Lecture Outline. Why Study Migration? Definitions

Transcription

1 The migratory pathways above out heads are one of the world's sweetest layers he invisible arteries of feather and talon, helping knit together the planet's ecology Bill McKibben Lecture Outline Definitions Physiology & behavior Environmental cues Genetic basis for migratory behavior Definitions Migration = predictable round trip movement Partial migration = a segment of species migrants & another resident Irruptive movements = irregular seasonal occurrence of birds outside normal range Why Study Migration? Characteristic of many bird species Fascinating behavior Conservation of flyway populations Consequences of global climate change Spread of disease 1

2 Why Migrate? Proximate & Ultimate Reasons How birds migrate 1. Physiology 2. Environmental cues Why birds migrate 1. Evolutionary origins Blackpoll Warbler Why Has Migration Evolved? Costs: 1. Mortality risk 2. Lost time 3. Disorientation Benefits of moving to another region: 1. More food 2. Less predation 3. Less competition Whooping Crane Migration Studying Migration Preserved specimens Direct observation Aural Radar observation Mark & re-sight Radio telemetry Molecular data Stable isotope analysis Behavior Migratory Restlessness Zugunruhe 1. Wing-whirring 2. Duration of activity 3. Directionality Brent Geese 2

3 Migratory Behavior - Hyperphagia Changes in: 1. Behavior 2. Physiology 3. Anatomy Fuels for Migration Lipids 1. Stored sub-cutaneously 2. Acquired rapidly 3. Invertebrates, grain, etc. Protein from pectoralis major Advantages of Fat as an Energy Source Energy Yield (kj) Metabolic Water (g) Fat Migration Strategies Short hop = dunlin Long jump = bartailed godwit Carbohydrate Protein

4 Photoperiod Weather Environmental Cues Triggering Migration Orientation & Navigation 5 cues to navigate Visual landmarks Solar compass Stellar compass Geomagnetism Olfaction Experience & Map Sense Birds explore natal areas after hatch Familiarity with topography Use of Solar Compass Requires internal clock adjusting for sun s movement Unavailable for nocturnal migrants & on cloudy days 4

5 Polarized Light Vibration of electromagnetic particles 90 o angle to sun Shifts with sun s position Stellar Compass Nocturnal migrants Star patterns & rotation Learned in nest Experimentally altered 1. Planetarium-raised buntings Problems? Geomagnetic Cues Magnetite present in bird s brains Experimentally altered 1. Magnets 2. Helmholtz coils Limited evidence 1. Plugged nostrils 2. Severe or deaden olfactory nerve Short distance homing Olfactory Cues 5

6 Genetic Basis for Migratory Behavior Blackcap Warbler Nature vs. nurture Heritability Peter Berthold et al. working with Sylviid warblers 1. Juveniles Migrate Alone Wilson s phalarope Adults leave Mono Lake & arrive in S. America via great circle route Juveniles migrate along C. America Herring Gull 2. Cross-Fostering Experiments Herring gull is nonmigratory Lesser Black-backed gull is migratory Swap eggs What do offspring do? 3. Endogenous Rhythms Under constant light:dark regimes Birds maintain biorhythms Lesser Black-backed Gull 6

7 Migration Date 3. Endogenous Rhythms Zugunruhe Onset Predictable changes in behavior Even under constant light:dark regimes in captivity Strong relationship between onset in wild & captive birds Predictable Behavioral Changes Predictable timing, duration & directionality Birds exhibit enough zugunruhe to get home Pre-programmed? 4. Interspecific Differences Differences among Sylviid warblers in distance traveled Those migrating further into Africa exhibit longer periods of zugunruhe in captivity Migration Distance (Wild) Zugunruhe Duration (Captive) 5. Hybridization Experiments North to south, Blackcaps show less duration of zugunruhe Hybrid birds from parent stock at extremes of range show intermediate zugunruhe 7

8 6. Artificial Selection Blackcaps from France 76% with migratory behavior Selective breeding 30% change generation -1 How Do Juveniles Birds Successfully Migrate Alone? Innate basis to direction & duration Young explore habitats Some cues orient bird Others allow navigation Back-up system likely Cues used vary between nocturnal & diurnal migrants 8