Animal migration Study Guide

📖 Core Concepts Animal migration – regular, seasonal or annual long‑distance movement tied to a life‑cycle event (e.g., breeding, feeding). Obligate vs. facultative – obligate migrants must move each season; facultative migrants may stay if conditions are favorable. Complete / partial / differential migration – all individuals move, only some move, or movement varies with age/sex. Primary drivers – climate change, food availability, reproductive needs, over‑population or famine (irruptive). Types of migration Circadian – timed by daily/annual biological clocks. Tidal – timed to rising and falling tides. Diel (daily) – vertical or horizontal movement within a 24‑h period. Navigation strategies – sun compass (adjusts for sun position) + magnetic sense (detects Earth’s field). Classification of fish migrations Diadromous – any life‑stage shift between fresh and salt water. Anadromous – born in fresh water → ocean → return to fresh water to spawn (e.g., salmon). Scale – migrations can span thousands of kilometres (e.g., Arctic tern ≈ 19,000 km round‑trip). Timing cue – photoperiod (day length) triggers hormonal cascades that ready the animal for travel. Taxonomic examples – birds (≈ 1,800 migratory species), fish (≈ 120 diadromous species), insects (monarchs, locusts), mammals (long‑distance bats), reptiles/amphibians (sea turtles, breeding frogs). Study methods – bird rings, radio‑tracking collars, lightweight tags for tiny species. 📌 Must Remember Migration requires regularity and a seasonal/annual pattern – irregular dispersal ≠ migration. Obligate = must migrate; facultative = may skip migration. Complete = whole population migrates; partial = only a subset; differential = variation by age/sex. Photoperiod → hormone change → physiological prep → departure is the classic trigger chain. Arctic tern holds the distance record: ≥ 19,000 km per year. ≈ 1,800 of 10,000 bird species migrate long distances. ≈ 120 fish species are diadromous; many are anadromous (e.g., salmon). Sun compass and magnetic sense are the two main avian orientation tools. Tracking choice depends on animal size: rings → large birds; radio collars → medium mammals/birds; miniature tags → small birds/insects. 🔄 Key Processes Photoperiod detection Day length sensed → hypothalamus interprets change. Hormonal cascade Increased melatonin & gonadotropins → body‑fat accumulation, muscle remodeling. Physiological preparation Fat storage, feather/scale molt, muscle hypertrophy. Departure Navigation system activated (sun compass → magnetic map). Navigation during flight Continuously adjust sun‑compass angle; use magnetic field for correction. 🔍 Key Comparisons Migration vs. Dispersal – Migration is regular, seasonal; dispersal is irregular, non‑seasonal. Obligate vs. Facultative – Obligates always move; facultatives can stay if conditions permit. Complete vs. Partial vs. Differential – All vs. some vs. variation by age/sex. Anadromous vs. Diadromous – Anadromous: fresh → salt → fresh (spawning). Diadromous: any fresh–salt shift (includes anadromous & catadromous). Circadian vs. Tidal vs. Diel – Daily/annual clock vs. tide‑linked vs. 24‑h vertical/horizontal shifts. ⚠️ Common Misunderstandings “All long‑distance movements are migrations.” – Irregular irruptions are not true migration. “Only birds migrate.” – Many fish, insects, mammals, reptiles, and amphibians also migrate. “Magnetic sense is the only compass.” – Birds combine sun compass with magnetic cues. “All fish migrations are anadromous.” – Many are diadromous without the fresh‑water‑to‑spawning pattern. 🧠 Mental Models / Intuition Seasonal commute – Think of migration as a yearly work commute driven by a “clock” (photoperiod) and “paycheck” (food/reproduction). Dual GPS – Birds use a sun‑based map (daytime) and a magnetic map (all times) like having two GPS systems for redundancy. Push‑pull – Environmental “push” (cold, scarce food) plus “pull” (breeding habitat, abundant food) determines direction. 🚩 Exceptions & Edge Cases Facultative migration – Some populations may skip migration during mild winters. Partial migration – Only certain age classes (e.g., juveniles) migrate. Irruptive movements – Triggered by famine or overpopulation; irregular and not seasonal. Multi‑generational insect migrations – Monarchs complete the full route over several generations. 📍 When to Use Which Identify migration type → If movement aligns with tides → label tidal migration. Choose classification → Freshwater → ocean → freshwater = anadromous; any fresh‑salt shift = diadromous. Select tracking method → Large birds/ mammals → ring/tag or radio collar. Small birds/insects → lightweight telemetry or nanotags. Determine cue focus → If study emphasizes timing → measure photoperiod and hormone levels. 👀 Patterns to Recognize Photoperiod change → hormone surge appears in most bird migration questions. Long‑distance marine‑freshwater transitions signal diadromous fish. Multi‑generation stages hint at insect migrations (e.g., monarch). Vertical diel movement often linked to predator avoidance or feeding (e.g., zooplankton). 🗂️ Exam Traps Distractor: “Migration only occurs in warm‑blooded animals.” – False; cold‑blooded fish, reptiles, amphibians also migrate. Distractor: “All fish that move between fresh and salt water are anadromous.” – Incorrect; many are diadromous but not anadromous. Distractor: “Photoperiod is irrelevant for mammals.” – Misleading; many migratory mammals also respond to day‑length cues. Distractor: “Tidal migration is exclusive to marine mammals.” – Wrong; many fish and invertebrates use tides. Distractor: “Bird rings provide real‑time location data.” – Rings only give presence when recovered; not continuous tracking. --- Use this guide for rapid recall before the exam – focus on the bolded keywords and the cause‑effect chains!