Variation in Growth and Potentially Associated Health Status in Hermann's and Spur‐Thighed Tortoise (Testudo hermanni and Testudo graeca)

Captive reptiles often show higher growth rates than in the wild, possibly due to higher feeding intensity. Although health problems are usually linked to inappropriate diets, fast growth itself, such as triggered by appropriate diets fed in high amounts, has traditionally also been considered unfavorable for tortoises. We document growth rates (based on age and mass) from private Testudo hermanni and T. graeca breeders, which are generally higher than those reported for free‐ranging specimens, but show enormous variation. Tortoise patients presented to an exotics clinic also covered the whole growth rate spectrum. To test whether fast growth was associated with diseases, the age–body mass relationship of these patients was tested, in a retrospective evaluation, for additional influence factors, such as dietary history and occurrence of certain diet and growth‐related diseases. No indication was found that animals particularly heavy for their age were more prone to diet/growth‐related disorders. In general, tortoises fed diets with meat/grain were heavier for their age than tortoises fed more appropriate diets; dietary history was not related to a particular disease. The results suggest the age–body mass relationship may not be suitable for testing effects of fast growth; an age–body length relationship would be more appropriate. Animals presented for a diet/growth‐related disorder were younger than animals presented for other reasons; there was a significant negative correlation between the severity of pyramiding and age, suggesting that growth‐related disorders may well limit the life expectancy of tortoises. Controlled clinical studies are required to fully test this hypothesis. Zoo Biol. 31:705‐717, 2012. © 2012 Wiley Periodicals, Inc.     

An Examination of Adult Women’s Sleep Quality and Sleep Routines in Relation to Pet Ownership and Bedsharing

ABSTRACT

People in many parts of the world commonly share their beds not only with human partners but also with dogs and cats. Self-report and actigraphy data have shown that sleeping with an adult human partner has both positive and negative impacts on human sleep, but there has been little exploration of the impacts that pets have on human sleep quality. We collected survey data online from 962 adult women living in the United States to investigate relationships between pet ownership and human sleep. Fifty-five percent of participants shared their bed with at least one dog and 31% with at least one cat. In addition, 57% of participants shared their bed with a human partner. Our findings did not show a strong relationship between pet ownership status or bedsharing conditions and sleep quality as assessed by the Pittsburgh Sleep Quality Index (PSQI), although according to this measure, a high percentage of study participants did experience sleep quality deficits. It is possible that pet ownership contributed to the high global PSQI scores we observed, especially since all but 7% of participants resided with dogs and/or cats. Other measures included in this study indicate that dogs and cats, and where they sleep, may indeed affect sleep habits and perceptions of sleep quality. Dog owners had earlier bedtimes and wake times than individuals who had cats but no dogs. Compared with human bed partners, dogs who slept in the owner’s bed were perceived to disturb sleep less and were associated with stronger feelings of comfort and security. Conversely, cats who slept in their owner’s bed were reported to be equally as disruptive as human partners, and were associated with weaker feelings of comfort and security than both human and dog bed partners. Follow-up research is necessary to determine if pet owners’ perceptions of pets’ impacts on their sleep align with objective measures of sleep quality.     

Reasons for Relinquishment of Companion Animals in U.S. Animal Shelters: Selected Health and Personal Issues

In personal interviews, people surrendering their dogs and cats to 12animal shelters in 4 regions of the country discussed their reasons for relinquishing their companion animals and answered questions about their own characteristics and those of their pet. The interviews identified 71 reasons for relinquishment. Personal issues lead the class of reasons for relinquishment of cats and ranked 3rd among those given for relinquishment of dogs. The top 3 health and personal issues cited for giving up cats were allergies of a family member to cats, owner's personal problems, and anew baby. For dogs, the top 3 reasons cited were lack of time for the dog, owner's personal problems, and allergies. Analysis of these health and personal issues suggests that education and counseling before and after acquisition of a pet, as well as the availability of temporary accommodations for pets during times of personal crisis, may reduce relinquishments.     

A Comparison of Attachment Levels of Adopters of Cats: Fee-Based Adoptions Versus Free Adoptions

Nonhuman animal welfare professionals have been critical of adoption programs that do not charge a fee for adult cats, despite the high euthanasia rate for cats due to a reported lack of homes. The argument against the free cat adoptions cites a devaluation of the cat, which may affect the adopter's perceived value of the cat and subsequent care. It may also attract low-income adopters who are perceived as unable to fulfill the financial responsibility of acting as caregiver (owner) of a companion animal (pet). This study examined adopters' attachment to their cats in relation to the payment or waiver of an adoption fee using the Lexington Attachment to Pets Scale and perception of the shelter. No significant differences were found between groups on either measure. Programs such as this create an opportunity to positively affect cats in animal shelters by finding more homes; programs such as this also affect cat overpopulation by putting more altered cats into the community.     

Attachment Anxiety and Avoidance Influence Pet Choice and Pet-directed Behaviors

Attachment theory is a useful lens through which to examine both perceptions and selection of companion animals. Study 1 compared perceptions of dogs and cats, and found that dogs were perceived as having more positive relationship qualities and secure attachment-related characteristics, whereas cats were perceived as having more negative relationship qualities and avoidant attachment-related characteristics. In addition, people perceived relationships with dogs to involve less avoidance and less anxiety relative to relationships with people. In study 2, which built on the findings of study 1, attachment avoidance was negatively associated with wanting to own a pet, whereas attachment anxiety was positive associated with wanting to own a pet. These attachment dimensions were not associated with wanting to own a dog, but lower avoidance and higher anxiety were associated with wanting to own a cat. Study 3 was a longitudinal study of SPCA-type shelter visitors (510 participants, with 169 reporting a recent pet adoption). Lower attachment anxiety predicted recently adopting a dog rather than a cat, though neither anxiety nor avoidance predicted adopting a cat. Individuals who wanted a pet in order to facilitate human relationships were more likely to adopt a dog than a cat. Those high in attachment avoidance reported turning to their pet as a replacement for human companionship, and those high in attachment anxiety reported feeling more concern about their pets requiring more attention. Attachment anxiety and avoidance may influence the decision whether or not to adopt a pet, as well as the motivation underlying the adoption choice. Attachment also may influence the type of pet chosen (i.e., dog versus cat). In addition, attachment may influence the nature of the human–animal relationship, such as the time spent together, and the security felt regarding the relationship.     

The effects of surimi and pelleted diets on the laboratory survival, growth, and feeding rate of the cuttlefish Sepia officinalis L.

The effects of feeding a prepared surimi diet (fish-based) and a prepared pelleted diet (shrimpbased) on the survival, growth and feeding rate of the cuttlefish Sepia officinalis L. were evaluated during a 45-day experiment. One hundred and twenty juveniles of laboratory cultured cuttlefish (74.5 ± 12.36 g) were divided into three treatments and were fed thawed shrimp (control), pellets or surimi. Survival rates on these diets were 95.0%, 67.5% and 22.5%, respectively. Preliminary data indicated that the low survival of cuttlefish fed surimi may have been caused by low levels of copper in their blood (131 vs 244 μg/ml) since copper is required for their respiratory blood pigment, hemocyanin. Instantaneous growth rates were 2.71 % body weight BW/day for cuttlefish fed raw shrimp, 0.33% BW/day for cuttlefish fed pellets, and 0.54% BW/day for cuttlefish fed surimi. The feeding rate of cuttlefish fed shrimp was high (6–8% BW/day). The feeding rate on pellets increased with time (from < 1 to 3% BW/day) but never reached the level for raw shrimp. The feeding rate on surimi increased to equal the rate for raw shrimp during days 1–30 (8 to 9% BW/day) and thereafter decreased (<4% BW/day). In conclusion, there was a major distinction between the palatability of a prepared diet and the ability of that diet to support growth. Surimi was highly palatable but resulted in poor survival, suggesting low nutritional quality. In contrast, pellets were less palatable but produced maintenance growth. Development of practical surimi diets will require supplementation of the surimi with soluble micro- and macronutrients.     

Vegetarian and Weight‐Loss Diets among Young Adults

Objective: Young adults frequently experiment with vegetarian and weight‐loss diets. Comparisons of their experiences on these two different diets may help in the development of approaches to improve long‐term adherence to weight‐loss regimens. In the current study vegetarian and weight‐loss diets were compared on how long and how strictly they were followed, and reasons why they were initiated and discontinued. Research Methods and Procedures: From 428 college students surveyed, four groups were delineated: 1) 59 participants had been following a vegetarian diet but not a weight‐loss diet (Vegetarian), 2) 117 participants had tried a weight‐loss diet but not a vegetarian diet (Weight Loss), 3) 133 participants had followed both a vegetarian and a weight‐loss diet (Both), and 4) 119 participants had not tried either diet (Neither). Results: Differences were examined by comparing the Vegetarian and Weight‐Loss groups as well as by comparing the two diets within the Both group. Duration of the vegetarian diet was much greater than the weight‐loss diet; most participants in the Vegetarian group (62%) remained on their diet for more than 1 year, whereas the majority of the Weight‐Loss participants (61%) followed their diet for 1 to 3 months. Similar results were found when comparing the two diets within the Both group. How strictly the two diets were followed, however, did not differ. Analyses revealed that reasons for discontinuing a diet varied; participants were more likely to cite boredom as a reason for discontinuing a weight‐loss diet than a vegetarian diet (53% vs. 5% between groups and 30% vs. 10% within the Both group). Discussion: The longer duration of the vegetarian diet relative to the weight‐loss diet warrants further investigation. Results could possibly be applied to behavioral weight‐loss treatment to improve long‐term maintenance.     

Effects of class-specific,synthetic, and natural proteinase inhibitors on life-history traits of the cotton bollworm Helicoverpa armigera

Herbivorous insects have more difficulty obtaining proteins from their food than do predators and parasites. The scarcity of proteins in their diet requires herbivores to feed voraciously, thus heavily damaging their host plants. Plants respond to herbivory by producing defense compounds, which reduce insect growth, retard development, and increase mortality. Herbivores use both pre- and postdigestive response mechanisms to detect and avoid plant defense compounds. Proteinase inhibitors (PIs) are one example of plant compounds produced as a direct defense against herbivory. Many insects can adapt to PIs when these are incorporated into artificial diets. However, little is known about the effect of PIs on diet choice and feeding behavior. We monitored the diet choice, life-history traits, and gut proteinase activity of Helicoverpa armigera larvae using diets supplemented with synthetic and natural PIs. In choice experiments, both neonates and fourth-instar larvae preferred the control diet over PI-supplemented diets, to varying degrees. Larvae that fed on PI-supplemented diets weighed less than those that fed on the control diet and produced smaller pupae. Trypsin-specific PIs had a stronger effect on mean larval weight than did other PIs. A reduction of trypsin activity but not of chymotrypsin activity was observed in larvae fed on PI-supplemented diets. Therefore, behavioral avoidance of feeding on plant parts high in PIs could be an adaptation to minimize the impact of this plant's defensive strategy.     

Using Gross Energy Improves Metabolizable Energy Predictive Equations for Pet Foods Whereas Undigested Protein and Fiber Content Predict Stool Quality

Because animal studies are labor intensive, predictive equations are used extensively for calculating metabolizable energy (ME) concentrations of dog and cat pet foods. The objective of this retrospective review of digestibility studies, which were conducted over a 7-year period and based upon Association of American Feed Control Officials (AAFCO) feeding protocols, was to compare the accuracy and precision of equations developed from these animal feeding studies to commonly used predictive equations. Feeding studies in dogs and cats (331 and 227 studies, respectively) showed that equations using modified Atwater factors accurately predict ME concentrations in dog and cat pet foods (r² = 0.97 and 0.98, respectively). The National Research Council (NRC) equations also accurately predicted ME concentrations in pet foods (r² = 0.97 for dog and cat foods). For dogs, these equations resulted in an average estimate of ME within 0.16% and 2.24% of the actual ME measured (equations using modified Atwater factors and NRC equations, respectively); for cats these equations resulted in an average estimate of ME within 1.57% and 1.80% of the actual ME measured. However, better predictions of dietary ME in dog and cat pet foods were achieved using equations based on analysis of gross energy (GE) and new factors for moisture, protein, fat and fiber. When this was done there was less than 0.01% difference between the measured ME and the average predicted ME (r² = 0.99 and 1.00 in dogs and cats, respectively) whereas the absolute value of the difference between measured and predicted was reduced by approximately 50% in dogs and 60% in cats. Stool quality, which was measured by stool score, was influenced positively when dietary protein digestibility was high and fiber digestibility was low. In conclusion, using GE improves predictive equations for ME content of dog and cat pet foods. Nondigestible protein and fiber content of diets predicts stool quality.     

Evaluation of nutrient digestibility and fecal characteristics of exotic felids fed horse‐ or beef‐based diets: use of the domestic cat as a model for exotic felids

The objective of this study was to determine the effects of feeding commercially available beef‐ and horse‐based diets on nutrient digestibility and fecal characteristics of large captive exotic felids and domestic cats. Four species of large exotic felids including cheetahs, Malayan tigers, jaguars, and Amur tigers, and domestic cats were utilized in a crossover design. Raw meat diets included a beef‐based diet (57% protein; 28% fat) and a horse‐based diet (51% protein; 30% fat). All cats were acclimated to the diet for 16 days followed by a 4 day collection period, where total feces, including one fresh sample, were collected. All feces were scored on collection. Intake did not differ due to diet, but fecal output was greater when cats consumed the horse‐based diet. Total tract apparent dry matter (DM) digestibility was higher (P<0.05) and organic matter (OM) and crude protein (CP) digestibilities were lower (P<0.05) when cats were fed the beef‐based diet compared with the horse‐based diet. CP digestibility was similar in domestic cats and cheetahs, and greater (P<0.05) than Amur tigers. Fecal scores were lower and fecal DM was greater (P<0.05) when cats consumed the horse‐based diet compared with the beef‐based diet. Domestic cats had lower (P<0.05) fecal ammonia concentrations compared with all other species. Fecal ammonia concentrations were lowest (P<0.05) when cats were fed the horse‐based diet. Fecal total short‐chain fatty acid (SCFA), branched‐chain fatty acid (BCFA), and butyrate concentrations were higher (P<0.05) when cats consumed the beef‐based diet. Our results suggest that the domestic cat serves as an appropriate model for large exotic felid species, but differences among the species exist. Decreased nutrient digestibility by tigers and jaguars should be considered when developing feeding recommendations for these species based on domestic cat data. Zoo Biol 29:432–448, 2010. © 2009 Wiley‐Liss, Inc.     

Diet of chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda, 1. Diet composition and diversity

Chimpanzees (Pan troglodytes) are ecologically flexible omnivores with broad diets comprising many plant and animal foods, although they mostly eat fruit (including figs). Like other ecologically flexible nonhuman primates (e.g., baboons, Papio spp.) with broad diets, their diets vary across habitats. Much data on diets come from short studies that may not capture the range of variation, however, and data are scant on variation within habitats and populations. We present data on diet composition and diversity for chimpanzees at Ngogo, in Kibale National Park, Uganda, collected over a 15-year period, with a focus on the plant components of the diet. We compare Ngogo data to those on chimpanzees at the nearby Kibale site of Kanyawara, on other chimpanzee populations, and on some other frugivorous-omnivorous primates. Results support the argument that chimpanzees are ripe fruit specialists: Ngogo chimpanzees ate a broad, mostly fruit-based diet, feeding time devoted to fruit varied positively with fruit availability, and diet diversity varied inversely with fruit availability. Comparison of Ngogo and Kanyawara shows much similarity, but also pronounced within-population dietary variation. Chimpanzees fed much more on leaves, and much less on pith and stems, at Ngogo. Figs accounted for somewhat less feeding time at Ngogo, but those of Ficus mucuso were quantitatively the most important food. This species is essentially absent at Kanayawara; its abundance and high productivity at Ngogo, along with much higher abundance of several other important food species, help explain why chimpanzee community size and population density are over three times higher at Ngogo. High inter-annual variation at Ngogo highlights the value of long-term data for documenting the extent of ecological variation among chimpanzee populations and understanding how such variation might affect population biology and social dynamics.     

Population dynamics, overpopulation, and the welfare of companion animals: new insights on old and new data

Americans profess a great love for their companion animals, and, indeed, their expenditures on food and other products for their dogs and cats would seem to confirm this. However, each year, many millions of dogs and cats are brought to animal shelters, where the majority are euthanized. Our inability to provide reasonably valid statistics related to this concern makes it difficult to offer a credible presentation on the need for a concerted effort to deal with the issue, design initiatives to ameliorate the problem, or evaluate progress and performance of these efforts. In this article we review some of the past efforts to document the scale of the “pet overpopulation ”problem. We reexamine long-term shelter statistics from a single shelter system and present new data that reflect a recent cooperative effort to understand the origins and disposition of dogs and cats received by animal shelters.     

Why Do People Feed Free-roaming Cats? The Role of Anticipated Regret in an Extended Theory of Planned Behavior in Malaysia

Free-roaming cats are common in residential and public areas in Malaysia and approach people for food. However, the psychological determinants of public feeding are unknown. This study investigated public perceptions of feeding free-roaming cats, based on an extended theory of planned behavior (TPB). It consisted of qualitative belief-elicitation interviews with 25 participants, followed by a quantitative survey of 167 participants, representative of the country’s population. The majority (87.2%) of the sample had fed free-roaming cats. The mean intention score (4.88 out of 7) indicated the public was likely, and would make an effort, to feed free-roaming cats in the future. The public’s benevolence toward animals largely explained the findings, based on generally positive attitudes and perceptions of moderate social credence and capability and confidence, underpinned by affective and cognitive beliefs. An important finding was the role of anticipated regret in predicting and explaining intentions, which contributed variance over and above that explained by the TPB constructs. The extended framework is explained by the influence of anticipated regret on the perceived evaluation of potential TPB outcomes, which in turn leads to the behavior becoming less volitional. Therefore, future TPB studies of people’s interactions with animals, such as free-roaming cats, should take account of affective and emotional antecedents of behavior, such as anticipated regret, to improve explanatory power. The study also has implications for managing public feeding of free-roaming cats, such as drawing on and strengthening the Malaysian public’s positive attitudes and emotional concern to redirect current feeding practices toward more constructive animal welfare initiatives. Such humane approaches align with the public’s sensitivity toward animal welfare and the historical development of cat population control from lethal methods to humane non-lethal methods to ensure adequate care.     

Characteristics of Shelter-Relinquished Animals and Their Owners Compared With Animals and Their Owners in U.S. Pet-Owning Households

Animal shelters in the United States annually receive millions of relinquished dogs and cats, and risk factors for relinquishment are not fully understood. Investigators sponsored by the National Council on Pet Population Study and Policy interviewed people who relinquished dogs and cats at 12 shelters in four regions. We collected similar data from a sample of U.S. households with companion animals. Data collected included nonhuman animal characteristics such as age, sex, and frequency of selected behaviors. We also obtained data on keepers' (owners') age, sex, and level of education as well as their general knowledge of pet care and behavior. We found that relinquishment was associated with physical and behavioral characteristics of the animals and owner characteristics and knowledge. Relinquished animals were more likely to be intact, younger, and mixed bred. People relinquishing animals were significantly more likely to be men and younger than 35 years. Duration of ownership was significantly shorter for relinquished animals.     

Development of probiotic diets for the olive fly: evaluation of their effects on fly longevity and fecundity

One possible control strategy against the olive fly, Bactrocera oleae, the most serious olive crop pest, is the Sterile Insect Technique (SIT) application. However, a number of problems associated with this method remain that decrease the effectiveness of SIT, including the quality of reared insects. Taking the importance of the relationship between the olive fly and bacteria into consideration, the effects of probiotic diets enriched with Pseudomonas putida on B. oleae longevity and fecundity were evaluated. First, we found that the probiotic bacterium, P. putida, is conveyed from diets to the oesophageal bulb as well as to the fly midgut after feeding on the probiotic diet. Subsequently, B. oleae adults fed on either: (a) a standard full protein and sugar diet; (b) a sugar only diet; (c) a probiotic standard full protein and sugar diet; or (d) a probiotic sugar diet. Flies fed on probiotic diets were supplied with an inoculated gel containing P. putida; non‐inoculated gel was provided to the flies fed on non‐probiotic diets. B. oleae males and females that fed on sugar diets did not survive as long as those that fed on protein diets. A comparison of the longevity of adults fed on full diet and sugar with their respective probiotic diets revealed no significant difference. Males fed on the sugar only diet survived longer than males fed on probiotic sugar diet, and females fed on the full protein and sugar diet survived much longer than females fed on the full probiotic diet. As regarding fecundity, both full diets resulted in a higher number of eggs laid per female. Females fed on the probiotic sugar diet laid a higher number of eggs than females that fed on sugar only. The inoculated gel of the probiotic sugar diet contained a significantly higher quantity of leucine, isoleucine and proline than the non‐inoculated gel of the sugar only diet. The possible role of dietary bacteria in relation to functional aspects of olive fly physiology is discussed.     

Carnivorous mammals: nutrient digestibility and energy evaluation

Estimating the energy content is the first step in diet formulation, as it determines the amount of food eaten and hence the concentration of nutrients required to meet the animal's requirements. Additionally, being able to estimate the energy content of a diet empirically known to maintain body condition in an animal will facilitate an estimation of maintenance energy requirements. We collated data on nutrient composition of diets fed to captive wild canids, felids, hyenids, mustelids, pinnipeds, and ursids and the digestibility coefficients from the literature (45 species, 74 publications) to test whether differences in protein and fat digestibility could be detected between species groups, and whether approaches suggested for the estimation of dietary metabolizable energy (ME) content in domestic carnivores (NRC [2006] Nutrient requirements of dogs and cats. Washington, DC: National Academy Press.) can be applied to wild carnivores as well. Regressions of digestible protein or fat content vs. the crude protein (CP) or fat content indicated no relevant differences in the digestive physiology between the carnivore groups. For diets based on raw meat, fish, or whole prey, applying the calculation of ME using “Atwater factors” (16.7 kJ/g CP; 16.7 kJ/g nitrogen‐free extracts; 37.7 kJ/g crude fat) provided estimates that compared well to experimental results. This study suggests that ME estimation in such diets is feasible without additional digestion trials. For comparative nutrition research, the study implicates that highly digestible diets typically fed in zoos offer little potential to elucidate differences between species or carnivore groups, but research on diets with higher proportions of difficult‐to‐digest components (fiber, connective tissues) is lacking. Zoo Biol 29:687–704, 2010. © 2010 Wiley‐Liss, Inc.     

Simultaneous estimation of diet composition and calibration coefficients with fatty acid signature data

Knowledge of animal diets provides essential insights into their life history and ecology, although diet estimation is challenging and remains an active area of research. Quantitative fatty acid signature analysis (QFASA) has become a popular method of estimating diet composition, especially for marine species. A primary assumption of QFASA is that constants called calibration coefficients, which account for the differential metabolism of individual fatty acids, are known. In practice, however, calibration coefficients are not known, but rather have been estimated in feeding trials with captive animals of a limited number of model species. The impossibility of verifying the accuracy of feeding trial derived calibration coefficients to estimate the diets of wild animals is a foundational problem with QFASA that has generated considerable criticism. We present a new model that allows simultaneous estimation of diet composition and calibration coefficients based only on fatty acid signature samples from wild predators and potential prey. Our model performed almost flawlessly in four tests with constructed examples, estimating both diet proportions and calibration coefficients with essentially no error. We also applied the model to data from Chukchi Sea polar bears, obtaining diet estimates that were more diverse than estimates conditioned on feeding trial calibration coefficients. Our model avoids bias in diet estimates caused by conditioning on inaccurate calibration coefficients, invalidates the primary criticism of QFASA, eliminates the need to conduct feeding trials solely for diet estimation, and consequently expands the utility of fatty acid data to investigate aspects of ecology linked to animal diets.     

Food intake, conversion efficiency, and feeding behaviour of tobacco hornworm caterpillars given artificial diet of varying nutrient and water content

ABSTRACT Fifth stadium tobacco hornworm caterpillars, Manduca sexta (L.), given artificial diet diluted to varying extents with either cellulose or water compensated for the food's reduced nutrient content by eating more of it. This compensation was, however, in most cases not sufficient to maintain normal growth rates. When the water content of the diet was reduced, the insects ate less than the usual fresh weight of food but maintained their intake of nutrients. Nevertheless, growth rate was impaired. The insects were better able to compensate for dilution of their food with water than with cellulose. The efficiency of conversion of ingested food (ECI) was decreased when the diet was adulterated with cellulose. At moderate dilution (50% nutrient) this was due mostly to decreased approximate digestibility (AD), but at greater dilution (25% and 10% nutrient content) the efficiency of conversion of digested food (ECD) was decreased. ECI was maintained when the water content of the diet was increased to give 50% nutrient concentration, but was decreased when water content was changed more radically (200%, 25% and 10% nutrient diets). This was due mostly to increased metabolic costs (decreased ECD) in all cases. The retention time of food in the gut was progressively decreased (i.e. speed of passage was increased) as nutrients were replaced by cellulose. By contrast, dilution of the diet with water resulted in only slight changes in retention time, except at extreme dilution (10% nutrient content) when retention time was reduced. Compensation of food intake was achieved by spending more (or less) time eating. Video analysis of feeding behaviour showed that there were significant changes in the length of feeding bouts and of interfeed gaps when caterpillars fed on diets of altered composition. For diets diluted with cellulose, changes in bout length and bout frequency contributed substantially to the increased time spent feeding on the adulterated food. For diets diluted with water, however, almost all of the compensatory change in behaviour was due to increased bout length, with bout frequency affected only slightly. This suggests that volumetric feedback contributes principally to the termination of feeding bouts in caterpillars, while nutrient flow may affect both the initiation and termination of feeding.     

Acorns,insects, and the diet of adult versus nestling Acorn Woodpeckers

ABSTRACT The diet of Acorn Woodpeckers (Melanerpes formicivorus) in central coastal California consists of a mixture of high‐quality (insects) and low‐quality (stored acorns) food during the spring breeding season. We used stable isotope ratios obtained from blood samples to estimate possible differences in the proportion of these items being fed to nestlings and being consumed by breeding adults, as well as the extent to which the diet of nestlings shifts between insects and acorns during the nestling period. Based on both feeding observations and items recovered from nestlings, older nestlings were fed 28% acorns. Using this value as a baseline for the isotope analyses, the diet of breeding adults was estimated to consist of 90% acorns. Based on repeated samples from the same nestlings over time, the estimated proportion of acorns in their diet increased from 19% in 9‐ to 12‐d‐old nestlings to 42% in 23‐ to 26‐d‐old nestlings. There was a significant correlation between the isotope values of adults and the nestlings they fed, indicating that different groups of Acorn Woodpeckers have significantly different diets. Although important for successful reproduction in this species, stored acorns are not the primary food resource used to feed young. Instead, the availability of stored acorns allows adult Acorn Woodpeckers to provide nestlings with more protein‐rich insects while maintaining themselves on relatively protein‐poor, low‐quality acorns. Differences in the diets of adults and their nestlings are likely widespread among species that feed, at least in part, on low‐quality foods, such as fruit and seeds, during the breeding season.