Sonographic evaluation of thyroid morphology during different reproductive events in female Indo‐Pacific bottlenose dolphins,Tursiops aduncus

Thyroid morphology and function are likely affected by the cyclic hormonal environment during different reproductive events in females. The present study was undertaken to evaluate the variation of thyroid morphology at different reproductive events (anestrus, estrus, lactation, and pregnancy) in a captive group of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) measured using sonography. Sonographic examinations of the thyroid gland and ovaries in nine sexually mature female subjects were performed weekly for 2.5 yr. A generalized linear mixed model was used to estimate the effects of the reproductive events for thyroid volume. Reproductive event was found to be a significant predictor for thyroid volume measurement and significant variation in thyroid volume was found between different reproductive events. A significantly larger thyroid volume in lactating females was observed when compared with estrous and anestrous females, possibly due to the high energy requirements and milk production during lactation. Taken together, thyroid volume variation during different reproductive events in female dolphins should be considered so as to obtain a diagnostically meaningful assessment when conducting routine examinations.     

AGE AND LENGTH AT WEANING AND DEVELOPMENT OF DIET OF PANTROPICAL SPOTTED DOLPHINS, STENELLA ATTENUATA, FROM THE EASTERN TROPICAL PACIFIC

Using stomach contents from 203 spotted dolphins ( Stenella attenuata ) killed in the yellowfin tuna fishery, we modeled the weaning process of calves. Spotted dolphins began to take solid food at approximately 6 mo of age, or 115 cm, but continued to suckle until they were nearly 2 yr old. Calves tended to feed more frequently on squid as they got older, which suggested there was a shift in diet during weaning. The average age and total body length at weaning was estimated to be 0.8 yr (approximately 9 mo) and 122 cm. The oldest suckling calf was almost 2 yr old, which suggests that some calves continued to suckle for more than a year after they could have been weaned. A better understanding of the weaning process, especially quantifying the period of time when calves are nutritionally dependent on their mothers may lead to a better evaluation of their potential vulnerability to the disturbance caused by the yellowfin tuna purse-seine fishery.     

Effect of lactation stage and concurrent pregnancy on milk composition in the bottlenose dolphin

Although many toothed whales (Cetacea: Odontoceti) lactate for 2–3 years or more, it is not known whether milk composition is affected by lactation stage in any odontocete species. We collected 64 pooled milk samples spanning 1–30 months postpartum from three captive bottlenose dolphins Tursiops truncatus . Milks were assayed for water, fat, crude protein (TN × 6.38) and sugar; gross energy was calculated. Ovulation and pregnancy were determined via monitoring of milk progesterone. Based on analysis of changes in milk composition for each individual dolphin, there were significant increases ( P <0.05) in fat (in all three dolphins) and crude protein (in two of three), and a decrease ( P <0.05) in water (in two of three) over the course of lactation, but the sugar content did not change. In all three animals, the energy content was positively correlated with month of lactation, but the percentage of energy provided by crude protein declined slightly but significantly ( P <0.05). At mid-lactation (7–12 months postpartum, n =17), milk averaged 73.0±1.0% water, 12.8±1.0% fat, 8.9±0.5% crude protein, 1.0±0.1% sugar, 1.76±0.09 kcal g⁻¹ (=7.25 kJ g⁻¹) and 30.3±1.3% protein:energy per cent. This protein:energy per cent was surprisingly high compared with other cetaceans and in relation to the growth rates of calves. Milk progesterone indicated that dolphins ovulated and conceived between 413 and 673 days postpartum, following an increase in milk energy density. The significance of these observed compositional changes to calf nutrition will depend on the amounts of milk produced at different stages of lactation, and how milk composition and yield are influenced by sampling procedure, maternal diet and maternal condition, none of which are known.     

Blubber morphology in wild bottlenose dolphins (Tursiops truncatus) from the Southeastern United States: influence of geographic location, age class, and reproductive state

This study investigated blubber morphology and correlations of histological measurements with ontogeny, geography, and reproductive state in live, wild bottlenose dolphins (Tursiops truncatus) from the southeastern United States. Surgical skin-blubber biopsies (N=74) were collected from dolphins during capture-release studies conducted in two geographic locations: Charleston, SC (N=38) and Indian River Lagoon, FL (N=36). Histological analysis of blubber revealed stratification into superficial, middle, and deep layers. Adipocytes of the middle blubber were 1.6x larger in Charleston subadults than in Indian River Lagoon subadults (4,590+/-340 compared to 2,833+/-335 microm2 per cell). Charleston subadult dolphins contained higher levels of total blubber lipids than Charleston adult animals (49.3%+/-1.9% compared to 34.2%+/-1.7%), and this difference was manifested in more adipocytes in the middle blubber layer (19.2+/-0.9 compared to 14.9+/-0.5 cells per field). However, dolphins from Indian River Lagoon did not exhibit this pattern, and the adipocyte cell counts of subadults were approximately equal to those of the adults (16.0+/-1.4 compared to 13.4+/-0.8 cells per field). The colder year-round water temperatures in Charleston compared to Indian River Lagoon may explain these differences. Adipocytes in the deep blubber layer were significantly smaller in lactating and simultaneously pregnant and lactating animals compared to pregnant dolphins (840+/-179, 627+/-333, and 2,776+/-586 microm2 per cell, respectively). Total blubber lipid content and adipocyte size in the deep blubber of mothers with calves decreased linearly with calf length. Lactating females may utilize lipids from the deep blubber during periods of increased energetic demands associated with offspring care. This study demonstrates that ontogeny, geography, and reproductive state may influence morphological parameters such as structural fiber densities and adipocyte numbers and sizes, measured in bottlenose dolphin blubber.     

MOTHER-INFANT SPATIAL RELATIONS IN CAPTIVE BOTTLENOSE DOLPHINS,TURSIOPS TRUNCATUS

The prolonged nursing period and strong, extended mother-infant bond observed among bottlenose dolphins may reflect social and physical ontogeny critical for infant survival. This study was conducted to quantify ontogentic changes in mother-infant contact time and the amount of time infants spent in specific spatial states with their mothers from birth to age 12 mo. These behaviors were studied through a systematic, longitudinal study of six mother-infant pairs of captive bottlenose dolphins from three different social groups. There was a significant decrease in the time infants spent with their mothers (logistic regression, P < 0.001), following the general mammalian pattern of increasing independence with age. When with their mothers, the probability that infants would be found in “echelon” position, flanking the mother, decreased as the calf aged (logistic regression, P <0.001), possibly due to anatomical and hydrodynamic factors. The probability that infants would be found in “infant” position, underneath the mother, increased with calf age (logistic regression, P < 0.001). Results obtained in this study are consistent with similar studies of wild bottlenose dolphin mother-infant pairs, indicating a suite of ontogenetically comparable behaviors between wild and captive bottlenose dolphins.     

THE DIETS OF MODERN AND HISTORIC BOTTLENOSE DOLPHIN POPULATIONS REFLECTED THROUGH STABLE ISOTOPES

The δ¹³C and δ¹⁵N compositions of teeth used in combination with existing data provide dietary information for different populations of western North Atlantic bottlenose dolphins (Tursiops truncatus). The dental isotopic signatures of bottlenose dolphins collected during the 1980s significantly differ for coastal and offshore ecotypes and are consistent with reports that coastal forms feed primarily on fish whereas offshore individuals consume more squid. In a second study, the isotopic compositions of teeth from bottlenose dolphins that span a 100-yr period and data from published stomach content analyses as well as field observations made during the past 100 yr provide evidence that coastal bottlenose dolphins from the 1880s, 1920s, and 1980s had similar diets.     

Macronutrient composition of longitudinal milk samples from captive aardvarks (Orycteropus afer)

Hand‐rearing and assisted‐rearing aardvarks in captivity has become commonplace and has led to success in breeding the species. However, the macronutrient content of aardvark milk past 1 month of age is unknown. A better understanding of aardvark milk composition would enhance captive management efforts. Here, we assayed milk samples from two captive individuals from 2 to 114 days postpartum (N = 21) for dry matter, fat, crude protein, total sugar, ash (total minerals), calcium (Ca), phosphorus (P), and gross energy. The body weight of one calf was measured from birth to weaning. Milk macronutrient composition was compared to that of other Afrotherian species and Xenarthra species with similar diets. Average protein, fat, and sugar concentrations of aardvark milk across lactation were 12.3%, 13.6%, and 2.5%, respectively. Ash averaged 1.9%, with Ca (0.50%) and P (0.35%) accounting for about 45% of total minerals. All measured nutrients increased over lactation except sugar, which decreased. Aardvark milk is high in energy (2.12 kcal/g) mostly derived from fat and protein and little energy from sugar. Calf growth was linear (r² = 0.995) with a mean gain of 159 g/day, achieving almost 30% of adult weight at weaning. Within Afrotheria, aardvark milk is higher in fat and protein and lower in sugar than elephant milk and more closely resembles the milk of its fellow insectivore, the elephant shrew. Aardvark milk is also similar in composition to milk of insectivorous Xenarthra species (nine‐banded armadillo and giant anteater). Aardvark milk composition is consistent with the species’ high‐protein diet, fast growth, and nursing pattern.     

Feeding aggregation and aggressive interaction between bottlenose (Tursiops truncatus) and Commerson’s dolphins (Cephalorhynchus commersonii) in Patagonia,Argentina

We report the first recorded interactions between bottlenose dolphin (Tursiops truncatus) and Commerson’s dolphins (Cephalorhynchus commersonii). The diurnal behavioral patterns of bottlenose dolphins in Bahía Engaño, Argentina, were similar to those described for other coastal populations around the world. The majority of the feeding bouts were recorded near the mouth the Chubut River. When not feeding near the river, bottlenose dolphins generally swam along the coast, and interactions with Commerson’s dolphins were recorded very close to the shore on two occasions during a 3-year period. In the first event, both species were feeding on a fish school. The second interaction was aggressive in nature, involving one juvenile and three adult bottlenose dolphins with several Commerson’s dolphins. Two of the adult bottlenose dolphins attacked the Commerson’s dolphins. We propose that the observed behavior represented defense of the juvenile bottlenose dolphin.

     

Nursing behaviors of beluga calves (Delphinapterus leucas) born in captivity

The nursing behaviors of two beluga whale calves were observed for the first 55 days postpartum. For both calves, the total time spent nursing in a given period peaked around 7–10 days postpartum and then declined over time. One calf, however, was found to have an unusual decline in nursing at day 35 postpartum. Ten days later, this calf was diagnosed as having a bacterial infection and given antibiotics. This suggests that early detection of health problems may be possible by observing calves' nursing behavior. For both calves, their general nursing patterns were similar, although one calf consistently nursed more than the other. Both calves nursed roughly every half hour, neither showed any signs of a circadian pattern, and carryover effects for both calves were found, indicating that there was a relationship in the overall nursing pattern from one interval to the next. That is, if nursing dropped off during one interval, it was typically made up in the next interval. Zoo Biol 16:247–262, 1997. © 1997 Wiley-Liss, Inc.     

ECOLOGY, BEHAVIOR AND SOCIAL ORGANIZATION OF THE BOTTLENOSE DOLPHIN: A REVIEW

The authors review the literature on bottlenose dolphin ecology, behavior and social organization, focusing on data collected on free-ranging animals. Most bottlenose dolphins studied to date have had definable home ranges, and behavioral, morphological and biochemical information indicates discrete stocks in some areas. Bottlenose dolphins appear to form relatively permanent social groups based on sex and age. Mother—calf bonds are long-lasting. Movement patterns are extremely variable from location to location but are relatively predictable at any given site. Food resources are one of the most important factors affecting movements. Bottlenose dolphin behavior is very flexible, and these dolphins are generally active day and night. Feeding peaks in the morning and afternoon have been observed at several sites. Social behavior is an important component of daily activities. Sharks are the most significant predator on bottlenose dolphins in most areas, but captive and wild studies show that dolphins and sharks frequently live in harmony as well. Human activities may be helpful, harmful or neutral to bottlenose dolphins, but interactions with humans are frequent for these coastal cetaceans.     

PHYSIOLOGICAL AND BEHAVIORAL DEVELOPMENT IN DELPHINID CALVES: IMPLICATIONS FOR CALF SEPARATION AND MORTALITY DUE TO TUNA PURSE-SEINE SETS

Tuna purse-seiners in the eastern tropical Pacific (ETP) capture yellowfin tuna by chasing and encircling herds of associated dolphins. This fishery has caused mortality in 14 dolphin species (20 stocks) and has led to significant depletions of at least three stocks. Although observed dolphin mortality is currently low, set frequency remains high and dolphin stocks are not recovering at expected rates. Mortality of nursing calves permanently separated from their mothers during fishery operations may be an important factor in the lack of population recovery, based on the recent discovery that calves do not accompany 75%–95% of lactating females killed in the purse-seine nets. We assessed age-specific potential for mother–calf separations and subsequent mortality of calves by reviewing and synthesizing published data on physiological and behavioral development in delphinids from birth through 3 yr postpartum. Results indicate that evasive behavior of mothers, coupled with the developmental state of calves, provides a plausible mechanism for set-related mother–calf separations and subsequent mortality of calves. Potential for set-related separation and subsequent mortality is highest for 0–12-mo-old dolphins and becomes progressively lower with age as immature dolphins approach adult stamina and attain independence.     

High calf mortality in bottlenose dolphins in the Bay of Islands,New Zealand–a local unit in decline

Bottlenose dolphins (Tursiops truncatus) in the Bay of Islands, New Zealand, have been studied for almost two decades. Since 2003, fewer than 150 dolphins visited the bay during each season and the local unit has declined 7.5% annually from 1997 to 2006. The causes of decline are unclear but probably include mortality and emigration. Here, we used a long‐term database to estimate reproductive parameters of female bottlenose dolphins including recruitment rates. A total of 704 surveys were conducted in which 5,577 sightings of 408 individually identified dolphins were collected; of these 53 individuals were identified as reproductive females. The calving rate increased between periods (1997–1999 = 0.13, CL = 0.07–0.21; 2003–2005 = 0.25, CL = 0.16–0.35 calves/reproductive female/year). A 0.25 calving rate suggests that on average, a female gives birth only once every four years, which is consistent with the estimated calving interval (4.3 yr, SD = 1.45) but still is lower than values reported for other populations. Conversely, apparent mortality rates to age 1+ (range: 0.34–0.52) and 2+ (range: 0.15–0.59) were higher than values reported elsewhere. The high apparent calf mortality in conjunction with a decline in local abundance, highlight the vulnerability of bottlenose dolphins in the Bay of Islands. Long‐term studies are required to understand the causes of high calf mortality and the decline in local abundance. Meanwhile, management should focus on minimizing sources of anthropogenic disturbance and enforcing compliance with current legislation.     

UNOBSERVED KILL OF NURSING DOLPHIN CALVES IN A TUNA PURSE-SEINE FISHERY

The kill of dolphins ( Stenella attenuata and S. longirostris ) in the eastern tropical Pacific tuna purse-seine fishery has been underestimated because of unobserved deaths of nursing calves due to separation from their mothers during fishing. Based on an analysis of dolphins killed from 1973 to 1990, and depending on the length at which calves are assumed to become independent, there was a deficit of calves relative to the number of lactating females killed in 24%–32% of 1,847 spotted-dolphin sets and in 13%–19% of 563 spinner-dolphin sets. We found a deficit of 0.31–0.45 spotted dolphin and 0.15–0.26 spinner dolphin calves per set. If these missing calves were added to the observed kill, it would represent an increase in the kill of 10%–15% for spotted dolphins and 6%–10% for spinner dolphins in the sets we examined. We did not attempt to estimate the actual number of unobserved calf deaths due to purse-seine fishing on dolphins, either in the sets we examined or in all dolphin sets. The actual number of unobserved calf deaths is likely to be higher than the calf deficit we found. Separation of dolphin mothers from calves could occur at any of several points in the fishing process, but most of these would be invisible to us and not produce a calf deficit. Estimation of the actual number of unobserved calf deaths would require further information on how frequently permanent mother-calf separations occur, the fraction of calves that survive after separation, the fraction of lactating females set upon that are carrying calves, and the fraction of calves killed that are actually related to lactating females killed in the same set. In any case, the observation of a calf deficit indicates that the reported dolphin kill fails to measure the full impact of purse-seine fishing on spotted and spinner dolphin populations.     

Evolution of milk oligosaccharides and lactose: a hypothesis

Mammalian milk or colostrum contains up to 10% of carbohydrate, of which free lactose usually constitutes more than 80%. Lactose is synthesized within lactating mammary glands from uridine diphosphate galactose (UDP-Gal) and glucose by a transgalactosylation catalysed by a complex of β4-galactosyltransferase and α-lactalbumin (α-LA). α-LA is believed to have evolved from C-type lysozyme. Mammalian milk or colostrum usually contains a variety of oligosaccharides in addition to free lactose. Each oligosaccharide has a lactose unit at its reducing end; this unit acts as a precursor that is essential for its biosynthesis. It is generally believed that milk oligosaccharides act as prebiotics and also as receptor analogues that act as anti-infection factors. We propose the following hypothesis. The proto-lacteal secretions of the primitive mammary glands of the common ancestor of mammals contained fat and protein including lysozyme, but no lactose or oligosaccharides because of the absence of α-LA. When α-LA first appeared as a result of its evolution from lysozyme, its content within the lactating mammary glands was low and lactose was therefore synthesized at a slow rate. Because of the presence of glycosyltransferases, almost all of the nascent lactose was utilized for the biosynthesis of oligosaccharides. The predominant saccharides in the proto-lacteal secretions or primitive milk produced by this common ancestor were therefore oligosaccharides rather than free lactose. Subsequent to this initial period, the oligosaccharides began to serve as anti-infection factors. They were then recruited as a significant energy source for the neonate, which was achieved by an increase in the synthesis of α-LA. This produced a concomitant increase in the concentration of lactose in the milk, and lactose therefore became an important energy source for most eutherians, whereas oligosaccharides continued to serve mainly as anti-microbial agents. Lactose, in addition, began to act as an osmoregulatory molecule, controlling the milk volume. Studies on the chemical structures of the milk oligosaccharides of a variety of mammalian species suggest that human milk or colostrum is unique in that oligosaccharides containing lacto-N-biose I (LNB) (Gal(β1 → 3)GlcNAc, type I) predominate over those containing N-acetyllactosamine (Gal(β1 → 4)GlcNAc, type II), whereas in other species only type II oligosaccharides are found or else they predominate over type I oligosaccharides. It can be hypothesized that this feature may have a selective advantage in that it may promote the growth of beneficial colonic bacteria, Bifidobacteria, in the human infant colon.     

AGE STRUCTURE AND GROWTH OF THE BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) FROM STRANDINGS IN THE MISSISSIPPI SOUND REGION OF THE NORTH-CENTRAL GULF OF MEXICO FROM 1986 TO 2003

Despite their high abundance and wide distribution, little is known about the historical or current growth and age structure of coastal bottlenose dolphins ( Tursiops truncatus ) in the north-central Gulf of Mexico. Between 1986 and 2003, teeth were collected from bottlenose dolphins stranded on the mainland coast of Mississippi and the adjacent barrier islands. Bottlenose dolphin strandings occurred year round, peaking in March and April. Neonate strandings also peaked during these 2 mo. Age estimates were obtained from 111 animals by reading the growth layer groups in the dentine layer of the teeth. The ages ranged from <1 yr to 30 yr of age. The two-stage Laird–Gompertz growth model was fitted to the total length and age data. On the basis of this model, the asymptotic lengths were estimated at 250 cm for females and 255 cm for males. The length at birth estimates were 98–103 cm for females and 100–107 cm for males. These lengths are similar to those of bottlenose dolphin populations from other Gulf of Mexico areas and from the North Atlantic Ocean along the southeastern United States.     

Incidental capture of bottlenose dolphins (Tursiops truncatus) in shark nets: an assessment of some possible causes

A minimum of 250 bottlenose dolphins, Tursiops truncatus , was caught in anti-shark nets off Natal, South Africa between January 1980 and December 1988. Males and females constituted 45.4% and 54.6% of the catch, respectively. Sexually mature males and females constituted 18.2% and 24% of the total catch, respectively. Of the latter, 65% were lactating and a further 10.3% were pregnant. Adolescents, three or more years old but not mature, contributed 12.4% of the catch. Calves, two growth layer groups (GLGs) or less in the dentine, constituted the greatest portion of the catch, almost 43%, and of these almost 70% were either weaned or weaning at capture. Analyses of biological, environmental and physiographic data for each capture suggest a number of reasons for the catch of bottlenose dolphins. The distribution of catches was random but catch rates were proportional to the number of nets. The stomachs of most dolphins were almost full at the time of capture, suggesting that enmeshing occurred either during or subsequent to feeding. Most captures were of single animals, but lactating females with calves constituted more than 25% of catches. The direction of the prevailing current was significantly related to captures. These data are examined in relation to existing knowledge of bottlenose dolphins in this area and suggest that capture may be a consequence of prey abundance at and around the nets, dolphin capture occurring either during or directly after feeding. Possible methods of reducing captures are proposed.     

Hematologic, biochemical, and cytologic findings from apparently healthy atlantic bottlenose dolphins (Tursiops truncatus) inhabiting the Indian River Lagoon, Florida, USA

The objective of this study was to establish reference baseline data for hematologic, biochemical, and cytologic findings in apparently healthy Atlantic bottlenose dolphins (Tursiops truncatus) inhabiting the Indian River Lagoon, Florida, USA. Sixty-two dolphins were captured, examined, and released during June 2003 and June 2004. Mean, standard deviation, and range were calculated for each parameter, and values for which published data were available, were close to or within the ranges previously reported for free-ranging bottlenose dolphins. No pathologic abnormalities were found in fecal and blowhole cytologic specimens. However, 24% (7/29) of the dolphins examined in 2003 had evidence of gastritis, which was graded as severe in 14% (4/29) of the cases. In 2004, only 4% (1/24) of dolphins sampled had evidence of mild or moderate gastritis; no severe inflammation was present. Dolphins with evidence of gastritis were 8 yr of age or older and predominantly male. Several statistically significant differences were found between males and females, between pregnant and nonpregnant animals, and between juveniles (<6 yr) and adults (> or =6 yr). However, the values remained within the established ranges for this species, and the differences were not likely to be of clinical significance.     

Variation in the Composition of Milk of Asian Elephants (Elephas maximus) Throughout Lactation

We investigated milk nutrient composition from three Asian elephant cows over the first 3 years of lactation, including two consecutive lactations in one cow. Body mass gain is presented for three calves during the first year. Milk samples (n = 74) were analyzed for dry matter (DM), fat, crude protein (CP), sugar, ash, calcium (Ca), phosphorus (P), and potassium (K); gross energy (GE) was calculated. Concentrations of most nutrients changed over lactation: DM, fat, CP, Ca, P, and GE were positively correlated to calf age; sugar was negatively correlated to calf age. GE doubled between birth (1 kcal/g) and 2 years of age (2 kcal/g). After accounting for calf age, GE, fat, Ca, and P concentrations differed among the cows. Milk composition also differed between two lactations from the same cow. When milk nutrients were expressed on a mg per kcal basis, the pattern changes: CP, Ca, and P remained relatively constant over lactation on a per energy basis. Calf mass quadrupled over the first year of life; mass gain was linear at 0.9 kg/day. Asian elephant milk composition is variable, both across lactations and between cows, complicating efforts to determine representative values for comparative studies and for the formulation of elephant milk formulas. The fact that CP, Ca, and P were all relatively constant when expressed on a per energy basis may be of biological significance. The increase in nutrient density over lactation undoubtedly limits maternal water loss, reducing the volume of milk necessary to support the calf. Zoo Biol 32:291–298, 2013. © 2012 Wiley Periodicals, Inc.     

Recovery rates of bottlenose dolphin (Tursiops truncatus) carcasses estimated from stranding and survival rate data

Recovery of cetacean carcasses provides data on levels of human‐caused mortality, but represents only a minimum count of impacts. Counts of stranded carcasses are negatively biased by factors that include at‐sea scavenging, sinking, drift away from land, stranding in locations where detection is unlikely, and natural removal from beaches due to wave and tidal action prior to detection. We estimate the fraction of carcasses recovered for a population of coastal bottlenose dolphins (Tursiops truncatus), using abundance and survival rate data to estimate annual deaths in the population. Observed stranding numbers are compared to expected deaths to estimate the fraction of carcasses recovered. For the California coastal population of bottlenose dolphins, we estimate the fraction of carcasses recovered to be 0.25 (95% CI = 0.20–0.33). During a 12 yr period, 327 animals (95% CI = 253–413) were expected to have died and been available for recovery, but only 83 carcasses attributed to this population were documented. Given the coastal habits of California coastal bottlenose dolphins, it is likely that carcass recovery rates of this population greatly exceed recovery rates of more pelagic dolphin species in the region.     

To feed or not to feed? Bioenergetic impacts of fear‐driven behaviors in lactating dolphins

In mammals, lactation can be the most energetically expensive part of the reproductive cycle. Thus, when energy needs are compromised due to predation risk, environmental disturbance, or resource scarcity, future reproductive success can be impacted. In marine and terrestrial environments, foraging behavior is inextricably linked to predation risk. But quantification of foraging energetics for lactating animals under predation risk is less understood. In this study, we used a spatially explicit individual‐based model to study how changes in physiology (lactating or not) and the environment (predation risk) affect optimal behavior in dolphins. Specifically, we predicted that an adult dolphin without calf would incur lower relative energetic costs compared to a lactating dolphin with calf regardless of predation risk severity, antipredator behavior, or prey quality consumed. Under this state‐dependent analysis of risk approach, we found predation risk to be a stronger driver in affecting total energetic costs (foraging plus locomotor costs) than food quality for both dolphin types. Further, contrary to our hypothesis, after accounting for raised energy demands, a lactating dolphin with calf does not necessarily have higher relative‐to‐baseline costs than a dolphin without calf. Our results indicate that both a lactating (with calf) and non‐lactating dolphin incur lowered energetic costs under a risk‐averse behavioral scheme, but consequently suffer from lost foraging calories. A lactating dolphin with calf could be particularly worse off in lost foraging calories under elevated predation risk, heightened vigilance, and increased hiding time relative to an adult dolphin without calf. Further, hiding time in refuge could be more consequential than detection distance for both dolphin types in estimated costs and losses incurred. In conclusion, our study found that reproductive status is an important consideration in analyzing risk effects in mammals, especially in animals with lengthy lactation periods and those exposed to both biological and nonbiological stressors.