THE SOCIAL ORGANISATION OF BEE-EATERS (MEROPIDAE) AND CO-OPERATIVE BREEDING IN HOT-CLIMATE BIRDS

In the colony-nesting bee-eater Merops bulocki of the northern savannas of Africa males preponderate in the proportion 1 -5 to 1 female, initial breeding occurs at varying ages, and adults of both sexes and all age classes, particularly one-year-old males, assist breeding pairs with nest excavation, incubation, and provisioning the pulli and fledglings. Up to three helpers can occur at one nest, and they may be siblings of a previous year's brood. Pair-bonds are for life, and bonds formed between the breeding pair and their helpers may endure until next season. Some evidence suggests that other gregarious open-country bee-eater species are similar in these respects but that forest and solitary-breeding savanna species have the sex ratio at parity and do not breed co-operatively. Breeding dispersion of savanna species is related to specific size, the largest (which forage most widely) nesting in the densest aggregates. Other instances of birds with comparable social organisations are briefly reviewed. The 80 species involved comprise broad systematic and ecological spectra and about 60 of them inhabit hot climates in America, Africa and Australia. It is suggested that co-operative breeding provides a reserve of experienced individuals whose recruitment to breeding permits (1) fine control of stable populations in non-seasonal habitats (tropical forest) within the capacity of the food resources; (2) crude adjustment of fluctuating populations in habitats with unpredictable rainfall (Australia), enabling them rapidly to recuperate from depression and to achieve the highest population level the improved food resources can sustain; and (3) regulation of populations in intermediate habitats (tropical savannas) by either means according to the dictates of immediate ecological circumstances.     

THE LEVEL OF RESERVE PROTEIN AS THE PROXIMATE FACTOR CONTROLLING THE TIMING OF BREEDING AND CLUTCH-SIZE IN THE RED-BILLED QUELEA QUELEA QUELEA

Changes in the fat and flight muscle protein reserves of adult Red-billed Queleas Quelea quelea were followed in two colonies in Tanzania and Botswana. At the start of a breeding attempt the protein reserves were higher that at any other time of the year, particularly in females which had heavier flight muscles (non-fat dry weight) than did the (larger) males at that time. The pre-breeding increase in the labile component of the muscle protein (the actual protein reserve) is calculated at 80% for females, but only 14% for males. The fat reserve was only increased slightly at the beginning of the breeding attempt.
In both sexes, though for different reasons, the protein and fat reserves fell rapidly during the first few days of the attempt, in some individuals to dangerously low levels. During the incubation period there was rapid recovery while the situation during the rearing period appeared to vary between colonies.
It is proposed that the proximate control of breeding is provided by the individual's own body condition, and particularly the state of its protein reserves. No environmental releasers are required for the birds to breed at the appropriate time of the year.
Individual females producing two, three and four egg clutches differed in the rate at which their reserves fell during egg formation. The results are used to support the view that in this quelea the actual clutch-size produced on any occasion is the largest the female can produce before becoming too enfeebled. Thus, clutch-size appears to be determined phenotypically downward from a maximum which is indirectly under genetic control.     

Segregation in space and time explains the coexistence of two sympatric sub‐Antarctic petrels

Biological communities are shaped by competition between and within species. Competition is often reduced by inter‐ and intraspecific specialization on resources, such as differencet foraging areas or time, allowing similar species to coexist and potentially contributing to reproductive isolation. Here, we examine the simultaneous role of temporal and spatial foraging segregation within and between two sympatric sister species of seabirds, Northern Macronectes halli and Southern Macronectes giganteus Giant Petrels. These species show marked sexual size dimorphism and allochrony (with earlier breeding by Northern Giant Petrels) but this is the first study to test for differences in foraging behaviours and areas across the entire breeding season both between the two species and between the sexes. We tracked males and females of both species in all breeding stages at Bird Island, South Georgia, to test how foraging distribution, behaviour and habitat use vary between and within species in biological time (incubation, brood‐guard or post‐brood stages) and in absolute time (calendar date). Within each breeding stage, both species took trips of comparable duration to similar areas, but due to breeding allochrony they segregated temporally. Northern Giant Petrels had a somewhat smaller foraging range than Southern Giant Petrels, reflecting their greater exploitation of local carrion and probably contributing to their recent higher population growth. Within species, segregation was spatial, with females generally taking longer, more pelagic trips than males, although both sexes of both species showed unexpectedly plastic foraging behaviour. There was little evidence of interspecific differences in habitat use. Thus, in giant petrels, temporal segregation reduces interspecific competition and sexual segregation reduces intraspecific competition. These results demonstrate how both specialization and dynamic changes in foraging strategies at different scales underpin resource division within a community.     

The vocal systems of two nocturnal burrowing petrels, the White-chinned Procellaria aequinoctialis and the Grey P. cinerea

I studied the calls of White-chinned Petrels Procellaria aequinoctialis and Grey Petrels P. cinerea at the Prince Edward Islands in the Southern Ocean. White-chinned Petrels gave two calls. One, the Wheezy call, was usually given from within breeding burrows, was given in response to playback of strange (= non-mate) calls, and probably served a burrow defence function. The other call, the Rattle call, was uttered roughly as often on the ground as from within the burrow. This call was mostly given by males and probably served as sexual advertisement. The one identified call type of the Grey Petrel was given in the same circumstances as the Wheezy call of the White-chinned Petrel.
In both species there was evidence of mate recognition of calls. Birds tended to remain silent to the playback of the mate's call, whereas they responded vocally to strange calls.
This vocal system, where both sexes share two call types but where sexual dimorphism in call is absent, has not been described before for petrels. Possible reasons for the variation in petrel vocal systems are discussed.     

Moult of the giant petrels Macronectes halli and M. giganteus at South Georgia

Moult scores were collected from colour-ringed individuals of known reproductive status of the two species of giant petrel, Macronectes halli and M. giganteus , at Bird Island, South Georgia between 1978–81.
Both species showed a substantial overlap between breeding and wing-moult, unlike most other Southern Ocean seabirds. Males started moult before females and both sexes of M. giganteus moulted at an earlier stage of the breeding cycle than M. halli , which breeds six weeks earlier than its congener.
Changes in moult rate during the breeding season are documented for both species, with Id. halli showing a rapid increase as the chick nears fledging. Male M. giganteus show a notably different pattern to the other three species-sex groups, starting moult much earlier (at egg-laying), with greater individual synchrony and usually suspending primary moult throughout the main chick growth period, whereas only two male M. halli and no females of either species suspended moult. Differences in pattern, timing and rate of moult are interpreted in terms of availability of food resources and the competing energy demands of other activities, especially chick-rearing.
Completion of primary moult could not be observed in the field but was estimated using data frcsm non-breeding birds and failed breeders; the latter started a rapid moult almost immediately they failed. In both sexes of both species moult is probably concluded at least by early winter.
The general pattern of moult in giant petrels at Bird Island is contrasted with that of other populations and species of Southern Ocean seabirds. It is suggested that the unusually extensive overlap between breeding and moult in giant petrels is a consequence of the very abundant and easily available summer food supplies (especially carrion) and the much diminished winter resources, favouring a completion of moult by the beginning of the winter.     

SUBFOSSIL PETREL BONES FROM THE CHATHAM ISLANDS

The breeding community of petrels on the Chatham Islands has previously seemed curiously poor compared to that of analogous stations in the Indian Ocean or South Atlantic (14 species compared with 18 in the Tristan-Gough group). Examination of subfossil deposits from the Chatham Islands probably dating from the early stages of human colonization which occurred within the last few hundred years reveals remains of at least 20 petrels, all of which except one may well have bred in the past, without including storm petrels, of which two species are still known to breed while others may also have bred in the past. The grand total of at least 21 breeding species, many apparently in vast numbers, would probably make the archipelago the most important breeding station for petrels in the world at the time of the first human colonization. It seems possible that in addition to the present breeding species the following may have bred: at least one endemic species of gadfly petrel, the Magenta Petrel Pterodroma magentae , and local populations of at least two other gadfly petrels, two shearwaters of the genus Procellaria and two of the genus Puffinus and a sooty albatross of the genus Phoebetria . Small populations of these, and perhaps other undetected species as well, may still survive in inaccessible places.     

Contrasting effects of tropical cyclones on the annual survival of a pelagic seabird in the Indian Ocean

Tropical cyclones are renowned for their destructive nature and are an important feature of marine and coastal tropical ecosystems. Over the last 40 years, their intensity, frequency and tracks have changed, partly in response to ocean warming, and future predictions indicate that these trends are likely to continue with potential consequences for human populations and coastal ecosystems. However, our understanding of how tropical cyclones currently affect marine biodiversity, and pelagic species in particular, is limited. For seabirds, the impacts of cyclones are known to be detrimental at breeding colonies, but impacts on the annual survival of pelagic adults and juveniles remain largely unexplored and no study has simultaneously explored the direct impacts of cyclones on different life‐history stages across the annual life cycle. We used a 20‐year data set on tropical cyclones in the Indian Ocean, tracking data from 122 Round Island petrels and long‐term capture–mark–recapture data to explore the impacts of tropical cyclones on the survival of adult and juvenile (first year) petrels during both the breeding and migration periods. The tracking data showed that juvenile and adult Round Island petrels utilize the three cyclone regions of the Indian Ocean and were potentially exposed to cyclones for a substantial part of their annual cycle. However, only juvenile petrel survival was affected by cyclone activity; negatively by a strong cyclone in the vicinity of the breeding colony and positively by increasing cyclone activity in the Northern Indian Ocean where they spend the majority of their first year at sea. These contrasting effects raise the intriguing prospect that the projected changes in cyclones under current climate change scenarios may have positive as well as the more commonly perceived negative impacts on marine biodiversity.     

THE BREEDING OF CORY'S SHEARWATER CALONECTRIS DIOMEDEA ON THE SALVAGE ISLANDS

The breeding of Cory's Shearwater on Selvagem Grande was studied during the seasons of 1968 and 1969, on a number of specially timed visits. After a pre-laying exodus (duration not determined) the birds returned in a mass to the island on 26 May 1969 and laying began immediately reaching its peak on 31 May. Egg dimensions and weights are tabulated. In most cases the female handed over to the male immediately after laying, and the two sexes incubated in alternating spells averaging about six days. The incubation period averaged 53-8 days. The chicks reached their maximum weight at about 53 days, but the fledging period was not determined. In 1968 young birds were leaving the nest on 22–25 October, about 90 days after the 1969 mean hatching date. Herring Gulls were important egg predators, but losses of chicks were few, 29 out of a sample of 30 being alive at the age of about 60 days.     

Breeding ecology of the White-headed Petrel Pterodroma lessoni on the Kerguelen Islands

The breeding season of the White-headed Petrel Pterodroma lessoni on Mayes Island off the Kerguelen archipelago was studied between December 1985 and February 1987. The birds returned to land in November, and the chicks hatched at the end of January and fledged in May. These incubation and fledging periods are among the longest known in the family Procellariidae. Successful birds normally bred every two years, which has not previously been reported for any member of this family. The breeding ecology is compared to that of other gadfly petrels from sub-antarctic and tropical waters, and the breeding frequency is discussed.     

FIELD-NOTES ON NIDIFICATION AND DISTRACTION-DISPLAY IN THE GOLDEN PLOVER

Data for the Golden Plover Pluvialis apricaria , breeding in the Faeroe Islands, suggest that the species is more successful up to. and including the hatching phase than the Whimbrel Numenius ph. phœopus. Oyster-catcher Hœmatopus ostralegus occidentalis , and Faeroe Snipe Capella gallinago faeroeensis. Comparative figures for average clutch, young leaving the nest, and losses due to predators, infertility, etc., are given for a small number of nests.
Simultaneous hatching is more general than in the Whimbrel and the hatching-period, normally about 100 hours, is some 10–20 hours less. Detailed records of hatching are given in the case of seven nests.
Field-notes are given on the nuptial flight, and a "partnership-run" is described.
Both sexes share incubation and care of the young, the family quickly deserting the nesting-site. Shell remains are removed and young hatched late in the day appear to pass the night on the nest.
In distraction-display an aggressive form was not recorded, but stationary and moving "lure displays" of three distinct kinds (in addition to the normal run from the nest or young) are described. A case is cited in which the male, when flushed from eggs, directed the "lure-display" at its mate.     

BREEDING BIOLOGY AND BEHAVIOUR OF THE QUAIL FINCH ORTYGOSPIZA ATRICOLUS

Summary

Nuttall, R.J. 1992. Breeding biology and behaviour of the Quail Finch Ortygospiza atricollis. Ostrich 63:110-117.

During a study of the breeding biology of the Quail Finch Ortygospiza atricollis, observations of nest-building, egg-laying, incubation and nestling periods, and nestling development in a grassland near Pietermaritzburg, South Africa were supplemented with observations of breeding behaviour in captivity. Mean clutch size was 4,5 and eggs were laid at intervals of approximately one day. Incubation began after the third or fourth egg was laid. An incubation period of 15–16 days and an estimated nestling period of 18–19 days was recorded. Incubation and brooding are shared by both sexes. Breeding success was low (26,7% ?28,6%), with most losses resulting from predation during either the egg-laying or incubation stages.     

TIMING AND SPACING OF BROODS IN THE BLACK-HEADED GULL LARUS RIDIBUNDUS

The nests of the Black-headed Gull Larus ridibundus are closely aggregated into dense colonies and their use synchronized, these two phenomena together tending to produce a maximal clumping effect. Within such a colony however, nests were found to be spaced out to produce a non-random uniform distribution. The commonest distance between neighbouring nests was found to be about one metre, in contrast to related species. This study was concerned with two aspects of this distribution pattern; its survival value and its behavioural causation.
It was found that pairs nesting just outside the colony had a much lower breeding success than those nesting in the colony and that nests on the colony fringe had a slightly lower success than those in the centre. Pairs laying during the peak laying period had a higher breeding success than pairs laying either earlier or later in the season. Since by far the most important mortality agent was predation, it seems likely that both clustering and synchronization of nesting function as antipredator systems and arguments in favour of this are discussed.
Variations in nest-spacing within the colony were not correlated with variations in breeding success.
In the causation of the spacing between nests, territorial aggression was demonstrated to be an effective dispersion mechanism and the way in which this mechanism works was investigated in detail.
This spacing mechanism was not sufficient by itself to explain the observed densities, which were higher than one would expect from the aggression alone; there was also some tendency for birds establishing a new nest-site to cluster close to others. The interaction between this, the territorial aggression of the residents and the subsequent avoidance responses of the settling birds, can explain the nest spacing pattern and probably also the observed densities.     

Use of burrow entrance flaps to minimise interference to Chatham petrel (

The Chatham petrel (Pterodroma axillaris) is an endangered species, restricted to a single population on South East Island, Chatham Islands. The key threat to breeding success is loss of chicks as a result of interference by broad-billed prions (Pachyptila vittata) prospecting for burrows for their oncoming breeding season. The effectiveness in decreasing interference using an artificial burrow entrance flap was investigated. The flap exploits behavioural differences between the species. Chatham petrels have a high incentive to push through a flap due to their investment in their burrow and chick, while prospecting prions are influenced by ease of access when searching for potential burrows. This trial found 90% of Chatham petrels entered their burrows through the artificial flap. Flaps acted as barriers to broad-billed prions, where 22% entered the burrow through the flap (P <0.01) compared to the control burrows. Artificial burrow flaps have the potential to provide a low cost, low labour strategy for protecting the known breeding population of Chatham petrels.     

GROWTH RATES OF BIRDS IN THE HUMID NEW WORLD TROPICS

The growth curves of 40 species of lowland neotropical birds were fitted by logistic equation. The birds were mostly from Panama, Trinidad and Surinam. The growth constants of the fitted equations (asymptote A and growth rate K) were compared within and among species, and with previously published data on temperate species. Growth parameters of tropical passerines are about as variable within species as they are within temperate species. In both cases, variation in A and K between broods is greater than it is within broods. Panamanian birds breed during the dry-wet transition and conditions for growth apparently improve as rainfall increases. Asymptotes of growth curves are higher, and mortality within broods lower, as the breeding season progresses. Asynchronous hatching and the reduction of brood-size by selective starvation of young is a prominent phenomenon during the early part of the breeding season. Several instances are reported, however, of young persisting in nests with inadequate feeding and greatly subnormal weights. Slowed development under conditions of poor nutrition may be adaptive in the tropics if periods of low food availability are short and allow the possibility of recovery from undernourishment. As a group, neotropical lowland passerines (30 species) grow 23% more slowly than a sample of 51 temperate passerines. Variation of growth rates among these tropical species is similar to variation among temperate species, and it is related to adult body-size the length of the nestling period. Young of tropical and temperate species attain similar asymptotes, relative to adult body-weight, by the end of the nestling period. Hypotheses are advanced which might explain the slower growth rate of tropical species, and tested to the extent available data permits. (1) Because brood-size can be changed only by adding or removing whole young, changes in growth rate could provide finer adjustment of the energy requirements of the young to the feeding capacity of the parents. This model predicts different means and variances for growth rate within groups of species with different clutch-sizes, predictions not supported by available data. (2) Growth rate is shown to increase the maximum energy requirement of a nestling only if K exceeds some value determined by the energy requirement of the young, growth rate should vary in proportion to the level of basal maintenance metabolism. In a small sample of tropical species, rates of basal metabolism were 25% lower than in a comparable sample of temperate species. These data therefore support the hypothesis, although the cause of the lower metabolic rate of the tropical nestlings is not known. (3) Daily periods of hypothermia could reduce the energy requirement of the young and at the same time reduce their growth rate; but observations of body temperatures of tropical nestlings are contrary to this hypothesis. (4) The short day-length of tropical climates reduces the time during which young can assimilate energy relative to their energy expenditures. This model predicts that tropical nestlings would have less productive energy available, (consistent with their reduced growth rates), but it also predicts that arctic birds should grow faster than temperate species, which is not confirmed by available data. (5) The low nitrogen content of fruits may cause the slow growth of a few strictly frugivorous species (Oilbird and Bearded Bellbird), but among other tropical species growth rate is not correlated with the estimated proportion of fruit in the diet.     

Food, feeding ecology and ecological segregation of seabirds at South Georgia

At the sub-Antarctic island of South Georgia 25 of the 29 breeding species are seabirds. Fifteen of these have recently been studied in some detail. By examining the timing of their breeding seasons and their diet and feeding ecology (especially feeding techniques and potential foraging ranges), the nature of their ecological isolating mechanisms, and in particular the way in which they partition the resources of the marine environment, are reviewed.
Although breeding season adaptations occur (winter breeding in Wandering Albatross and King Penguin; out of phase breeding in two species-pairs of small petrels) these are less important than dillerences in food and feeding ecology. There is a fundamental distinction between the niche of pursuit-diving species (mainly penguins) and the remainder which are basically surface-feeders. The two abundant krill-eating penguins show clear differences in feeding zones. Three albatrosses and a petrel feed mainly on squid and there are differences in both the species and size of the prey of each. The remaining seabirds chiefly take krill (although the giant petrels are extensive scavengers and some smaller petrels specialize on copepods) and utilize different feeding methods and areas to do so.
Various adaptations related to inshore and offshore feeding zones are discussed. Although most species possess a combination of ecological isolating mechanisms additional evidence for the particular importance of dietary differences is presented.     

BREEDING BIOLOGY OF THE GREY-FACED PETREL PTERODROMA MACROPTERA GOVLDI

The Grey-faced Petrel is a non-migratory winter breeder whose reproductive season occupies 9–10 months. Males spend more time in the burrows than females during the courtship period. Some females keep company with strange males, and may be fertilized by them, but subsequently share incubation with their mate of the previous year. The duration of the pre-laying absence of females is about two months, and of the pre-incubation absence of males about seven weeks. Since copulation is presumed to occur before this absence, these petrels seem to have evolved prolonged viability of the spermatozoa, though ovulation may take place some time before laying. Eggs are laid in late June or July but chicks are rarely reared from eggs laid after 14 July; effective laying thus lasts three weeks. The single egg is about 15·5% of the female's weight; she may be able to exert slight control over timing of oviposition. She may be required to incubate, if capable, for up to 14 days from laying but the male takes over, on average, after four days. There are three main incubation spells of 17 days' average duration, two by the male. These are of a duration such that there is usually a change-over near hatching. Incubation lasts about 55 days. There is competition for burrows, resulting in two-egg nests. Norway Rats take unattended eggs and young chicks and scavenge, but their predation (less than 10–35% of chicks per year) is not considered to be endangering the population. After initially more frequent feeds, chicks are fed approximately once a week by each parent. They do not become much heavier than adults and the growth rate is slow: about 120 days to departure. The ability to begin breeding in winter, atypical of petrels in this region, may be facilitated by three factors: improved availability of food resulting from longer nocturnal feeding time and reduced inter-specific competition; the ability to lay fertile eggs two months or more after copulation; and the brevity of the non-breeding season due to the relative proximity of a sufficient food supply.     

Systematics of the Soft-plumaged Petrel Pterodroma mollis (Procellariidae): new insight from the study of vocalizations

The taxonomic status of the populations of the polytypic Soft-plumaged Petrel Pterodroma mollis is controversial. Previous taxonomic studies used morphological characters (measurements and colouration) and univariate statistics. In this study, I add the use of multivariate statistics on morphological (biometry and colouration) and behavioural characters (vocalizations) of the petrels. Vocalizations are especially relevant in nocturnal burrowing petrels (such as the Soft-plumaged Petrel) and act as behavioural isolating mechanisms. The analysis, based on 535 calls from seven of the 11 known breeding localities of the species, showed that physical parameters of the call did not overlap at all between breeding localities in the northern and southern hemispheres but did so within each hemisphere. Conversely, the morphological analysis, based on morphometries from ten localities, displayed wide and significant intra-hemisphere variation, whereas there was no consistent difference between northern and southern parts of the breeding range. Thus analysis of the two sets of characters gave contradictory results. Calls, owing to their role in species-specific recognition in these birds, should be given priority over other characters for species separation. I suggest that only two species should be recognized, Pterodroma mollis and Pterodroma feae, with three subspecies each. I also examined behavioural affinities between P. mollislfeae groups and other gadfly petrels and found that P. mollis/feae were closest to Pterodroma cahow, whilst Pterodroma hasitata on the one hand and Pterodroma phaeopygia and Pterodroma externa (which may comprise two species instead of one) on the other belong to other groups of gadfly petrels.     

THE OCCURRENCE AND DISTRIBUTION OF ACRASIEAE IN FORESTS OF SUBTROPICAL AND TROPICAL AMERICA

Forests of the subtropical and tropical regions of North America harbor cellular slime molds not found in the soils of temperate deciduous forests investigated previously. However, most species found in the temperate forest are common in the tropics. Although the diversity of forms is greater in the soils of tropical forests the numbers of Acrasieae per unit of soil are comparable. Characteristic of tropical and subtropical forest soils are Acrasieae bearing crampon bases, of which four new species of Dictyostelium are presently known. Also present, but less frequently isolated, are two other new species of the genus Dictyostelium and two still undescribed species of the Guttulinaceae. Occasional isolates of D. purpureum and D. discoideum were found that produce macrocysts, which seem, also, to be confined to tropical and subtropical areas. Macro-cysts were previously known only in D. mucoroides and D. minutum isolated from temperate forest soils. The occurrence and distribution of Acrasieae in warm temperate desert and mesquite-scrub, in subtropical hammock, and in tropical thorn, deciduous, seasonal evergreen, rain, and cloud forests were investigated. Acrasieae were well represented in all of these forests except desert. The number of species and the total populations were largest in seasonal evergreen forests. The composition of the cellular slime mold populations and the dominant species within these populations could be related to the soil environment as expressed by the dominant vegetation.     

Range expansion and hybridization in Round Island petrels (Pterodroma spp.): evidence from microsatellite genotypes

Historical records suggest that the petrels of Round Island (near Mauritius, Indian Ocean) represent a recent, long‐distance colonization by species originating from the Atlantic and Pacific Oceans. The majority of petrels on Round Island appear most similar to Pterodroma arminjoniana, a species whose only other breeding locality is Trindade Island in the South Atlantic. Using nine microsatellite loci, patterns of genetic differentiation in petrels from Round and Trindade Islands were analysed. The two populations exhibit low but significant levels of differentiation in allele frequencies and estimates of migration rate between islands using genetic data are also low, supporting the hypothesis that these populations have recently separated but are now isolated from one another. A second population of petrels, most similar in appearance to the Pacific species P. neglecta, is also present on Round Island and observations suggest that the two petrel species are hybridizing. Vocalizations recorded on the island also suggest that hybrid birds may be present within the population. Data from microsatellite genotypes support this hypothesis and indicate that there may have been many generations of hybridization and back‐crossing between P. arminjoniana and P. neglecta on Round Island. Our results provide an insight into the processes of dispersal and the consequences of secondary contact in Procellariiformes.     

Diving behaviour of white-chinned petrels and its relevance for mitigating longline bycatch

The white-chinned petrel (Procellaria aequinoctialis) is the seabird species most commonly killed by Southern Hemisphere longline fisheries. Despite the importance of diving ability for mitigating longline bycatch, little is known of this species’ diving behaviour. We obtained data from temperature–depth recorders from nine white-chinned petrels breeding on Marion Island, southwestern Indian Ocean, during the late incubation and chick-rearing period. Maximum dive depth (16 m) was slightly deeper than the previous estimate (13 m), but varied considerably among individuals (range 2–16 m). Males dived deeper than females, and birds feeding chicks dived deeper than incubating birds, but dive rate did not differ between the sexes. Time of day had no significant effect on dive depth or rate. Our findings will help to improve the design and performance of mitigation measures aimed at reducing seabird bycatch in longline fisheries, such as the calculation of minimum line sink rates and optimum aerial coverage of bird-scaring lines.