When the sun never sets: diverse activity rhythms under continuous daylight in free-living arctic-breeding birds.

Circadian clocks are centrally involved in the regulation of daily behavioural and physiological processes. These clocks are synchronized to the 24 h day by external cues (Zeitgeber), the most important of which is the light-dark cycle. In polar environments, however, the strength of the Zeitgeber is greatly reduced around the summer and winter solstices (continuous daylight or continuous darkness).

Evidence for adaptive evolution of olfactory receptor genes in 9 bird species.

It has been suggested that positive selection, in particular selection favoring a change in the protein sequence, plays a role in the evolution of olfactory receptor (OR) gene repertoires in fish and mammals. ORs are 7-transmembrane domain (TM) proteins, members of the G-protein-coupled receptor superfamily in vertebrate genomes, and responsible for odorant binding and discrimination. OR gene repertoires in birds are surprisingly large and diverse, suggesting that birds have a keen olfactory sense.

A comparison of reptilian and avian olfactory receptor gene repertoires: species-specific expansion of group gamma genes in birds.

Background: The detection of odorants is mediated by olfactory receptors (ORs). ORs are G-protein coupled receptors that form a remarkably large protein superfamily in vertebrate genomes. We used data that became available through recent sequencing efforts of reptilian and avian genomes to identify the complete OR gene repertoires in a lizard, the green anole (Anolis carolinensis), and in two birds, the chicken (Gallus gallus) and the zebra finch (Taeniopygia guttata).

Low metabolism and inactive lifestyle of a tropical rain forest bird investigated via heart-rate telemetry.

Birds in the lowland tropical rain forest are expected to have low energy turnover. Here, we used heart rate telemetry to estimate nighttime resting metabolic rate (RMR), daily energy expenditure (DEE), and locomotor activity of a small, long-lived tropical rain forest-understory bird, the spotted antbird (Hylophylax naevioides). Heart rate was linearly related to oxygen consumption in respirometry measurements that encompassed 96% of heart rates measured in wild birds.

Evidence for increased olfactory receptor gene repertoire size in two nocturnal bird species with well-developed olfactory ability.

Background: In vertebrates, the molecular basis of the sense of smell is encoded by members of a large gene family, namely olfactory receptor (OR) genes. Both the total number of OR genes and the proportion of intact OR genes in a genome may indicate the importance of the sense of smell for an animal. There is behavioral, physiological, and anatomical evidence that some bird species, in particular nocturnal birds, have a well developed sense of smell.

Avian olfactory receptor gene repertoires: evidence for a well-developed sense of smell in birds?

Among vertebrates, the sense of smell is mediated by olfactory receptors (ORs) expressed in sensory neurons within the olfactory epithelium. Comparative genomic studies suggest that the olfactory acuity of mammalian species correlates positively with both the total number and the proportion of functional OR genes encoded in their genomes. In contrast to mammals, avian olfaction is poorly understood, with birds widely regarded as relying primarily on visual and auditory inputs.

Detection of olfactory receptor transcripts in bird testes.

The sense of smell is mediated through olfactory receptors (ORs) expressed in olfactory sensory neurons of the olfactory epithelium. Interestingly, some OR genes also function in another context: they are expressed in nonolfactory testicular tissue and in sperm of mammals and fish where they mediate sperm flagellar motility. The presence of OR transcripts in testicular tissue of both mammals and fish suggests that this is a conserved trait among vertebrates.

Plasma steroid hormones in two Arctic-breeding shorebirds: monogamy versus polygyny.

Steroid hormones are predicted to vary with mating systems, degree of paternal care and aggression, as proposed in the "challenge hypothesis." We measured plasma concentrations of testosterone (T) and 5alpha-dihydrotestosterone (DHT) in two high Arctic breeding and closely related shorebird species, the polygynous pectoral sandpiper (Calidris melanotos) and the monogamous semipalmated sandpiper (Calidris pusilla) to examine whether the hormonal findings corroborate the predictions of the challenge hypothesis. In both species, males showed significantly higher levels of DHT and T than females, but in pectoral sandpipers median T levels were 34 times greater in males than in females, whereas in semipalmated sandpiper there was only a 4.