Heterospecific mating preferences for a feather ornament in least auklets

Auklets (Alddae, Aethiini) include five species of small, sociallymonogamous, sexually monomorphic seabirds that display a varietyof feather and bare-part ornaments during the breeding season.Previous experimental work on two auklet species has demonstratedthat some ornaments are likely to be favored by sexual selectionbecause mutual male and female mating preferences benefit individualswith the most elaborate expression of these traits. In thisstudy we experimentally investigated whether naturally crestlessleast auklets Aethia pusilla have a maring preference for foreheadcrests similar to the most prominent ornament of two other species,crested A. cristatella and whiskered auklets A. pygmaea. Ourobjective was to investigate the function of this ornament asa species-recognition mechanism or as a product of one or moreof three proposed sexual selection models that address the originof elaborate traits and preferences. During the experiment,least auklets reacted to realistic models equipped with artificialforehead crests with approximately an order of magnitude morefrequent sexual displays and greater interest, consistent withthe idea that they have a mating preference for crests, eventhough they do not naturally express this ornament This heterospecificpreference also favored large crest size. These results refutethe possibility that least auklet forehead ornamentation alonedetermines species recognition at present Among models of sexualselection considered, the results are consistent with the sensoryexploitation model, although this could not be established unequivocallybecause a viability indicator or Fisherian mechanism could havebeen involved if least auklets had an ancestor with a foreheadcrest.     

Is the citrus-like plumage odorant of crested auklets (Aethia cristatella) a defense against lice?

Plumage odors may function as chemical defenses against ectoparasites in birds. We tested this hypothesis for crested auklets (Aethia cristatella), a species of colonial seabird that emits a very strong citrus-like odor from its plumage. This odorant contains known chemical repellents. We evaluated evidence for chemical defense in this species using two approaches. First, we exposed pigeon lice to the volatiles emitted by freshly plucked plumage and by whole specimens. Louse survivorship was compared between these treatments and two controls. Second, we compared louse abundance on crested auklets versus a closely related congener that nests in close association. Louse survivorship did not differ between crested auklet treatments and controls. Comparison of ectoparasite loads showed that crested auklets had significantly higher louse abundance than least auklets (A. pusilla), even after controlling for body size. Our results failed to support two expectations for chemical defense. Presence of the crested auklet plumage odorant in our experiments did not reduce louse life span. Presence of the aldehyde odorant in nature did not reduce louse abundance on crested auklets. Hence we conclude that the aldehyde odorant is not immediately lethal to lice at natural concentrations in plumage.     

Variations in the diet of introduced Norway rats (Rattus norvegicus) inferred using stable isotope analysis

The presence of introduced Norway rats Rattus norvegicus has raised concerns for the fate of the large least auklet Aethia pusilla colony situated at Sirius Point, Kiska Island, Alaska. Previous studies have documented extreme interannual variation in least auklet reproductive success and potential drastic population declines, both of which have been attributed to the varying abundance of, and predation by, Norway rats. A diet study would resolve the uncertainty that remains about the role of rats in the auklet's reproductive failure and the colony's decline. Our main objectives here were to quantify the variation in diet of introduced Norway rats and assess predation on least auklets. Using stable isotope analysis we document wide variability in rat diet dependent on location and provide direct evidence that Norway rats are preferentially preying on least auklets at Sirius Point. In conclusion, we hypothesize that the observed wide variability in rat diet will contribute to the persistence of rats on Kiska long after auklets have been extirpated. The persistence of rats enabled by their foraging plasticity will increase their effects by creating ecological traps within which prospecting individuals will fall and be depredated. This has large conservation consequences as it suggests that when seabirds are extirpated recolonization by prospecting birds is virtually impossible and island ecosystems will continue to be negatively affected and altered as long as introduced predators, such as rats, remain within them.     

Covariation among demographic and climate parameters in whiskered auklets Aethia pygmaea

Annual survival rate and other demographic parameters of whiskered auklets Aethia pygmaea , a small planktivorous seabird, were measured at Buldir Island Alaska during 1992–2003 to provide comparative information for auk life history studies and to test for links among climate, age, productivity and survival. Using two 9  m mistnets, we captured and recaptured 384 adult and 193 sub-adult (one year old, a known-age component of our sample) birds as they arrived at the colony after dark during May and June (1,730  capture events). The best fitting model indicated a lower initial survival rate over the first year following marking (0.708±0.036 SE), and subsequent survival (mean 0.835±0.029) covarying with the Aleutian Low Pressure climate Index, with higher auklet survival in years with weak low pressure over the Aleutian Islands. Annual survival rate varied from 0.726±0.127 in 1998–99 to 0.994±0.077 in 1994–95, rates similar to those previously reported for least A. pusilla and crested auklets A. cristatella . A model based only on recaptures of known-age birds indicated a lower local survival estimate over the first year following marking (age one to two years), with no other age-effects on survival. Breeding propensity by age inferred from recaptures of birds with fully-developed brood patches that were originally marked as sub-adults (one year olds) indicated 53% breeding at age two, 94% breeding at age 3, 97% breeding at age 4 and 100% breeding thereafter. The sex ratio of the sampled birds was significantly male biased (60/40), likely due to differences in behaviour between males and females during the incubation stage. Taken together, our data indicate that whiskered auklet survival and productivity covaried with continuous variation in large-scale climatic conditions, the mechanism being either negative effects of stormy North Pacific weather or indirect effects on food supplies.     

Natural variation in the sexually selected feather ornaments of crested auklets (Aethia cristatella) does not predict future survival

We evaluated whether sexually selected crest and auricular plumefeather ornaments of crested auklet (Aethia cristatella) adultscovaried with individual local survival over 11 years (1991–2001).Crested auklets (n = 364 total) were captured near breedingsites, marked with color rings, and local survival estimateswere based on color ring resightings at a breeding colony. Survivalestimates and relationships among local survival and crest length,auricular plume length, mass and tarsus were evaluated usingthe program MARK. The best models included four groups, definedby sex and ease of resighting, that differed in resighting rate(p) but not local survival rate (). This model structure effectivelyexplained sources of variation in local survival and resightabilityamong individuals. The best fitting model showed local survivalrate varying annually, while accounting for differences in resightabilityof marked individuals between the sexes and groups ([t], p[sex*easeof resighting]). Annual local survival varied from 0.940 ±0.029 (SE) in 1993–1994 to 0.767 ± 0.034 in 1997–1998and averaged 0.859 ± 0.019. We found no evidence thatcrested auklet local survival covaried with continuous variationin individuals' ornaments. Simulations indicated that our dataset was sufficient to detect a relationship between local survivaland a covariate that equaled or exceeded a range of 8%. Theimplications for competing sexual selection mechanisms of empiricallymeasured survival–ornament relationships are controversial,but our study emphasizes that survival estimates for such investigationsmust control for confounding factors such as resighting rateas well as have sufficient statistical power and time scaleto be biologically meaningful. Our results are most consistentwith the idea that the conspicuous variation in crested auklet'sshowy ornaments is arbitrary with respect to individual viabilityas quantified by their long-term survival.     

Scaling and jumping: gravity loses grip on small jumpers

There are several ways to quantify jumping performance, a common definition being the height gained by the body's centre of mass (CM) in the airborne phase. Under this definition, jump height is determined by take-off velocity. According to the existing literature on jumping and scaling, take-off velocity, and hence jumping performance is independent of size because the energy that differently sized geometrically scaled jumpers can generate with their muscles is proportional to their mass. In this article it is shown, based on a simple energy balance, that it is incorrect to presume that jump height does not depend on size. Contrary to common belief, size as such has does have an effect on take-off velocity, putting small jumpers at a mechanical advantage, as is shown analytically. To quantify the effect of size on take-off velocity, a generic jumper model was scaled geometrically and evaluated numerically. While a 70-kg jumper took off at 2.65 m/s and raised its CM by 0.36 m after take-off, a perfectly geometrically similar jumper of 0.7 g reached a take-off velocity of 3.46 m/s and raised its CM by 0.61 m. The reason for the better performance of small jumpers is their higher efficacy in transforming the energy generated by the actuators into energy due to vertical velocity of the CM. Considering the ecological and evolutionary relevance of different definitions of jump height, size-dependent efficacy might explain why habitual jumping is especially prominent among small animals such as insects.     

Repeatability of hematocrits and body mass of Gray Catbirds

ABSTRACT.   Hematocrits may provide information about the physiological condition of birds, but, to be a useful measure, information is needed concerning how hematocrits vary among individuals and over time. We examined the repeatability of hematocrits in a population of Gray Catbirds ( Dumetella carolinensis ) in Pennsylvania at several time scales and also examined the repeatability of body mass, another measure commonly used as an indicator of condition. Both hematocrit ( r = 0.64) and mass ( r = 0.65) were repeatable ( P < 0.01) for first captures between years and between first and second captures within a year ( r = 0.41 and r = 0.50, respectively; P < 0.01), but not repeatable ( P > 0.05) between captures in different months within a year ( r = 0.11 for both). Repeatability of both measures differed by sex and age. Females exhibited repeatability of hematocrit and body mass only between years, while male hematocrits were repeatable between years and between first and second captures within a season. Male mass was repeatable for all time periods. Hematocrits of younger birds were repeatable between captures within a season and their body mass was repeatable between months and weeks while hematocrits of older birds were not repeatable and their body mass was repeatable only between captures in a season. Our results indicate that hematocrits and body mass had similar repeatability coefficients overall, but that hematocrits of Gray Catbirds were a consistent trait of individuals only across years. Because repeatability between captures and months depended on sex and age, we conclude that the hematocrit is a useful measure of individual performance only in limited circumstances.     

A test of founder effect speciation using multiple loci in the auklets (Aethia spp.)

Whether speciation results more frequently from the genetic consequences of founder events or from gradual genetic divergence of large populations is a matter of debate. In this study, multiple analyses were applied to data from three loci (cytochrome b, alpha-enolase intron VIII, and MHC class II B) to test for founder effects associated with speciation in Aethia (Aves: Alcidae), a genus of seabirds thought to have undergone a rapid founder-induced radiation. Effective population sizes (N(e)) were derived from estimators of based on allelic diversity and the coalescent and from data on trans-species polymorphism. Results indicated that N(e) has been on the order of 10(5)-10(6) individuals throughout the evolutionary histories of least and crested auklets (A. pusilla and A. cristatella, respectively) and that N(e) of the ancestral species was at least 16,000 individuals. Computer simulations of MHC evolution indicated that a single-generation bottleneck at speciation could not have involved <85 individuals for each species. More moderate simulation scenarios indicated that population size could not have dropped below 2000 individuals at the time of species founding. Demographic history appears to have been stable for the auklets throughout the past several million years, and a founder effect associated with their speciation is unlikely.     

Experimental evidence for mutual inter- and intrasexual selection favouring a crested auklet ornament

During the breeding season, female and male crested auklets Aethia cristatella (Alcidae), display similar conspicuous crest ornaments composed of elongated forward-curving feathers on their foreheads. Based on quantifications of brief agonistic interactions at a large breeding colony, we found that crest length was strongly correlated with dominance within both sexes. Across the full range of crest length, individuals with longer crests were dominant over shorter-crested individuals in agonistic interactions involving same-sex adults. Within subadults (2-year-olds of unknown sex), there was a similar trend towards longer-crested individuals being dominant. In agonistic interactions involving individuals of different sex and age, adult males were dominant over adult females and adults were dominant over subadults, regardless of crest length. In an experiment in which we manipulated crest length using life-size realistic models, male auklets that responded were less aggressive to male models with longer crests than to models with normal or shorter crests, confirming that crest length by itself signals dominance status. In a related experiment in which we controlled intrasexual competition, both males and females responded to opposite-sex models with more frequent sexual displays when the models had long crests compared with those having short crests, suggesting that crested auklets also have mating preferences that favour long crest ornaments. Taken together, these results support the idea that the crest ornament is favoured by both intra- and intersexual selection. Copyright 1999 The Association for the Study of Animal Behaviour.     

Why not walk faster?

Bipedal walking following inverted pendulum mechanics is constrained by two requirements: sufficient kinetic energy for the vault over midstance and sufficient gravity to provide the centripetal acceleration required for the arc of the body about the stance foot. While the acceleration condition identifies a maximum walking speed at a Froude number of 1, empirical observation indicates favoured walk-run transition speeds at a Froude number around 0.5 for birds, humans and humans under manipulated gravity conditions. In this study, I demonstrate that the risk of 'take-off' is greatest at the extremes of stance. This is because before and after kinetic energy is converted to potential, velocities (and so required centripetal accelerations) are highest, while concurrently the component of gravity acting in line with the leg is least. Limitations to the range of walking velocity and stride angle are explored. At walking speeds approaching a Froude number of 1, take-off is only avoidable with very small steps. With realistic limitations on swing-leg frequency, a novel explanation for the walk-run transition at a Froude number of 0.5 is shown.     

Metabolic and developmental responses of alcid chicks to experimental variation in food intake.

I tested whether the ability of chicks to suspend growth and developmental processes in response to food shortages is greater among alcids with food resources that fluctuate over short time periods than it is among close relatives with food that is continuously available. I examined changes in chick resting metabolic rate (RMR) in response to short-term food deprivation in horned and tufted puffins (intermittent food provisioning) and crested and parakeet auklets (continuous food provisioning). RMR was based on measurements of chick oxygen consumption rates (Vo2) under thermoneutral conditions. RMR of postabsorptive chicks scaled allometrically with body mass, and regression slopes were statistically indistinguishable among species. Mass-independent RMR of the same individuals decreased significantly after 48 h of food deprivation. The decrease in the mass-independent RMR was greater in puffins (46.8% in horned and 47.4% in tufted puffins) than in auklets (29.4% in crested and 23.7% in parakeet auklets). To test whether the observed decrease in RMR was due to less energy being allocated to growth, I examined developmental responses of horned and tufted puffins to experimental variation in rates of food intake. I found retarded growth rates in body mass, skeletal elements, and feathers in chicks experiencing low rates of food intake. The retardation of growth processes extended the developmental period. My findings suggest that developmental plasticity in juvenile alcids might be related to temporal variability of prey in oceanic environments.     

Non-Jumping Take off Performance in Beetle Flight （Rhinoceros Beetle Trypoxylus dichotomus）

In recent decades, the take-off mechanisms of flying animals have received much attention in insect flight initiation. Most of previous works have focused on the jumping mechanism, which is the most common take-off mechanism found in flying animals. Here, we presented that the rhinoceros beetle, Trypoxylus dichotomus, takes offwithout jumping. In this study, we used 3-Dimensional （3D） high-speed video techniques to quantitatively analyze the wings and body kinematics during the initiation periods of flight. The details of the flapping angle, angle of attack of the wings and the roll, pitch and yaw angles of the body were investigated to understand the mechanism of take-off in T. dichotomus. The beetle took off gradually with a small velocity and small acceleration. The body kinematic analyses showed that the beetle exhibited stable take-off. To generate high lift force, the beetle modulated its hind wing to control the angle of attack; the angle of attack was large during the upstroke and small during the downstroke. The legs of beetle did not contract and strongly release like other insects. The hind wing could be con- sidered as a main source of lift for heavy beetle.     

Take-off flight performance in the butterfly Pararge aegeria relative to sex and morphology: a quantitative genetic assessment

Adult fitness components may strongly depend on variation in locomotory performance such as flight; this variation can be sex specific. Fast take-off to intercept females and competing males is an essential behavioral component of the territorial perching behavior in male speckled wood butterflies (Pararge aegeria L.). Females on the other hand avoid frequent take-offs particularly under suboptimal temperatures, typically showing fewer but longer flights than males. We estimated the heritability of take-off acceleration performance under suboptimal body temperatures by a restricted maximum-likelihood model. We calculated genetic correlations between this performance and a selection of morphological traits: size (body mass), flight muscle investment (relative thorax mass), and wing shape (forewing aspect ratio). Our results show significant additive genetic variation for mean acceleration performance and a similar but nonsignificant trend (P= 0.08) for maximal acceleration performance during take-off in males (h(2)= 0.15). In females, heritability was not significantly different from zero for either of the acceleration performance measures. Morphological traits and take-off performance were genetically linked in a sex-specific way. In males, relative thorax mass and forewing aspect ratio were positively genetically correlated with acceleration performance. In females, there was a negative genetic correlation between acceleration performance and abdomen mass, but not with residual abdomen mass (i.e., regressed on total body mass). To fully understand the evolution of sexual differences in flight performances and morphology, several other flight performances will have to be included. This multifunctional nature of flight and its consequences for the evolutionary study of flight has not yet been fully appreciated in the literature.     

A critique of avian CHD‐based molecular sexing protocols illustrated by a Z‐chromosome polymorphism detected in auklets

The sexes of non‐ratite birds can be determined routinely by PCR amplification of the CHD‐Z and CHD‐W genes. CHD‐based molecular sexing of four species of auklets revealed the presence of a polymorphism in the Z chromosome. No deviation from a 1:1 sex ratio was observed among the chicks, though the analyses were of limited power. Polymorphism in the CHD‐Z gene has not been reported previously in any bird, but if undetected it could lead to the incorrect assignment of sex. We discuss the potential difficulties caused by a polymorphism such as that identified in auklets and the merits of alternative CHD‐based sexing protocols and primers.     

Rates and consequences of relaying in Cassin's auklets Ptychoramphus aleuticus and rhinoceros auklets Cerorhinca monocerata breeding in a seasonal environment

We removed first eggs from early‐laying females to measure rates and consequences of relaying in Cassin's auklets Ptychoramphus aleuticus and rhinoceros auklets Cerorhinca monocerata at Triangle Island, British Columbia, Canada. Based on egg size and composition, the investment that Cassin's auklets made in first eggs was very close to that predicted from adult body mass, whereas rhinoceros auklets invested more. In both species, a high percentage of females relaid (90% of Cassin's and 87% of rhinoceros auklets). Breeding success declined weakly with later laying among control Cassin's auklet pairs, but pairs that we induced to relay bred more successfully than naturally late pairs, and similar to values predicted from laying dates of their first eggs. Their chicks also fledged heavier and younger than late control chicks, and similar to values in early control chicks, but followed the population‐wide seasonal decline in wing length at fledging. Nestling diets were dominated by Neocalanus copepods until late in the season, a sign that feeding conditions remained favourable until late. In contrast, rhinoceros auklet pairs induced to relay followed the population‐wide seasonal decline in breeding success, which was driven by a decline in hatching success. Pacific sandlance Ammodytes hexapterus, thought to be a preferred prey species, virtually disappeared from nestling diets in mid‐to‐late season, yet there was no seasonal decline in fledging mass. However, chicks from replacement eggs followed the declines among control chicks in both age and wing length at fledging. Despite the female having produced a replacement egg, and despite delayed breeding, there appeared to be little immediate consequence associated with relaying for Cassin's auklets, except for a tendency for their chicks to fledge with short wings. Consequences were more marked in rhinoceros auklets (greatly reduced hatching success, and having their chicks fledge with short wings), and this may have been due to the large investment made in eggs, and/or to delayed breeding. Results of this study show that attributes of Cassin's and rhinoceros auklets that lay at different times in the season can be important in driving seasonal declines in breeding performance, as found in studies on other Alcidae. They also show how decisions taken during the egg stage can have variable yet potentially important implications for fitness, even in relatively long‐lived species that lay single‐egg clutches.     

Yolk carotenoids and stable isotopes reveal links among environment, foraging behavior and seabird breeding success

Nutrients that are limited in availability, such as carotenoids, are potentially involved in trade-offs between homeostasis and reproduction. Despite their importance, factors that affect the capacity of female birds to meet their carotenoid requirements are poorly understood. We used δ¹⁵N stable isotope analysis to relate foraging behavior to yolk carotenoid deposition in two seabirds, Cassin’s auklet (Ptychoramphus aleuticus) and rhinoceros auklet (Cerorhinca monocerata), during each of five years. As expected from their narrower trophic range, Cassin’s auklets produced yolks with fewer carotenoid types than did rhinoceros auklets (one vs. three). Cassin’s auklets also fed on a lower trophic level diet richer in carotenoids, yet had lower total yolk carotenoid levels, which suggests a role for species-specific adaptations for carotenoid uptake and utilization. Within both species, lower trophic-level feeding was linked to higher yolk carotenoid levels, but through different mechanisms. In Cassin’s auklets, it was due to a population-wide response to environmental variation: in warm-water years, all females fed at a low trophic level and produced carotenoid-rich yolks. In rhinoceros auklets, it was due to individual differences similarly expressed in all years: females fed across a wide trophic range, and those that fed at a low trophic level produced carotenoid-rich yolks. Rhinoceros auklets bred more successfully in years when their yolks were rich in carotenoids, probably due to a correlated response to stronger marine primary production. Our results are novel because they link avian yolk carotenoid deposition to behavioral and environmental variations.     

Morphometric relationships of take-off speed in anuran amphibians

Locomotory speed correlates with muscle mass (determining force and stride rate), limb length (stride rate and distance), and laterally compressed body trunk (force and stride distance). To delineate generalization of the locomotory-morphometric relationships specifically in anuran amphibians, we investigated take-off speed and the three morphological variables from seven species, Rana nigromaculata, R. rugosa, and Bombina orientalis, Eleuthrodectilus fitzingeri, E. diastema, Bufo typhonius, Colostethus flotator and Physalaemus pustulosus. The fastest jumper E. fitzingeri (3.41 m s(-1)) showed 2.49-fold greater speed than the slowest B. typhonius. Take-off speed correlated well with both thigh muscle mass relative to body mass and hindlimb length relative to snout-vent length (HL/SVL), but poorly correlated with the inter-ilial width relative to SVL. The best morphological predictor was HL/SVL (speed=-3.28+3.916 HL/SVL, r=0.968, P<0.0001), suggesting that anuran take-off speed is portrayed well with high gear and acceleration distance characterized by hindlimbs.     

Take-off analysis of the Olympic ski jumping competition (HS-106 m)

The take-off phase (approximately 6 m) of the jumps of all athletes participating in the individual HS-106 m hill ski jumping competition at the Torino Olympics was filmed with two high-speed cameras. The high altitude of the Pragelato ski jumping venue (1600 m) and slight tail wind in the final jumping round were expected to affect the results of this competition. The most significant correlation with the length of the jump was found in the in-run velocity (r=0.628, p<0.001, n=50). This was a surprise in Olympic level ski jumping, and suggests that good jumpers simply had smaller friction between their skis and the in-run tracks and/or the aerodynamic quality of their in-run position was better. Angular velocity of the hip joint of the best jumpers was also correlated with jumping distance (r=0.651, p<0.05, n=10). The best jumpers in this competition exhibited very different take-off techniques, but still they jumped approximately the same distance. This certainly improves the interests in ski jumping among athletes and spectators. The comparison between the take-off techniques of the best jumpers showed that even though the more marked upper body movement creates higher air resistance, it does not necessarily result in shorter jumping distance if the exposure time to high air resistance is not too long. A comparison between the first and second round jumps of the same jumpers showed that the final results in this competition were at least partly affected by the wind conditions.     

Understanding how an arm swing enhances performance in the vertical jump

This investigation was conducted to examine the various theories that have been proposed to explain the enhancement of jumping performance when using an arm swing compared to when no arm swing is used. Twenty adult males were asked to perform a series of maximal vertical jumps while using an arm swing and again while holding their arms by their sides. Force, motion and electromyographical data were recorded during each performance. Participants jumped higher (0.086 m) in the arm swing compared to the no-arm swing condition and was due to increased height (28%) and velocity (72%) of the center of mass at take-off. The increased height at take-off was due to the elevation of the arm segments. The increased velocity of take-off stemmed from a complex series of events which allowed the arms to build up energy early in the jump and transfer it to the rest of the body during the later stages of the jump. This energy came from the shoulder and elbow joints as well as from extra work done at the hip. This energy was used to (i) increase the kinetic and potential energy of the arms at take-off, (ii) store and release energy from the muscles and tendons around the ankle, knee and hip joint, and (iii) ‘pull’ on the body through an upward force acting on the trunk at the shoulder. It was concluded that none of the prevailing theories exclusively explains the enhanced performance in the arm swing jump, but rather the enhanced performance is based on several mechanisms operating together.     

Strouhal number for flying and swimming in rhinoceros auklets Cerorhinca monocerata

Alcids propel themselves by flapping wings in air and water that have vastly different densities. We hypothesized that alcids change wing kinematics and maintain Strouhal numbers (St = fA/U, where f is wingbeat frequency, A is the wingbeat amplitude, and U is forward speed) within a certain range, to achieve efficient locomotion during both flying and swimming. We used acceleration and GPS loggers to measure the wingbeat frequency and forward speed of free‐ranging rhinoceros auklets Cerorhinca monocerata during both flying and swimming. We also measured wingbeat amplitude from video footage taken in the wild. On average, wingbeat frequency, forward speed, and wingbeat amplitude were 8.9 Hz, 15.3 m s^?1, and 0.39 m, respectively, during flying, and 2.6 Hz, 1.3 m s^?1, and 0.18 m, respectively, during swimming. The smaller wingbeat amplitude during swimming was achieved by partially folding the wings, while maintaining the dorso‐ventral wingbeat angle. Mean St was 0.23 during flying and 0.36 during swimming. The higher St value for swimming might be related to the higher thrust force required for propulsion in water. Our results suggest that rhinoceros auklets maintain St for both flying and swimming within the range (0.2–0.4) that propulsive efficiency is known to be high and St in both flying specialists and swimming specialists are known to converge.