Risk of migration: not all gregarious locust nymphs reach appropriate refuges

Area of Science:

• Ecology
• Animal Behavior
• Evolutionary Biology

Background:

• Ectotherms rely on refuges for predator defense, especially in cold, due to limited active evasion.
• Migratory species may face challenges in selecting optimal refuges, impacting survival.
• Desert locust nymphs (Schistocerca gregaria) experience daily thermal constraints in the Sahara Desert.

Purpose of the Study:

• To investigate how migratory ectotherms modify defensive behaviors in response to refuge quality during cold periods.
• To determine the influence of roosting plant type and height on desert locust nymph defense strategies.

Main Methods:

• Observational study of gregarious desert locust nymphs in the Sahara Desert.
• Simulated ground predator approach to elicit defensive behaviors.
• Recorded roosting plant type (bush/shrub) and height (e.g., >2 m, <1.5 m).
• Documented two primary defense behaviors: dropping and remaining stationary.

Main Results:

• Locusts in bushes typically dropped and hid, regardless of bush height.
• Nymphs roosting on shrubs >2 m high remained stationary.
• On shrubs <1.5 m high (insecure refuges), nearly half exhibited both dropping and stationary behaviors, indicating indecision.
• Defensive behaviors were effective and matched refuge types, minimizing the need for locomotion.

Conclusions:

• Desert locust nymphs exhibit flexible anti-predator behaviors contingent on refuge availability and quality.
• Selecting appropriate refuges before daily thermal limitations is crucial for migratory ectotherm survival.
• Migration poses risks for ectotherms due to potential challenges in timely refuge selection.