Androgen Regulation of Avian Premigratory Hyperphagia and Fattening: From Eco-Physiology to Neuroendocrinology

In many high latitude-breeding avian species, reproductive andwintering seasons are separated by migratory periods that involvedramatic physiological and behavioral adjustments such as hyperphagiaand fat deposition. The endocrine mechanisms responsible forthese adjustments have been extensively studied, yet remainonly partly understood. The currently available informationindicates that food consumption and/or fattening can be experimentallymodulated by multiple hormones including testosterone, prolactin,glucocorticoids, and opioids. These hormones may control migratoryfunctions through mutual interactions rather than independently.Little is known, however, concerning the nature of these interactionsand their relative importance in the control of annual cyclesin natural conditions. This paper focuses on the role of gonadalandrogens in the control of migratory functions, and it summarizesthe information which is available on the physiological andbehavioral interactions between these androgens and other hormones.     

Endocrine Bases of Spatial and Temporal Opportunism in Arctic-Breeding Birds

The primary objectives of this paper are to define, explorethe environmental factors favoring, and discuss hypotheses concerningthe endocrine bases of two important arctic breeding strategiesthat we call spatial and temporal opportunism. We identify severalspecies that display spatial opportunism in the Arctic, andone that displays temporal opportunism. In spatial opportunism,breeding may be highly seasonal but the locality where individualsbreed may change from year to year as a result of unpredictablespatial distribution of food, nest site availability, or otherfactors such as predator abundance. We suggest that flexibilityof the transition from migration to settlement distinguishesspatial opportunists from site-faithful migrants. Thus far,data are available for only two hypotheses regarding the endocrinebasis of this flexibility. Circulating patterns of testosterone(associated with territory establishment) and corticosterone(associated with migratory activity) appear not to be involvedin the regulation of spatial opportunism in white-crowned sparrows(Zonotrichia leucophrys gambelii), but more detailed study isnecessary. In temporal opportunism (that may occur simultaneouslywith spatial opportunism), temporally variable food availabilityapparently selects for the capacity to initiate reproductionacross a wide portion of the year. Tonic activity of the hypothalamo-pituitary-gonad(HPG) axis could provide a mechanism to minimize the delay betweendiscovery of abundant food and onset of nesting in any season.However, the evidence for one arctic temporal opportunist, thewhite-winged crossbill (Loxia leucoptera), indicates that theHPG axis is not tonically active, but probably switches off(i.e., becomes photorefractory) in autumn, as for other birdsbreeding at these latitudes. Opportunistic breeding very earlyin the year (e.g., March near Fairbanks, Alaska) is associatedwith increased luteinizing hormone secretion, probably in responseto a combination of abundant food and social stimuli, afterrefractoriness dissipates. We have taken the first step of identifyingspatial and temporal opportunism as important phenomena in theArctic, and discussing hypotheses related to endocrine mechanisms.Future research should identify specific environmental cuesinvolved, and elucidate the neuroendocrine and endocrine mechanismsunderlying these two reproductive strategies.     

Short-term Modulation of Domestic Pigeon (Columbia livia L.) Behaviour Induced by Intraventricular Administration of ACTH

The behavioural responses induced in adult domestic pigeons by intraventricular injections of 0 to 6 IU of ACTH 1–39 are reported. The frequency of 10 different behaviour patterns was recorded for 90 min after administration of the peptide. The effect that was induced was complex, the frequency of some patterns increasing (yawning, headshaking, body shaking, wing-flapping), of some others decreasing (feeding, one-wing stretching, eye closing) or remaining unchanged (preening). The frequency of several patterns was maximal during the first 30 min following the injections but this was shown in some cases to be independent on the hormone administration.