Observations on the Feeding Capacities and Excretory Functions of Captive Vampire Bats

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Abstract
Observations are presented on the feeding capacities of captive vampire bats (Desmodus rotundus) and on their excretory functions as these relate to the volume of blood ingested and the metabolic efficiency of blood utilization. The average daily intake of blood by individual members of two large groups of bats in which consumption records were kept for a full year was 15.3 ml and 15.6 ml; the range of variation was between 11.6 and 21.0 ml. The daily consumption average of isolated individuals tended to be somewhat higher. One non-pregnant female maintained in isolation for 17 days consumed blood in excess of her body weight (28 gm ) on 13 of them, and on two days the amounts ingested were as high as 47 and 52 ml respectively. Urine excretion is copious, and generally amounts to slightly less than 50 per cent by volume of the blood ingested over a 24 hour period. Urine flow begins promptly after feeding, and evidence is presented that the tubular stomach is a major site of fluid absorption. Based upon observation of a single bat over a 4-day period it is estimated that the animal ingested (on a dry weight basis) an average of 0.12 gm solids/gm body weight per day, and “utilized” metabolically about 73% of the solids ingested. Justification is presented for our estimate (probably conservative), that under natural conditions a single vampire may ingest nearly two gallons of blood a year, and that the total blood lost by the animal prey of vampires in countries (such as Mexico) where the bats are common may amount to many hundreds of thousands of gallons annually.

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