Diet preferences as the cause of individual differences rather than the consequence

Area of Science:

• Behavioral Ecology
• Physiological Ecology
• Animal Migration

Background:

• Individual variation in animal behavior is often attributed to physiological differences.
• Emerging evidence suggests behavior, such as diet preferences, may drive physiological and morphological traits.
• Red knots (Calidris canutus islandica), molluscivorous migratory shorebirds, exhibit variation in gizzard mass and patch residence times potentially linked to diet.

Purpose of the Study:

• To investigate the causal relationship between diet preferences, gizzard mass, and patch residence times in red knots.
• To test whether individual diet preferences influence physiological traits (gizzard mass) and subsequent foraging behavior (patch residence times).

Main Methods:

• Radio-tagged 46 red knots (Calidris canutus canutus) at Banc d'Arguin, Mauritania, measuring gizzard mass.
• Utilized a novel time-of-arrival tracking system to measure patch residence times over three weeks.
• Experimentally reduced gizzard mass in 12 birds by offering soft diets and compared their residence times to controls and simulations.

Main Results:

• Patch residence times were positively correlated with gizzard mass, consistent with previous studies.
• Experimental reduction of gizzard mass did not alter patch residence times, suggesting gizzard size is not the sole determinant.
• Observed variations in patch residence times aligned with simulated values based on diet preferences.

Conclusions:

• Diet preferences appear to be a primary driver of among-individual variation in gizzard mass and patch residence times in red knots.
• Early diet experiences can have cascading effects on both behavioral and physiological trait expression.
• Understanding the ecological impact of individual differences requires considering developmental environmental influences.