SUMMARYStable isotopes of carbon are commonly used to characterize dietary preferences in animals. Because turnover rates of carbon isotopes are related to metabolic rate, we wanted to determine the rates at which carbon isotopes are exchanged in tissues of two species of nectar-feeding bats(Leptonycteris curasoae and Glossophaga soricina), both of which have relatively high mass-specific metabolic rates. To test the hypothesis that isotope turnover is higher in nectar-feeding bats, because of their high mass-specific metabolic rates, than in other eutherian mammals, we conducted diet-switching experiments and chose three target tissues (hair,wing membrane and blood) to evaluate the isotopic turnover rates. We made the following predictions: (1) isotopic composition should change towards higherδ 13C-values due to the turnover of carbon isotopes of C3 origin with those of C4/CAM origin; (2) the turnover rates of carbon isotopes would differ between the three types of tissues in the following order of decreasing turnover rates: blood>wing membrane>hair; and (3) turnover rates of nectar-feeding bats should exceed those reported for other small mammals because of the high mass-specific metabolic rate of nectar-feeding bats. Compared to the initial diet, target tissues were enriched in heavy carbon isotopes by 2.8‰ in L. curasoae and by 2.6‰ in G. soricina. After changing the diet from C3 to C4/CAM origin we found an increase in abundance of 13C in blood and wing membrane in all experimental subjects. The estimated half life of carbon isotope turnover ranged from 100 to 134 days and did not differ significantly between blood and wing membrane,nor did it differ between the two species. The low turnover rate in wing membrane may reflect its specific composition and the relatively low temperature of this tissue, and long-lived erythrocytes in bat blood may be responsible for the low turnover rate of carbon isotopes in blood. The turnover rate of stable carbon isotopes in hair was low in L. curasoae and undetectable in G. soricina, which may be explained by the seasonal growth of the hair in these two species. Because both species are small (10 and 25 g, respectively) and nectar-feeding bats have higher mass-specific metabolic rates than bats in temperate regions or similar sized terrestrial mammals, our findings of low turnover rates were unexpected.

SUMMARY We estimated the effect of nitrogen stress on the nitrogen isotope enrichments in wing membrane and blood of two nectar-feeding bats(Glossophaga soricina and Leptonycteris curasoae) by offering a nitrogen-poor diet with a high δ15N andδ 13C. Before the experiment, bats were sustained on a normal diet with a low δ15N and δ13C. Under this first food regime, the fractionation of nitrogen isotopes averaged 3.1‰δ 15N for blood and 4.4‰ δ15N for wing membrane, which was almost twice as high as the corresponding fractionation of carbon isotopes. After switching to the nitrogen-poor diet, the enrichment of heavy isotopes increased for both elements in all tissues under study. The recently published estimates of half-life of carbon isotopes indicated a low turnover rate of carbon in wing membrane and blood and an almost constant half-life over varying losses of body mass. The estimates of half-life of nitrogen were two to six times higher than those of carbon. We argue that this discrepancy was caused by the mixing of nitrogen isotopes from internal and external sources. The mixing effect was probably negligible for carbon as the amount of ingested carbon outweighed the amount of mobilized carbon from internal sources. A correlation between the estimated turnover rates of nitrogen and losses of body masses was probably obscured by the additional fractionation of nitrogen isotopes in catabolic animals. We conclude that the interpretation of nitrogen isotope data of free-ranging animals is difficult when the animal's diet is changing to a critical nitrogen content.

The hearing range of the tettigoniid Phaneroptera falcata for the echolocation calls of freely £ying mouseeared bats (Myotis myotis) was determined in the ¢eld. The hearing of the insect was monitored using hook electrode recordings from an auditory interneuron, which is as sensitive as the hearing organ for frequencies above 16 kHz. The £ight path of the bat relative to the insect's position was tracked by recording the echolocation calls with two microphone arrays, and calculating the bat's position from the arrival time di¡erences of the calls at each microphone. The hearing distances ranged from 13 to 30 m. The large variability appeared both between di¡erent insects and between di¡erent bat approaches to an individual insect. The escape time of the bushcricket, calculated from the detection distance of the insect and the instantaneous £ight speed of the bat, ranged from 1.5 to more than 4 s. The hearing ranges of bushcrickets suggest that the insect hears the approaching bat long before the bat can detect an echo from the £ying insect.

Flowering plants have evolved an extraordinary variety of signaling traits to attract their pollinators. Most flowers rely on visual and chemical signals, but some bat-pollinated plants have evolved passive acoustic floral signals. All known acoustic flower signals rely on the same principle of increased sonar reflectivity. Here we describe a novel mechanism that relies on increased absorption of the area surrounding the flower. In a bat-pollinated cactus (Espostoa frutescens) we found a hairy inflorescence zone, a so called cephalium. Flowers solely emerge out of this zone. We measured the echoes of cephalia, flowers and unspecialized column surfaces and recorded echolocation calls of approaching bats. We found that the cephalium acts as strong ultrasound absorber, attenuating the sound by -14 dB. The absorption was highest around the echolocation call frequencies of approaching bats. Our results indicate that, instead of making flowers more reflective, plants can also evolve structures to attenuate the background echo, thereby enhancing the acoustic contrast with the target.

Tympanoblissus ecuatorianus Dellapé & Minghetti, gen. et sp. nov. from the Amazon slope of the Eastern Andean Cordillera in southern Ecuador is described. This constitutes the second apterous genus known in the family Blissidae and the first with a tymbal‐like mechanism of sound production. The tiny males hide in bamboo branches where they produce a faint drumming sound. The observed vertical vibration of the abdomen and the fused first two tergites folding on both sides of the midline are consistent with the presence of a tymbal‐like organ involving the first abdominal segments. Diagnoses, descriptions and illustrations of adult males and other characters, including the genitalia, as well as oscillograms of the acoustic signal are provided.