not activated simultaneously but they are obvious in large penguins and generate a beat pattern which varies between individuals. The emperor penguin breeds during the Antarctic winter, incubating and carrying its egg on its feet. Without the topographical cue of a nest, birds identify each other only by vocal means when switching duties during incubation or chick rearing. To test whether the twovoice system contains the identity code, we played back the modified call of their mate to both adults and also the modified call of their parents to chicks. Both the adults and the chicks replied to controls (two voices) but not to modified signals (one voice being experimentally suppressed). Our experiments demonstrate that the beat generated by the interaction of these two fundamental frequencies conveys information about individual identity and also propagates well through obstacles, being robust to sound degradation through the medium of bodies in a penguin colony. The two–voice structure is also clear in the call of other birds such as the king penguin, another non–nesting species, but not in the 14 other nesting penguins. We concluded that the two–voice phenomenon functions as an individual recognition system in species using few if any landmarks to meet. In penguins, this coding process, increasing the call complexity and resisting sound degradation, has evolved in parallel with the loss of territoriality.

Mother-lamb acoustic recognition in sheep: a frequency coding

Ewes of the domestic sheep ( Ovis aries ) display selective maternal investment by restricting care to their own offspring and rejecting alien young. This trait relies on individual recognition processes between ewes and lambs. Whereas identification at the udder is only olfactory, distance recognition is performed through visual and acoustic cues. We studied the effectiveness and modalities of mutual acoustic recognition between ewes and lambs by spectrographic analysis of their vocal signatures and by playbacks of modified calls in the field. Our results show that ewes and their lambs can recognize each other based solely on their calls. The coding of identity within the vocal signatures, previously unknown in sheep, is similar in lamb and ewe: it uses the mean frequency and the spectral energy distribution of the call, namely the timbre of the call. These results point out a simple signature system in sheep that uses only the frequency domain. This engenders a signal with low information content, as opposed to some highly social birds and mammal species that may integrate information both in the temporal and spectral domains. The simplicity of this system is linked to the roles played by vision and olfaction that corroborate the information brought by the vocal signature.