SUMMARY In nearly every procellariiform species, the sense of smell appears to be highly adapted for foraging at sea, but the sense of smell among the diving petrels is enigmatic. These birds forage at considerable depth and are not attracted to odour cues at sea. However, several procellariiform species have recently been shown to relocate their nesting burrows by scent, suggesting that these birds use an olfactory signature to identify the home burrow. We wanted to know whether diving petrels use smell in this way. We tested the common diving petrel Pelecanoides urinatrix and the South-Georgian diving petrel Pelecanoides georgicus to determine whether diving petrels were able to recognise their burrow by scent alone. To verify the efficacy of the method, we also tested a bird that is known to use olfaction for foraging and nest recognition, the thin-billed prion Pachyptila belcheri. In two-choice T-maze trials, we found that, for all species,individuals significantly preferred the odour of their own nest material to that of a conspecific. Our findings strongly suggest that an individual-specific odour provides an olfactory signature that allows burrowing petrels to recognize their own burrow. Since this ability seems to be well developed in diving petrels, our data further implicate a novel adaptation for olfaction in these two species that have been presumed to lack a well-developed sense of smell.

SUMMARY Most studies investigating olfactory sensitivities in procellariiform seabirds have concentrated on adults, but little attention has been paid to how olfactory behaviours develop. We took a first step towards understanding the ontogeny of these behaviours by testing the olfactory abilities of the blue petrel Halobaena caerulea, the thin-billed prion Pachyptila belcheri, and the common diving petrel Pelecanoides urinatrix. We scored the responsiveness of chicks in a sleep-like state to puffs of odours presented near their nostrils. We tested reactions to dimethyl sulphide(DMS, a prey-related odourant) and phenyl ethyl alcohol (PEA, a novel odourant); distilled water was used as a control. Scores for blue petrel chicks were significantly greater for DMS and PEA than for control presentations, while scores for thin-billed prions were significantly greater only for PEA. Common diving petrels did not respond significantly to either odourant. These results are consistent with what is known of adult olfactory behaviours. A negative correlation between the mass of blue petrel chicks and their mean responsiveness to odours indicates that older or recently fed birds are less responsive to these stimuli.

SUMMARYAlthough it is well established that certain procellariiform seabirds use odour cues to find prey, it is not clear whether penguins use olfactory cues to forage. It is commonly assumed that penguins lack a sense of smell, yet they are closely related to procellariiforms and forage on similar types of prey in similar areas to many procellariiforms. Such regions are characterized by having high levels of dimethyl sulphide (DMS) a scented compound that many marine animals use to locate foraging grounds. If penguins can smell, DMS may be a biologically relevant scented compound that they may be sensitive to in nature. To test this hypothesis, we investigated whether adult African penguins (Spheniscus demersus) could detect DMS using two separate experiments. We tested wild penguins on Robben Island, South Africa, by deploying μmolar DMS solutions in the colonies, and found that birds slowed down their walking speeds. We also tested captive penguins in a Y-maze. In both cases, our data convincingly demonstrate that African penguins have a functioning sense of smell and are attracted to DMS. The implication of this work is that the detection of changes in the odour landscape (DMS) may assist penguins in identifying productive areas of the ocean for foraging. At-sea studies are needed to investigate this issue further.

Birds, particularly raptors, are believed to forage primarily using visual cues. However, raptor foraging tactics are highly diverse - from chasing mobile prey to scavenging - which may reflect adaptations of their visual systems. To investigate this, we studied the visual field configuration of 15 species of diurnal Accipitriformes that differ in such tactics, first focusing on the binocular field and blind area by using a single-traits approach, and then exploring the shape of the binocular field with a morphometric approach. While the maximum binocular field width did not differ between species with different foraging tactics, the overall shape of their binocular fields did. In particular, raptors chasing terrestrial prey (ground predators) had a more protruding binocular field and a wider blind area above the head than did raptors chasing aerial or aquatic prey and obligate scavengers. Ground predators that forage on mammals from above have a wide but short bill - which increases ingestion rate - and a large suborbital ridge to avoid sun glare. This may explain the protruding binocular field and the wide blind area above the head. By contrast, species from the two other groups have long but narrow bills used to pluck, flake or tear food and may need large visual coverage (and reduced suborbital ridges) to increase their foraging efficiency (e.g. using large visual coverage to follow the escaping prey in three dimensions or detect conspecifics). We propose that binocular field shape is associated with bill and suborbital ridge shape and, ultimately, foraging strategies.

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.