Summer diet of king penguins (Aptenodytes patagonicus) at the Falkland Islands, southern Atlantic Ocean

The diet of king penguins (Aptenodytes patagonicus) brooding chicks was investigated during February 2001 at the Falkland Islands, where a small but increasing population is located at the limit of the breeding range of this species. Fish was the most important food source by number (98.0%) and reconstituted mass (97.8%), squids accounting for the remainder. Myctophid fishes represented the main part of the diet (97.7% by number and 96.6% by reconstituted mass), Protomyctophum choriodon being by far the main prey item (84.2% and 88.1%, respectively). Four other myctophids and one squid species each contributed to more than 1% of the diet by number: Krefftichthys anderssoni (4.8%), Electrona carlsbergi (4.6%), Gymnoscopelus nicholsi (2.2%) and Protomyctophum tenisoni (1.8%), together with small juveniles of Gonatus antarcticus (1.8%). Twelve squid species were identified from accumulated lower beaks, including the ommastrephid Martialia hyadesi (48.3% by number), the onychoteuthids Moroteuthis ingens (15.6%), Kondakovia longimana (10.5%) and Moroteuthis knipovitchi (7.3%), and Gonatus antarcticus (9.2%). The stable-carbon and stable-nitrogen isotopic composition of chick food and adult blood differed in a way that suggests that, during the same trip, adult birds fed for themselves in distant foraging grounds, and fed for their chicks on their way back to the colony. The study emphasizes that king penguins are specialist myctophid eaters throughout their breeding range in summer, and highlights the importance of Protomyctophum choriodon as a link between zooplankton and top predators in the pelagic ecosystem of the southwestern Atlantic Ocean.     

Failure to implicate cAMP in transduction in lobster olfactory receptor cells

The possible role of adenosine 3',5'-cyclic monophosphate (cAMP)in olfactory transduction in the spiny lobster was investigatedusing radioimmunoassay of cAMP and intracellular recording.Application of forskolin or 1-isobutyl-3-methylxanthine increasedcAMP levels in intact sensilla containing the chemoreceptiveouter dendritic segments of the lobster olfactory receptor cell,thereby demonstrating adenylate cyclase and phosphodiesteraseactivity in the sensilla. A complex odor mixture and identifiedexcitatory odor molecules failed to stimulate the productionof cAMP, however In intracellular recordings, superfusion ofthe outer dendritic segments with forskolin, 1-isobutyl-3-methylxanthineand cyclic nucleotide analogs had no direct effect on odor-responsivecells. These compounds did cause infrequent enhancements (sixof 42 cells) of odor-evoked receptor potentials, but processesother than transduction are the most likely causes of this effect.We conclude that cAMP-dependent transduction mechanisms areunlikely to mediate most odor responses in lobsters, in contrastto transduction mechanisms in amphibians and rats.     

Sex Steroid–Opioid Interactions Associated with the Temporal Component of Avian Calling Patterns

Isolation from conspecifics in young, precocial birds predictably induces distress vocalizations (DV) and androgens change this type of vocalization into male typical “crowing” (CR). In addition, opioid peptides are known to exert potent effects on avian vocal behavior. Here we investigate the organizational and activational correlates of sex-steroid actions on opioid-receptor organization and their relevance to the temporal evolution of DV and CR. From the effects of pre- and postnatal steroid applications and postnatal [³H]etorphin binding studies, we find that early steroidal effects become manifested at the behavioral level by changing the characteristic duration of vocalizations. In the male quail this extension of calling duration is accompanied by a clear decrease in opiate binding, whereas in the female there is a moderate increase in binding sites. The transition from DV to CR (within hours) induced by testosterone is correlated with “upregulation” of opiate receptor sites within unilateral brainstem areas of young male quail. Based on these findings, we suggest that organizational steroid effects change the characteristic duration of isolation-induced vocalizations and these effects appear to be manifested at the level of opioid-receptor distribution.     

A simple and low‐cost method to estimate spatial positions of shorebirds: the Telescope‐Mounted Angulator

ABSTRACT Estimating the spatial position of birds in open habitats like intertidal mudflats is important for many studies, for example, detailed density estimates or linking predation pressure to resource availability. To date, several methods have been used to estimate the positions of birds, including density counts in predetermined plots, range finders, photography, and tracking individuals tagged with GPS‐equipped transmitters, and each method has advantages and shortcomings. Counts in premarked plots are possible over relatively long distances, but small‐scale information is lost due to within‐plot averaging. Other methods accurately determine the position of individuals, but can only be used at relatively short distances or involve capturing birds. We describe a simple and low‐cost method to estimate the spatial position of individual birds in open habitats using a telescope‐mounted instrument that measures the scope's viewing angle. Using this Telescope‐Mounted Angulator (TMA), the distance to focal birds can be calculated by simple trigonometry, requiring only the viewing angle and mounting height of the telescope. Laboratory tests revealed that the TMA was most accurate when calibrated for individual observers. Field experiments performed on a 4‐m high observation platform showed that the TMA can estimate the position of shorebirds with an accuracy of 18 to 36 m up to a distance of 500 m. By also including the direction, determined with a compass, the spatial position of birds can be reliably estimated. The TMA can be a valuable tool for estimating the spatial position of animals in various flat landscapes, providing detailed measurements in a relatively short period of time.