Migration Definition – twice annual movement between a restricted breeding/wintering area and a restricted winter/breeding area: a two-way trip.
Did you know... ...that the longest annual bird migration is made by the Arctic Tern? The round trip distance from it's northern summer home in the Alaskan Arctic to its southern territory in the Antarctic can be up to 18,000 miles! Arctic Tern
On the other end of the spectrum…Clark's Nutcracker flies only a few miles to move from its home high in the Rocky Mountains or Sierras to lower spots in the same mountain ranges.
Upon arrival at southern wintering grounds birds have been described as nothing more than “feathered skeletons” having depleted their fat reserves and much of their protein. Up to 12 million birds have passed over Cape Cod in one night, embarking on a non-stop journey of 80 to 90 hours. Radar stations on Bermuda and Antigua pick up the approaching waves of migrants.
Controlling Factors and Control Mechanisms of Migration • 1. Sources of Information • Proximate factors – “provide actual timing that brings adaptation into play…those that twice annually bring the migratory bird into actual migration…annual stimulus for migration • Ultimate factors – “give a survival value to the adaptation of the birds cycle to that of the environment… have made the migratory pattern useful to a species
Controlling Factors and Control Mechanisms of Migration • 2. Climate, Weather, Food – as proximate factors • -Known as early as 13th century that birds “follow food supply and heat” • -Detailed analysis has shown that other factors may have specific effects to some bird species, including temperature, moisture, pressure, atmospheric humidity, cloudiness, wind direction and velocity, seed time of plants, etc. • -Experiments in lab – can induce migratory restlessness by manipulating temperature, photoperiod, and air pressure.
Controlling Factors and Control Mechanisms of Migration • 3. Photoperiod – most precise way to predict environmental changes. • -Rowan, W. 1925. Relation of light to bird migration and developmental changes. Nature 115:494-495 • -Artificially increased day length in winter; caused migratory behavior, hyperphagia, body weight increase, and fat deposition in Slate-colored Juncos and Common Crows • - O.K. for fall departures from North America, but what about spring departures from Central and South America
Components of Control System • A. Hypothalamus, pituitary gland, pineal gland • Hypothalamus– prolactin releasing factor (PRF) stimulates prolactin production which induces restlessness and fat deposition. Appears to be the translator of photoperiod effects, …perhaps an internal clock? • Pituitary Gland– secretes prolactin
Components of Control System • B. Gonads • Early belief that gonadal hormones stimulated migratory behavior, yet castrates still showed migratory behavior • Restlessness occurs before gonadal development in the spring for most species, thus most available evidence suggests that gonads and sex hormones do not play a primary role in bird migration
Seasonal cycles of climate or insect abundance attract corresponding cycles of breeding, flocking, and migratory relocation • Migration benefits are species or population specific and include the need to escape inhospitable climates, probable starvation, social dominance, shortage of nest/roost sites, or competition for food • A more positive view of the same ecological forces is that migrants aggressively exploit temporarily available opportunities
Metabolic Physiology of Migration • Fat deposition – hyperlipogenesis and fat deposition now documented in > 40 families • Comparable fat deposition does not occur in resident species, races, and populations…or does it?? • Amounts of Fat – Gambel’s White-crowned Sparrow 35-50% of total carcass lipid is adipose tissue, most is stored in distinct “fat organs”, the remainder is tied up in tissues
Total amount of body fat varies according to species and distance to be traveled
Eugene Odum used the amount of body fat present in birds collected at a series of T.V. towers along the coast of Florida to predict how far they could travel non-stop. Used a migratory metabolic rate of 2.25 times existence energy. Found the following; White-throated sparrows - 75 milesIndigo Buntings (thin) - 169Indigo Buntings (fat) - 465Red-eyed Vireo (thin) - 190Red-eyed Vireo (fat) - 710 Red-eyed Vireo (fatter) - 1070Parulidae (Warblers) - 632Summer Tanager - 1170Scarlet Tanager - 1278Bobolink - 1237
Orientation & Navigation It has been demonstrated that birds rely on several different cues – visual landmarks, geomagnetic field, solar compass, skylight polarization pattern/stars, and olfaction - for their orientation and navigation across vast stretches of land
Of course some crashed into the loft and some missed the loft altogether. Research on bird Navigation and Orientation • Schlicte and Schmidt-Koenig (1971) fitted well trained homing pigeons with frosted contact lenses that limited image formation beyond 3 meters. The blind birds flew over 170 km directly back to their lofts.
-On cloudy days the penguins wandered about randomly. • Emlen and Penny (1964) took Adelie Penguins from their coastal breeding rookeries to interior Antarctica and released them. -However, when the sun was shining they headed north-northeast towards the coast, compensating for the sun’s counterclockwise movement in the southern hemisphere by correcting their orientation 15 degrees per hour clockwise relative to the sun’s position…. …By the way the sun changes continuously by 15 degrees per hour.
Research on bird Navigation and Orientation • Franz and Eleanore Sauer (1957) demonstrated the use of stars for navigation by birds. By caging Garden Warblers in a Planetarium, the Sauers showed birds oriented north in the “spring” and south in the “fall” under simulated night skies. • -When they turned off the stars the birds became disoriented. • -When they rotated the north-south axis of the planetarium 180o the warblers also reversed their compass headings.
Merkel and Wiltschko (1965) showed European Robins could orient in solid steel cages without celestial cues. They also demonstrated that the robins reversed their orientation when the magnetic field imposed on the cage was reversed. European Robin Research on bird Navigation and Orientation
-Keeton concluded that the pigeons use the sun preferentially to the earth’s magnetic field on sunny days. Research on bird Navigation and Orientation • Continuing the magnetism work Keeton (1971) demonstrated that free flying homing pigeons wearing bar magnets often did not orient properly on cloudy days vs. control pigeons wearing brass bars.
Research on bird Navigation and Orientation • Finally, Walcott and Green (1974) fitted homing pigeons with electric caps that produced a magnetic field through the birds head. • -Under overcast skies, reversing the field’s direction by reversing the current in the cap caused free-flying pigeons to fly in the direction opposite their original course. Question of the day:What would you do if someone switched the electromagnetic field in your brain by pumping an electrical current into it?
Web Links Bird Migration Ecologyhttp://orn-lab.ekol.lu.se/birdmigration/ Bird Migration Factshttp://north.audubon.org/facts.html More on Flywayshttp://www.birdnature.com/flyways.html