Adaptive benefits of daylight availability and the photoperiodism of transhemispheric migrants

University Of North Carolina At Chapel Hill, Chapel Hill NC

Investigators

Abstract

Many birds use daylength (availability of daylight) to synchronize annual reproduction with appropriate habitat conditions and with others, such as mates. Migratory birds modify their exposure to daylight due to the effects of latitude on daylength. This study examines whether birds that migrate to the southern hemisphere use cues from the earth's magnetic field to change their sensitivity to daylight so that breeding occurs in only one hemisphere. It also examines whether the longer summer days of high latitudes facilitate parental provisioning of baby birds compared to the shorter summer days of low latitudes. This will aid in the understanding of the ecological and physiological bases for long-distance migration. Because daylength is an astronomical phenomenon, the P.I. will partner with a public science center in the construction of exhibits to teach school children about the astronomy of daylength and about migratory birds. The P.I. will also partner with First Nations and Métis people of northern Canada to ensure that field work in this region is sensitive to cultural and environmental issues and to learn traditional knowledge as it pertains to high-latitude wild animals. The research will expand knowledge in a fundamental biological response to global change, migration to high latitudes. It is highly interdisciplinary, being biological, geographical, and astronomical in nature. But it further addresses issues important to the conservation of animals that reside in some of the world's most endangered ecosystems, those of high latitude that are particularly susceptible to global change. In moving between photoperiodic schedules of different latitudes, individual latitudinal migrants modify the number of hours of daylight per year to which they are exposed. Whether or not daylight availability associated with migration has direct fitness benefits, such as enabling more time each day to feed rapidly growing young, has never been examined. Also, the type of latitudinal migration that is trans-equatorial cannot be reconciled with current knowledge on avian photoperiodism, which regulates the seasonal timing of breeding and other life-history transitions. This proposal aims to determine if the additional summer daylight availability at higher latitudes accelerates parental provisioning and thus offspring growth relative to lower latitudes and to identify a photoperiodic and geomagnetic mechanism that enables unihemispheric breeding under transhemispheric migration. It will examine nestling growth in both free-ranging Lincoln's sparrows along a transect from central New Mexico to over 60° latitude and in laboratory zebra finches under experimentally manipulated photoperiods and food availability. It will also use photoperiod and geomagnetic manipulations in laboratory-housed bobolinks, a transequatorial migrant that breeds in the northern hemisphere but overwinters in the southern hemisphere, to examine the physiological mechanisms regulating breeding in a transequatorial migrant. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.