Halobaena Research Articles

One House Two Families: Petrel Squatters Get a Sniff of Low‐Cost Breeding Opportunities

SummaryBurrowing is a widespread nesting behaviour, found in vertebrates and invertebrates. It is particularly common in small procellariiform seabirds such as blue petrels (Halobaena caerulea) and Antarctic prions (Pachyptila desolata), two closely related petrel species. However, digging a burrow is costly and alternative strategies may evolve. Accordingly, blue petrel males can adopt two alternative nesting strategies: digging a new burrow or squatting in an empty one. Importantly, a blue petrel squatter arriving at the colony to breed is more likely to find empty Antarctic prion burrows than empty blue petrel burrows, since the former species only start breeding a month later. However, squatting in a prion’s burrow is risky for blue petrels as the legitimate owner very often returns and claims the burrow back, thus ruining the squatter’s breeding attempt. We present here results of a survey of two sympatric colonies of blue petrels and Antarctic prions on Kerguelen Island. Our data show that blue petrel squatters preferentially occupy blue petrel empty burrows. To investigate potential underlying mechanisms behind this preference, we used a simple Y‐maze design to show that blue petrels can discriminate and prefer their specific odour over the prion odour. Our results confirm the existence of alternative burrowing strategies in blue petrels and suggest that squatters could use olfaction to avoid the less suitable Antarctic prion burrows.

Patterns of variation of serum oxidative stress markers in two seabird species

Variation in oxidative stress markers in natural populations may provide a useful background for understanding variation in life history strategies. In this study, we seek to evaluate patterns of variation in levels of reactive oxygen metabolites (markers of oxidative damage), serum antioxidant capacity, and serum concentration of thiols (antioxidants endogenously synthesized) in nestling and breeding blue petrels (Halobaena caerulea) and in breeding Antarctic prions (Pachyptila desolata). Male and female prions and nestling petrels did not differ in any of the oxidative stress markers. The serum antioxidant capacity positively correlated with the sample time in nestling blue petrels. Breeding petrels with higher body condition index had higher serum antioxidant capacity and circulating thiols. Finally, both seabird species showed lower levels of reactive oxygen metabolites and higher levels of serum antioxidant capacity than previously studied bird species.

Olfaction in Petrels

In the 1960s, Betsy Bang unraveled the complexity of the olfactory apparatus of procellariiform seabirds (petrels and albatrosses), suggesting an important role for olfaction in their ecology. Shortly thereafter, Prof. B. Wenzel continued the investigations on petrels' well-developed olfactory neuroanatomy as well as their sensitivity to food-related scents. Later studies demonstrated further that the sense of smell is also critical to these birds when homing to their burrow. Building on these findings, we have demonstrated in several petrel species the importance of the burrow olfactory signature in homing. The nature of this olfactory signature relies predominantly on their mate's odor. Indeed, in our Y-maze experiments, Antarctic prions (Pachyptila desolata) and blue petrels (Halobaena caerulea) could discriminate between their own and their mates' odors. However, although they are attracted by their mate odor, they prefer the odor of a conspecific bird to their own. These results have drawn attention to the possible use of chemical signals in birds' social behaviors, such as individual recognition and/or mate choice. Indeed, petrel life history traits suggest that olfactory-mediated mate choice may have evolved in this group to ensure genetic compatibility between mates. We have recently shown that a bird's semiochemical profile is more similar to itself, year after year, than to that of a conspecific. As a result, a novel function of olfaction emerges in petrels: the perception of a chemical signal that may broadcast individuals' identity and quality, thereby contributing to an optimal mate choice.

Atypical homing or self-odour avoidance? Blue petrels (Halobaena caerulea) are attracted to their mate’s odour but avoid their own

Among procellariiform seabirds, many burrowing petrels show good olfactory abilities especially in recognising their nest. In particular, it has been reported that Antarctic prions (Pachyptila desolata) discriminate their own and their mate’s odours and, in Y-maze experiments, prefer the odour of a conspecific bird to their own. While traditionally examined from the perspective of homing mechanisms, these recent results have drawn attention to the possible use of chemical signals in birds’ social behaviours. Indeed, the life history of petrels suggests that a mate choice mediated by olfactory mechanisms may have evolved in this group to ensure genetic compatibility. This study was undertaken to validate and extend results obtained on petrels’ olfactory discrimination capabilities. Following the Y-maze experiment protocol, blue petrels (Halobaena caerulea) were offered three different choices: (1) mate versus conspecific’s odour, (2) own versus mate’s odour and (3) own versus conspecific’s odour. We discovered that birds prefer the odour of their mate not only when presented against conspecific’s odour but also against their own. We further verified that blue petrels also avoid their own odour when presented against conspecific’s odour. Our results confirm that olfactory discrimination in burrowing petrels goes beyond self-recognition and that self-odour avoidance may be widespread. We use two mutually non-exclusive behavioural frameworks for the interpretation of our results, homing and mate choice, and explain why homing mechanisms cannot account for all of our observations. This study opens the door to further research on olfactory mechanisms that, in petrels, might mediate individual recognition and mate choice.

Interannual dietary changes and demographic consequences in breeding blue petrels from Kerguelen Islands

Interannual variation in summer diet and demographic parameters of blue petrel Halobaena caerulea were investigated to understand how changes in the marine environment affect the reproduction of an oceanic seabird from the Southern Ocean. Lipids from stomach oil were used as trophic markers of prey consumed by adult birds when they self-fed during long trips, and conven- tional food analyses allowed determination of the food delivered to chicks after long and short adult foraging trips. Biochemical analysis of stomach oil showed little differences in lipid classes and in fatty acid and fatty alcohol compositions, with most oils deriving from triacylglycerol- and wax ester- rich myctophid fishes over the 4 yr study period (1996, 2000, 2001 and 2002). Accordingly, stomach content analysis showed that chick food was dominated by mass by crustaceans and fish, with myc- tophids as the main fish items. Important interannual variations in chick diet occurred, most promi- nently featuring an almost lack of fish in 2002. Summer 2002 was also marked by the lowest fledging success, lowest mass of chicks at fledging and lowest summer survival of adults during the period 1986-2002. In contrast to 1996, 2000 and 2001, summer months in 2002 were also characterized by an intense warm event in Kerguelen waters. Overall, results strongly suggest causal links between cli- matic anomalies, availability of myctophids and dietary shifts with poor reproductive performance and lower survival in blue petrel. Furthermore, they emphasize the importance of lipid-rich prey in seabird nutrition.

The response of burrow-nesting petrels and other vulnerable bird species to vertebrate pest management and climate change on sub-Antarctic Macquarie Island

Pest species management is causing rapid and significant changes to burrow-nesting petrel populations on sub-Antarctic Macquarie Island. The Weka, Gallirallus australis, was eliminated by 1989 and the Feral Cat, Felis catus, eradicated in 2000. The most abundant burrownesting petrel species currently, White-headed Petrels, Pterodroma lessonii, Antarctic Prions, Pachyptila desolata, and Sooty Shearwaters, Puffinus griseus, have yet to increase in numbers, but are expected to do so in the absence of cats. This study found evidence that Grey Petrels, Procell aria cinerea, began breeding again on the island in 1999, after an absence of over 100 years. Blue Petrels, Halobaena caerulea, and Fairy Prions, Pachyptila turtur, were found to be re-colonising Macquarie Island from offshore stacks after a similar absence. South Georgian Diving-Petrels, Pelecanoides georgicus, were also possibly recolonising the island. Despite the presence of Black Rats, Rattus rattus, most of the bird species discussed are considered capable of population increase. If European Rabbits, Oryctolagus cuniculus, are not eliminated or maintained in reduced numbers, some petrel populations will never fully recover. Climate change could have a negative impact on burrow-nesting petrels, and is likely to exacerbate the detrimental effects of the remaining pest species on vulnerable indigenous bird species, compounding the need for remedial action against rabbits in particular. Together with predictions that other petrel species will now return to breed, certain terrestrial bird species, alien to the region, may invade Macquarie Island as a consequence of the combination of pest eradication and changing climatic conditions.

Lipids from stomach oil of procellariiform seabirds document the importance of myctophid fish in the Southern Ocean

We investigated the relative importance of myctophid fish and Antarctic krill in the diet of adult flying seabirds of the Southern Ocean. The main prey of short‐tailed shearwaters Puffinus tenuirostris (P. ten.), white‐chinned petrels Procellaria aequinoctialis (P. aeq.), blue petrels Halobaena caerulea (H. cae.), thin‐billed prions Pachyptila belcheri (P. bel.), and Antarctic prions Pachyptila desolata (P. des.) were mostly deduced from the lipid analysis of adult stomach oils. More than 97% of the 125 analyzed oils mainly consisted of wax esters (WEs) and triacylglycerols (TAGs) (>70% of total lipids). WE fatty alcohol (FAlc), WE fatty acid (FA), and TAG‐FA profiles clearly segregated P. aeq. from P. ten., with smaller, but still significant, differences among the three other petrel species. P. aeq. and P. ten. therefore preyed on distinct prey species, whereas H. cae., P. bel., and P. des. had a more similar diet, but still with some prey differences. Comparisons between FAlc and FA patterns of oils with those of potential prey species showed that >93% of FAlc and FA patterns of oil WEs had a high probability of resemblance with the myctophid signatures, and similar results were obtained with the TAG fractions. Almost no stomach oil fit the lipid patterns of subantarctic and Antarctic euphausiids, including those of the WE‐rich Thysanoessa macrura and the TAG‐rich Antarctic krill Euphausia superba. This study thus demonstrates for the first time the importance of myctophids in the nutrition of adult flying seabirds breeding in subantarctic islands and foraging in Antarctic waters during the austral summer.

Behavioural responses of blue petrel chicks (Halobaena caerulea) to food-related and novel odours in a simple wind tunnel

As a first step towards understanding the development of olfactory behaviours in Antarctic procellariiform seabirds, we recently showed that blue petrel chicks (Halobaena caerulea) could detect both a food-related and a novel odour while asleep. In this current study, we tested chicks in a simple wind tunnel to determine if exploratory behaviours could be initiated by olfactory stimuli as well. We compared the behavioural responses of 30 blue petrel chicks to cod liver oil (a prey-related odour) or phenyl ethyl alcohol (an unfamiliar, rosy-smelling odourant) against a control (distilled water). Six behavioural indices were measured, including head turns, body turns, bites, preening events, wing-stretches, and distance walked. In response to cod liver oil, we found that chicks increased both turning rates and distances walked whereas chicks preened more in response to phenyl ethyl alcohol. Since only cod liver oil initiated behaviours consistent with searching, our results suggest that chicks are attaching biological significance to food-related odours even before they leave the burrow to forage for the first time.

The potential role of ammonia as a signal molecule for procellariiform seabirds

Procellariiform seabirds (petrels, albatrosses and shearwaters) navigate vast distances over seemingly featureless ocean habitat by mechanisms that are not well understood. These birds have large olfactory bulbs, and the use of smell has been implicated in both foraging and homing behavior. While many olfactory cues relevant to these behaviors have been identified, ammonia is a potentially significant, biogenic, scented compound that has not been studied in this context. Ammonium (NH4+) constitutes a primary waste product produced by many of the prey species on which procellariiforms forage. Nitrogen waste products, including volatilized ammonia (NH3) also scent the terrestrial landscape of sub-Antarctic islands where newly breeding procellariiform seabirds recruit and raise their young. Since an ability to smell ammonia may be relevant to both prey detection and locating colonies or islands, we used a non-invasive, behavioral assay to examine whether this scented compound is detectable by a candidate test species, the blue petrel Halobaena caerulea Gmelin. Our results suggest that these birds can detect volatilized ammonia within a concentration range that they may naturally encounter (10(-11) to 10(-5) M), and point to ammonia as a potential signal molecule in the sub-Antarctic.

Evidence that blue petrel,Halobaena caerulea,fledglings can detect and orient to dimethyl sulfide

Procellariiform seabirds (the petrels, albatrosses and shearwaters) are recognized for their acute sense of smell. These pelagic seabirds forage over thousands of miles of ocean to find patchily distributed prey resources. Over the past decade, much headway has been made in unravelling the variety of olfactory foraging strategies that Antarctic species employ, and it is becoming clearer that olfaction plays a key role in foraging, particularly for burrow nesting species. Now we are beginning to explore how these behaviours develop in chicks. Procellariiform chicks fledge and survive the open seas without aid or instruction from a parent, but how they are able to accomplish this task is unknown. Here we explore whether chicks leave the nest pre-tuned to olfactory cues necessary for foraging. In this study, we tested the hypothesis that blue petrel chicks (Halobaena caerulea) are able to detect and orient to a foraging cue (dimethyl sulphide, DMS) used by adults without ever having experienced this odour at sea. We first established that chicks could detect DMS at a biologically relevant concentration that they will later naturally encounter at sea (<10 pmol l-1). We then performed preference tests in a Y-maze on a group of birds 1-6 days before they fledged. Sixteen out of 20 fledglings preferred DMS (e.g. DMS+propylene glycol) to a ;control' odour (propylene glycol alone). Our results suggest that chicks can detect and may already recognize DMS as an orientation cue even before they leave the nest to forage for the first time.

Population census of blue petrels Halobaena caerulea at Mayes Island, Iles Kerguelen

The blue petrel (Halobaena caerulea) is a small pelagic seabird breeding on just a few Southern Ocean islands. Although it is known that oceanographic and climatic variability affect mortality rates, individual body condition and reproductive success, very few data are available on the global population status. We assessed the status of blue petrels at Mayes Island, Iles Kerguelen, in 2002 by estimating burrow densities and burrow occupancy using acoustic playbacks and response probability. The mean and highest burrow densities recorded were respectively 0.136 ± 0.026 and 2.3 entrances per m2. Burrow occupancy increased with burrow density but stabilized at c. 0.6 occupied burrows per m2. Taking into account the response probability to playback (0.819) the mean burrow occupancy density was 0.037 ± 0.094 per m2, giving an estimated 142 000 (95% CI around 106 000–179 000) or 148 000 breeding pairs (95% CI around 55 000–241 000) on Mayes Island, respectively with and without taking into account spatial autocorrelation in burrow densities. This suggests that the entire breeding population of blue petrels at Kerguelen is much higher than current estimates, and that Kerguelen and Diego Ramírez archipelagos are key breeding sites for this species.

Stable isotope evidence of diverse species-specific and individual wintering strategies in seabirds

Although there is increasing evidence that climatic variations during the non-breeding season shape population dynamics of seabirds, most aspects of their winter distribution and ecology remain essentially unknown. We used stable isotope signatures in feathers to infer and compare the moulting (wintering) habitat of subantarctic petrels breeding at two distant localities (South Georgia and Kerguelen). Petrels showed species-specific wintering habitat preferences, with a similar pattern of latitudinal segregation for all but one taxon. At both localities, delta13C values indicated that blue petrels (Halobaena caerulea) moult in Antarctic waters, South Georgian diving petrels (Pelecanoides georgicus) in the vicinity of the archipelagos and/or in the Polar Frontal Zone and Antarctic prions (Pachyptila desolata) in warmer waters. In contrast, common diving petrels (Pelecanoides urinatrix) showed divergent strategies, with low and high intrapopulation variation at South Georgia and Kerguelen, respectively. Birds from Kerguelen dispersed over a much wider range of habitats, from coastal to oceanic waters and from Antarctica to the subtropics, whereas those from South Georgia wintered mainly in waters around the archipelago. This study is the first to show such striking between-population heterogeneity in individual wintering strategies, which could have important implications for likely demographic responses to environmental perturbation.

An estimate of population sizes of burrowing seabirds at the Diego Ramirez archipelago, Chile, using distance sampling and burrow-scoping

The Diego Ramirez Islands lie 60 nautical miles southwest of Cape Horn and are the breeding site for three species of burrowing seabirds: blue petrels (Halobaena caerulea), common diving petrels (Pelecanoides urinatrix) and sooty shearwater (Puffinus griseus). Burrowing seabirds are highly vulnerable to predation by introduced vertebrate pests, and Diego Ramirez is an important breeding site because it is one of a few remaining subantarctic island groups with no introduced predators. Diego Ramirez is the only known breeding site for blue petrels in the southeast Pacific region, holding about 80% of the global population of that species, and with a population ten times larger than any other population in the world. We estimated the population size in 2002, using a novel application of the distance sampling technique to determine burrow density, and a burrow-scope with excavations to determine occupying species. We found that density was correlated with slope angle and soil wetness. Burrow densities in flatter terrain with drier soils were 2.03 burrows/m2 (95% confidence intervals: 1.82–2.27) and 1.11 burrows/m2 (0.84–1.48) in steeper terrain with wetter soils. The occupation rate of burrows were significantly different between habitat types (t=2.74, d.f. 11, P<0.05); in flatter drier habitats the proportion of burrows that led to a nest was 0.85 (0.74–0.96), in steeper wetter habitats this decreased to 0.64 (0.50–0.78). We used a digital elevation model to calculate true area rather than planar area for the two habitat types on the main island of Bartolome, and charts to calculate planar area for the remainder of the archipelago. There were 1.35 (1.15–1.54) million pairs of blue petrels and 99,000 (65,000–134,000) pairs of common diving petrels on the archipelago. These are similar figures to those from the only previous estimate, made in 1980. We found breeding sooty shearwaters for the first time, and estimated a population of several thousand pairs. We emphasise the facility of distance sampling as an unbiased technique with practical advantages over commonly used area search methods for monitoring populations of burrowing seabirds. These advantages include increased survey efficiency allowing a larger sample size for a given effort and a correspondingly tighter estimation of density.

ENVIRONMENTAL CONDITIONS AND BREEDING EXPERIENCE AFFECT COSTS OF REPRODUCTION IN BLUE PETRELS

Using data from a 17-year study of individually marked Blue Petrels, we examined how survival and breeding probability varied with experience and breeding status, and looked for costs of first reproduction, taking into account environmental and individual variability. Using multistate capture–recapture models with four states (inexperienced nonbreeders, first-time breeders, experienced breeders, and experienced nonbreeders), we found that first-time breeders had a lower probability of surviving and breeding in the next year than experienced breeders. Survival of first-time breeders was lower than that of inexperienced nonbreeders, indicating a cost of first reproduction. Survival of inexperienced individuals (both breeders and nonbreeders), but not of experienced ones, was negatively affected by poor environmental oceanographic conditions. The costs of reproduction for first-time breeders were particularly marked during harsh weather conditions. Survival and the probability of breeding in the next year for experienced birds were higher for breeders than for nonbreeders. Similarly, the probability of breeding in the next year for first-time breeders was higher than for inexperienced nonbreeders. This suggests heterogeneity in quality among individuals. Experienced breeders had a higher body condition than first-time breeders and nonbreeders. Body condition did not affect the probability of surviving or breeding in the next year. These results can be interpreted in the light of a change in the proportion of individuals with different survival (selection hypothesis: low-quality individuals die sooner). The inferiority of first-time breeders may be linked to a higher proportion of lower-quality individuals in younger age classes. First reproduction may act as a filter, selecting individuals of higher quality. Sea surface height, reflecting food availability, is probably a key selective agent.

The distribution of seabirds and pinnipeds in Marguerite Bay and their relationship to physical features during austral winter 2001

Abstract The distribution of seabirds and pinnipeds and their relationship to physical oceanographic variables were investigated as part of the US Southern Ocean Global Ocean Ecosystem Dynamics field program along a study grid centered around Marguerite Bay on the west Antarctic Peninsula during late fall (April–May) and winter (July–August), 2001. Sea-ice conditions during the cruises provided an opportunity to compare the relationship among physical oceanographic variables and species distributions before and after the development of pack ice. During the fall cruise before pack ice development, both sea-ice-affiliated species and open-water-affiliated were observed in the area. The most common ice-affiliated species observed at this time were snow petrel ( Pagodroma nivea , 0.7 individuals km −2 ) and Antarctic petrel ( Thalassoica antarctica , 0.2 individuals km −2 ) and the most common open-water-affiliated species were blue petrel ( Halobaena caerulea , 0.4 individuals km −2 ), cape petrel ( Daption capense , 0.2 individuals km −2 ), and southern fulmar ( Fulmarus glacialoides , 0.1 individuals km −2 ). In addition, Antarctic fur seals ( Arctocephalus gazella , 0.1 individuals km −2 ) and crabeater seals ( Lobodon carcinophagus , 0.4 individuals km −2 ) were observed in low numbers. Akaike's information criterion was used to assess competing models that predicted predator distributions based on physical oceanographic variables proposed to structure predator distribution in previous research. These analyses indicated that predator distributions were primarily associated with water-mass structure and variability in bottom depth during the fall cruise. Crabeater seal, snow petrel, Antarctic petrel, and southern fulmar had higher densities in Inner Shelf Water, particularly near Alexander Island where a coastal current was present. Blue petrel, kelp gull ( Larus dominicanus ), and southern giant petrel ( Macronectes giganteus ) were positively associated with variability in bottom depth in April–May, suggesting that hydrographic processes influenced by bathymetry may have been important in structuring bird distributions. After the development of pack ice, during July and August, only sea-ice-affiliated species, including snow petrel (1.0 individuals km −2 ), Antarctic petrel (0.1 individuals km −2 ), Adelie penguin ( Pygoscelis adeliae , 0.4 individuals km −2 ), and crabeater seal (0.3 individuals km −2 ), were observed. Seabirds were primarily associated with sea-ice characteristics (e.g. sea-ice concentration, sea-ice type) rather than the water-column environment later in the winter. Results from this study suggest that the timing and extent of sea-ice development in the fall may influence over-winter predation by seabirds and pinnipeds on zooplankton and fish on the western Antarctic Peninsula. Delays in sea-ice development may allow seabirds and pinnipeds access to biologically important areas such as the Inner Shelf Water for a longer period of time thereby increasing predation on zooplankton and fish.

Recognition of burrow's olfactory signature in blue petrels, Halobaena caerulea: an efficient discrimination mechanism in the dark

Previous work has shown that blue petrels need olfaction to home. We investigated whether they also recognize an olfactory signature of their own nest. We performed T-maze experiments in which maze arms were connected with the subject bird's burrow and with the burrow of a conspecific neighbour. Of 23 birds, 16 were able to recognize the arm leading to their own burrow. In a second experiment, we positioned the maze in front of the subject's burrow but the maze arms were closed and did not enter the burrow. Consequently, no burrow odours could be sensed by the bird. In this case, 85% of birds (17 of 20) failed to choose, suggesting that petrels were not motivated to choose by positional cues in the absence of odour cues. We explored this idea further by performing a homing experiment whereby homing birds had to relocate an artificially displaced burrow entrance. Blue petrels homed, ignoring the natural burrow entrance and using the new artificial one. The ability to smell their own burrow allows blue petrels to return to the colony at night and to find the correct nest.

Influence of the diet on the bioaccumulation of heavy metals in zooplankton-eating petrels at Kerguelen archipelago, Southern Indian Ocean

Concentrations of cadmium, mercury, copper and zinc were measured in muscle, kidney and liver tissues and in the main prey of five species of zooplankton-eating petrels: blue petrel (Halobaena caerulea), thin-billed (Pachyptila belcheri) and Antarctic (P. desolata) prions, and South Georgian (Pelecanoides georgicus) and common (Pelecanoides urinatrix) diving petrels. Since some of these species are closely related species with respect to body size, timing ofmoult and life span, their diet has been examined to evaluate its influence on heavy-metal bioaccumulation. Inter-specific differences were significant for Hg concentrations in the liver and for Zn concentrations in both liver and kidney tissues. Blue petrels exhibited the highest Hg concentrations in the liver (3.9±2.02 lg.g)1 wet weight). No significant differences were found in Cd concentrations between species. Exposure to heavy metals through the most important prey species in the diet during the breeding period was evaluated. The most evident result was the influence of fish prey on Hg levels. Although crustacean species exhibit different cadmium concentrations, the diet composition does not appear to be discriminant for Cd bioaccumulation within the small petrel community at Kerguelen.

Climate and density shape population dynamics of a marine top predator

Long-term studies have documented that climate fluctuations affect the dynamics of populations, but the relative influence of stochastic and density-dependent processes is still poorly understood and debated. Most studies have been conducted on terrestrial systems, and lacking are studies on marine systems explicitly integrating the fact that most populations live in seasonal environments and respond to regular or systematic environmental changes. We separated winter from summer mortality in a seabird population, the blue petrel Halobaena caerulea, in the southern Indian Ocean where the El Niño/Southern Oscillation effects occur with a 3-4-year lag. Seventy per cent of the mortality occurred in winter and was linked to climatic factors, being lower during anomalous warm events. The strength of density dependence was affected by climate, with population crashes occurring when poor conditions occurred at high densities. We found that an exceptionally long-lasting warming caused a ca. 40% decline of the population, suggesting that chronic climate change will strongly affect this top predator. These findings demonstrate that populations in marine systems are particularly susceptible to climate variation through complex interactions between seasonal mortality and density-dependent effects.

CHICKS SNOOZE TO SNIFF

By the time a 45-day-old blue petrel chick emerges from its burrow to embark on its maiden foraging flight, both parents have taken off, leaving the youngster to fend for itself. So how does the youngster know what to look for when hunting krill? Gabrielle Nevitt is fascinated by the way procellariiform seabirds, such as blue petrels and thin billed prions, track down food with their sense of smell, and wondered whether the youngsters recognise their prey's smell even before they have left their burrow. Working with Henri Weimerskirch and Francesco Bonadonna in France, Nevitt and her lab decided to test the chick's responses to a range of smells, some of which they'd encounter in their natural surroundings(p. 1615).However, Nevitt suddenly had to cry off on the eve of departing for the sub-Antarctic, so Greg Cunningham stepped into the breach and headed south to join Weimerskirch's team, where they intended to record the chick's reactions using a noninvasive electrophysiological test. And when they finally arrived at the shack that would be their laboratory for the next month, the electricity supply was too unreliable to use for the sensitive tests; `it was a frustrating time' remembers Nevitt. But Cunningham had a backup plan. Just before leaving California, he had read a paper describing how sleeping chicken chicks responded to puffs of odours by `peeping' gently in their sleep. Could he get the same response from dozing petrel chicks?He headed back out to the nesting site to retrieve chicks from their burrows, before lulling them to sleep with the warmth from a light bulb and testing out their nostrils with dimethyl sulphide (DMS). The simple approach worked spectacularly well! The blue petrels and prions stirred, and sometimes even woke up, whenever Cunningham puffed a whiff of DMS past their nostrils,while the diving petrel's slumber remained undisturbed.Nevitt admits she was surprised by the diving petrel's lack of response to DMS, but it could be related to their hunting strategy. There is evidence that both blue petrels and prions hunt by tracking the plumes of dimethyl sulphide that mark the site of a krill swarm, while diving petrels `fly like bumble bees over the ocean, attacking waves and... diving a considerable distance'and probably rely less on their sense of smell while tracking prey. In fact,Nevitt believes that the diving petrel chicks probably can smell DMS, but`they don't respond to it in this context' she explains.Nevitt is delighted that such a low-tech approach has proved so successful,allowing the team to reliably test large numbers of chicks in Antarctica's inhospitable conditions in the most peaceful way imaginable.

Foraging efficiency and adjustment of energy expenditure in a pelagic seabird provisioning its chick

Summary Foraging determines the intake of resources that are expended on fitness related activities, and allocation links foraging and life‐history traits, but the extent to which individuals are able to adjust energy expenditure according to allocation decisions is still poorly studied. To examine this, we studied for the first time the efficiency of foraging trips (defined as the ratio of energy gained over energy spent while foraging) in a pelagic seabird provisioning its chick by measuring simultaneously the energy flow to the chick, changes in adult body mass and foraging cost using doubly labelled water. The study was performed over two seasons. Blue petrels (Halobaena caerulea) alternate between short foraging trips (average 1·9 days, range 1–4 days) where they maximize food delivery to the chick but loose mass, and long foraging trips (7·3 days, 5–10 days) where they increase in mass. They expend 1·5–2·2 times more energy per unit of time during short trips (2561 kJ day−1 kg−1, i.e. 3·2 times the resting metabolic rate) compared to long trips (1142–1676 kJ day−1 kg−1, i.e. 1·4–2·1 the resting metabolic rate). The currency during long trips is therefore to maximize efficiency, whereas during short trips the currency is to maximize rate of energy delivery to the chick. Maximum efficiency peaks for 6‐day trips, i.e. when adult mass gain is highest, foraging costs are lowest and efficiency was extremely low during short trips. A duration of 6 days is therefore the optimal duration of long foraging trips but trips of 7 days were more common. Our study shows that self‐feeding during long trips is crucial for the success of short trips because most of the energy used during short trips is probably derived from the energy stored during long trips. Self‐feeding during short trips is probably negligible. The study indicates that surprisingly long distance foraging may not always result in higher foraging costs compared to shorter movements. It highlights the predominant role of body store usage as a mechanism for this animal to adjust energy expenditure and energetic efficiency during foraging for allocation purposes.