Fruit Bat Nutrition Guide

Written by Zutrition . Posted in Diet, Mammals

Spectacled Flying Fox

Spectacled flying fox (Pteropus conspicillatus)

Photo Credit: Mnolf, Wikimedia Commons

This document is meant to serve merely as a guideline for zoo professionals feeding captive fruit bats.  This document is excerpted entirely from the Nutrition Advisory Group Handbook, Fruit Bats, Nutrition and Dietary Husbandry, By Janet L. Dempsey, MS.  The complete document can be viewed at this link.

Fruit Bat Nutrition Guide

The frugivorous and nectarivorous bat species found in the families Pteropodidae (Megachiroptera) and Phyllostomidae (Microchiroptera) have been maintained in captivity with the greatest success, due in large measure to their preferences for soft, sweet fruits and the ability of zoos to satisfy those preferences with adequate diets.

Diets for captive fruit bats have traditionally been based on feeding habits in the wild. Studies on wild bats include attempts to collect and analyze food items that they have been observed eating and to identify foods consumed through examination of fecal or stomach contents.23,30,42,48,57,65,70,74

These data, while important, are not sufficient to set nutrient requirements, and the specific nutrient needs of frugivorous and nectarivorous bats remain virtually unknown.

The studies of nutrient requirements that have been conducted and diets that have been successfully used in captivity are discussed below.

 

Grey headed flying fox

Grey-headed Flying Fox (Pteropus poliocephalus) with baby. There’s also a Little red flying-fox (Pteropus scapulatus) on the left

Photo Credit: Mnolf Wikimedia Commons

Digestive Tract Morphology and Physiology

Fruit bats are highly efficient in extracting the liquid portion of chosen foods. They have fewer teeth than insectivores,10 and their teeth are broad and relatively flat for crushing fruits, allowing the bats to squeeze out and swallow the juices.23 The fibrous portion remaining is much reduced in moisture and is spit out in tightly compressed pellets (ejecta). Seeds also may be swallowed, but many of those from figs appear to pass whole into the feces.23,48 To meet nutrient needs, daily food intakes (on a wet basis) range as high as 2.5 times body mass.14,15,16,26,31,48,63,70 These large volumes of food are processed through the digestive tract rapidly, with transit times ranging from 15-100 min.

Nutrient Content of Foods

Upon comparison with established nutrient requirements of other mammals and the foods needed to provide them, fruit, when consumed alone, would seem to constitute an inadequate diet. Analyses of most cultivated fruits indicate that the concentrations of many nutrients are quite low. However, there are few documented analyses of the nutrients in wild fruit species, and A. jamaicensis (Jamaican fruit bat) has been reported to feed on fruits from over 70 genera.23  Thus, it may be important to distinguish between cultivated and wild fruits. Limited compositional data on proximate fractions and minerals in both are presented in the Table below. The cultivated fruits listed tend to be lower in fiber, ash, and calcium (dry basis), with some higher in moisture, than the listed wild fruits.8,19,25,31,59,60,66  Comparisons between cultivated and wild fruits in concentrations of vitamins could not be made because published vitamin values for wild fruits were not found.

Comparison of the mineral content of cultivated and native fruits

   

Expressed on a dry matter basis

Fruit Type

Moisture

Ca

P

Fe

Se

%

%

%

ppm

ppm

Cultivateda,b          
Apple 84.50 0.03 0.05 4.5 0.02
Banana 74.30 0.02 0.08 11.9 0.04
Cantaloupe 89.78 0.11 0.17 21.5 0.04
Orange 86.80 0.30 0.11 7.6 0.04
Native          
Fig (F.pertusa)c
Ripe fruit 77.20 0.74 0.12 56.6 0.03
Fig (F.trigonata)c
Unripe fruit 83.70 0.74 0.23 49.9 0.10
Fig (Belize native)d 72.08 2.04 0.18 58.1
Fig (Indonesia native)e 1.21 0.33 65.7
Fig (Uganda native)e 1.52 0.18 94.7
  • a. Data from Pennington and Church. 60
  • b. Fruit without skin or peel, includes seeds.
  • c. Data from Edwards. 19  N=3 for F. pertusa, N=1 for F. trigonata.
  • d. Data from Silver et al. 66   Samples were pooled from multiple Ficus sp., N=5.
  • e. Data from O’Brien et al. 59 Indonesia N=20, Uganda N=10.

Fruit bats in the wild appear to meet their nutrient needs by consuming large quantities of a mixture of native fruits, with some consumption of flower parts, leaves, and insects.2,11,12,21,23,28,33,34,36,37,38,46-49,61,78 In captivity, fruit sources are limited to those that are cultivated and readily available. As a consequence, it may be important to ensure that all essential nutrients are supplied by using other nutritionally complete foods. To formulate such foods, it is important to know which nutrients are essential to fruit bats and in what amounts they should be supplied.

Nutrient Requirements

Despite differences in diet and feeding strategy among mammals, most species that have been studied appear to have similar qualitative nutrient needs for normal tissue metabolism. Presumably, these similarities also apply to fruit bats. Approximately fifty nutrients have been identified as dietary essentials for mammals. That is, they must be obtained from the diet or through the activity of gastrointestinal microbes because they cannot be endogenously synthesized in quantities appropriate to meet animal needs.

Water

Water is the easiest and least expensive nutrient to provide in captivity. A supply of water is crucial due to its involvement in a variety of essential functions within the body. The need for liquid water is influenced by variables such as ambient air temperature and humidity, solar and thermal radiation, metabolic rates, and food composition and intake.64 Many species have been observed to actively consume water both in captivity and in the wild. Wild species of Pteropus on oceanic islands have been observed consuming sea water, and their kidneys appear well-adapted to excreting salt.29 Therefore, considering the limited food choices and, in some cases, fluctuating environmental conditions, it is prudent to provide ad libitum access to fresh water in captivity.

 

Baby Grey Headed Flying Fox

A crib full of 2-3 week old baby Grey-headed Flying-foxes in care of Wildcare Australia at The Bat Hospital.

Photo Credit: Wikimedia Commons

Protein and amino acids

Fruit, as the only food item, is considered by many researchers to constitute an inadequate diet because of its low protein content when compared to other plant and animal food sources, although the quality of that protein is relevant to such a conclusion. It has been argued that both pteropodid and phyllostomid fruit bats must supplement their fruit diets with relatively higher protein items, including a more complementary array of amino acids, such as might be found in insects,48 pollen,35 or leaves32,33,38,78 in order to meet protein needs. However, other researchers maintain that fruit bats can meet their protein requirements exclusively with fruits.9,15,26,67,70

It was suggested that fruit bat species may vary in their foraging strategy, with some relying almost entirely on fruits throughout the year, whereas others may switch to insects when fruits are less abundant.

Energy

Fruit bats presumably have no difficulty meeting energy needs during periods of food abundance because they consume large amounts of high carbohydrate fruits, both in captivity and in the wild. There is controversy among researchers whether or not fruit bats must “over-ingest” energy in order to meet protein requirements. This is due to the relatively high energy:protein ratio of most fruits. High food (and energy) intakes were necessary to meet protein needs in pteropodids (Epomops buettikoferiMicropteropus pusillus, and Pteropus poliocephalus) when fed some low-protein fruits but not when fed others.67,70 Carollia perspicillata (phyllostomids) did not need to consume excessive energy to meet maintenance protein needs if appropriate wild foods were available and selected.

Estimates of metabolizable energy requirements for adult maintenance of A. jamaicensis have been made by a number of researchers, and range from 12 to 34.3 kcal/day.(15,48,63) The intermediate value of 17.2 kcal/day found by Reiter (63) is equivalent to 43.9 kcal of metabolizable energy/100 g body mass/day (mean body mass 39.2 g) or a metabolizable energy density in ingested dry matter of 3.16 kcal/kg, a metabolizable energy concentration found in many domestic fruits

Estimates of metabolizable energy requirements for adult maintenance of C. perspicillata weighing 18.5 g were 16.1 kcal/day/bat(14) and were 40.1 kcal/day for R. aegyptiacus with a mean body mass of 144 g,(31) or 76.3 to 91.9 kcal/day for R. aegyptiacus with a mean body mass of 156.7g.(15)

Care must be taken when interpreting published data on energy requirements of fruit bats because species, experimental diets, and levels of permitted activity varied appreciably among studies.

Basal energy expenditures of bats appear to vary with species (particularly body mass and foraging and roosting behavior), sexual dimorphism in body mass, precision of body temperature regulation, tendency to enter torpor, and the environmental circumstances within which they evolved.40,41 In addition, both dietary digestibility and metabolizability have usually been estimated rather than directly determined.

Some fruit bats eating very low protein diets may consume large amounts of food to meet protein requirements, thus elevating energy intakes. Researchers generally have noted little change in body mass, but studies of changes in body composition appear not to have been made. With respect to energy needs for flight, requirements are surely higher than for resting, and the amount of flight activity required in the wild will vary with food abundance and distribution. In captivity, it is likely that energy requirements for resting and for flight can be met by offering ad libitum quantities of nutritionally appropriate food.

 

Essential fatty acids

Apart from serving as sources of dietary energy and promoting fat-soluble vitamin absorption, fats also provide essential fatty acids (n-6 and n-3 series). The most important dietary fatty acids for the mammal species that have been studied are n-6 fatty acids, such as linoleic and arachidonic, and n-3 fatty acids, such as a-linolenic and longer chain fatty acids in this series. Qualitative requirements for essential fatty acids have been demonstrated in a number of mammalian species although quantitative requirements are mostly undefined.

Fruit bats are likely to have dietary fatty acid requirements similar to other mammals.

The recommendation for most mammals is to include essential fatty acids in the diet at 1-2% of the total metabolizable energy intake, with linoleic acid comprising the largest proportion of the total. However, the amounts of total essential fatty acids and the proportions of each may vary with species, age, and physiologic state.64,72 Cultivated fruits generally have very low levels of fat and essential fatty acids.60,73

Essential fatty acid concentrations in the wild fruits eaten by bats are largely unknown.

Vitamins and minerals

Specific vitamin and mineral requirements have not been determined for fruit bats, and there is no information on the nutrient requirements of their closest taxonomic relatives.

As a consequence, until specific requirements are determined, diets for captive bats may be presumed sufficient if formulated to provide bioavailable(1) vitamin and mineral levels within the ranges of nutrients for the listed laboratory species. It is known that some bat species lack the ability to synthesize vitamin C and therefore require a dietary source.3

Qualitative information on some vitamin and mineral requirements of fruit bats is available from observations of deficiencies or toxicities in captivity. Methodology must be carefully considered when interpreting the quantitative implications of such results. One report has described dilated cardiomyopathy in pteropodid fruit bats as a result of hypovitaminosis E.24 Hemochromatosis (iron storage disease) has been reported in three species of pteropodid fruit bats (Rousettus aegyptiacusPteropus giganteus, and P. poliocephalus), and was ascribed to dietary iron overload.13 The diet contained 400 mg of iron/kg of dry matter, by analysis. The principal unintended iron source was monodicalcium phosphate, which was used as a phosphorus supplement and contained 11,860 mg iron/kg.

Unusually high vitamin C supplementation (estimated intake of 7,500 mg/kg dry diet) may have compounded the problem by enhancing iron uptake.44,45 Studies of hematologic values and iron status of wild and captive fruit bats (Rousettus aegyptiacus) found lower plasma iron concentrations in wild (175 ng/dl) than in captive (286-316 ng/dl) subjects.

Investigators studying the cause of nodular bone lesions in the same three species of pteropodid fruit bats proposed fluoride toxicity as the probable cause.18 The diet contained shrimp meal, which is naturally high in fluoride, dicalcium phosphate, which may contain significant fluoride if a fertilizer-grade rather than a feed-grade product is used, fruit, and other supplements. Although the concentration of fluoride in the total diet was not reported, the estimated amounts of fluoride consumed by the bats were well above maximum tolerable levels reported for other species.51

Recently, several more cases of suspected fluoride toxicosis have been reported in pteropodid species (six Pteropus rodricensis, one Rousettus aegyptiacus) at one institution.71 The affected bats exhibited periosteal hyperostosis of long bones, similar to the previous study, as well as curled phalanges. The fluoride concentrations (by analysis) of all dietary items and water sources, as well as other potential sources of fluoride contamination (e.g., exhibit rock-work, flooring, and heating system condensate) were well below maximum tolerable levels for domestic species. Signs of periosteal hyperostosis were not seen after municipal tap water was replaced by distilled water for drinking.71 Quantitative fluoride requirements have not been established for most species. However, excessive levels have been shown to cause bone and tooth lesions, anorexia, lameness, necrosis of gastrointestinal mucosa, and cardiac failure.51 The results of these studies are not conclusive since requirements and tolerances of bats for fluoride have not been established.

Diets for Captive Frugivorous and Nectarivorous Bats

When formulating diets for captive fruit bats, foods available and appropriate for meeting probable nutrient needs must be identified. Bats that are primarily frugivorous or primarily nectarivorous are commonly fed similar diets. Nutritionally complete nectar formulas are sometimes included in diets for species that consume large amounts of nectar in the wild. Cultivated fruits are readily accepted by both groups. However, the concentrations of several nutrients in cultivated fruits are typically low or imbalanced, and an additional food source must generally be provided to ensure that nutrient concentrations in the total diet will be within the range required by other non ruminant mammalian species.50,53-56

The preferred method for ensuring dietary adequacy is to provide nutritionally complete feeds such as low-fiber, dry primate diets or dry diets formulated for frugivorous birds. These feeds should be formulated to meet the currently known requirements of the species for which they have been designed. The use of individual vitamin and mineral compounds as nutrient supplements is not recommended unless they are provided in a preparation specifically formulated for fruit bats. Over- or under-dosing, when using individual vitamin or mineral supplements, is common, as are the consequent toxicity and/or deficiency signs.

The nutritionally complete feed used should be as finely ground as possible to promote adequate consumption. Mixing fruit nectars, such as peach or apricot, with the ground feed will soften and/or suspend the diet and encourage intake, since fruit bats tend to be attracted to fruit nectars. Fruit also may be added to this mixture. However, it is advisable to chop the fruit into very small pieces or to mix ingredients in a blender so bats cannot preferentially consume fruit only. Because this mixture may gel if not mixed correctly and will ferment in a hot environment, its condition should be assessed periodically and the mixture replaced when necessary.

Behavioral enrichment in the form of hanging whole fruits may be used to encourage natural feeding behavior, providing fruit intakes relative to intakes of the complete diet are carefully monitored and are not excessive.

Microchiropteran and megachiropteran fruit bats are sometimes offered insects in addition to fruit, nutritionally complete feeds, and nectar formulas. A number of “home made” nectar formulas used successfully in captivity have been previously described.62 However, these formulations contain a variety of supplements that can be dangerous if misused. Nutritionally complete nectar powders formulated for hummingbirds are currently available with varying protein concentrations and may be appropriate for nectarivorous bats. Megachiroptera also are sometimes offered leafy vegetables and browse, both of which are readily accepted.34,36,37 Preliminary research suggests that certain browses are consumed preferentially,32,33,38 but the reasons for these choices are not entirely clear.2

The total diet should be formulated so that the items consumed will provide the probable nutrient requirements. Formulas and nutrient specifications for three diets that have been used successfully for 5 years, with generally minor modifications, are shown in the Table  below.

Formulas of and calculated nutrient concentrations in three sample fruit bat diets

Percent by weight, as fed

Ingredient

Diet Aa

Diet Bb

Diet Cc

Fruits, wholed

5.2

42.0

Fruits, choppedd

30.5

13.2

17.0

Vegetables, choppede

7.3

1.65

1.0

Starchy vegetables, choppedf

2.0

1.65

2.0

Leafy green vegetables, choppedg

10.4

7.0

PMI Prolab High Protein monkey diet 5045h

13.7

2.99

Marion Jungle Biscuiti

22.0

Calcium phosphate, dibasic

0.30

0.41

Peach nectar, canned

6.0

38.1

22.0

Orange juice, frozen, reconstituted

6.0

Water

18.6

29.0

100%

100%

100%

Nutrient

Calculated Concentration, DM basis

Dry matter, %

25.2

20.6

29.0

Crude protein, %

16.2

6.5

18.3

Crude fat, %

3.8

1.8

6.4

Vitamin A, IU/kg

23,419

6,240

10,484

Vitamin D3, IU/kg

3.595

958

2,877

Vitamin E, mg/kg

49

20

252

Vitamin C, mg/kg

588

752

444

Thiamin, mg/kg

10.6

4.0

6.5

Riboflavin, mg/kg

6.2

3.2

7.8

Niacin, mg/kg

72

32

59

Pantothenic acid, mg/kg

37

15

21

Vitamin B6, mg/kg

12

8

9

Folic acid, ug/kg

6,144

1,907

4,458

Biotin, ug/kg

>103

>28

>301

Vitamin B12, ug/kg

26

7

23

Choline, mg/kg

>980

>261

>1,079

Calcium, %

0.85

0.63

0.85

Phosphorous, %

0.61

0.52

0.58

Magnesium, %

0.17

0.09

0.15

Sodium, %

0.19

0.06

0.21

Potassium, %

1.16

0.90

0.84

Iron, mg/kg

411

352

140

Copper, mg/kg

14

7

15

Manganese, mg/kg

84

30

38

Zinc, mg/kg

90

29

78

Iodine, mg/kg

0.98

0.26

>0.8

Selenium, mg/kg

0.13

0.05

0.28

  • a. Fed to Rodriquez fruit bats (Pteropus rodricensis) at Brookfield Zoo for 5 years (Ca Phos,. Dibasic, added at 3yr).
  • b. Fed to Neotropical fruit bats (Artibeus jamaicensis) at Brookfield Zoo for 5 years.
  • c. Fed to Rodriguez fruit bats (Pteropus rodricensis) at Philadelphia Zoo for 5 years.
  • d. Whole fruits include apple, banana and orange; chopped fruits include apple, banana, blueberries, currants, grapes, mango and raisins
  • e. Vegetables (nonstarchy type) consisted of carrots, either steamed or raw.
  • f. Starchy vegetables consisted of sweet potatoes, either steamed or raw.
  • g. Leafy green vegetables included celery, romaine lettuce, and spinach.
  • h. Purina Mills, LLC, 1401 S. Hanley Rd., St. Louis, MO 63144 (800-227-8941)
  • i. Marion Zoological Inc., 2003 E. Center Circle, Plymouth, MN 55441 (800-327-7974)

Summary

Although specific nutrient requirements for frugivorous and nectarivorous bats remain virtually unknown, information exists which provides practical guidelines for formulating diets for captive bats. This information must be reviewed critically, applied sensibly, and compared with what is known for other mammalian species until more specific research is conducted. Opportunities for research in bat nutrition abound and, in view of the diversity of species, the information derived would improve not only our understanding of the nutrient requirements and dietary husbandry of bats but also of other species with similar dietary habits and feeding strategies.

References:

Nutrition Advisory Group Handbook, Fruit Bats, Nutrition and Dietary Husbandry, Author: Janet L. Dempsey, MS, Nestle Purina, Checkerboard Square, St. Louis, MO 63164 USA

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