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Table 1 Summary of tested hypotheses on the evolution of growth patterns in passerine birds

From: Adaptation and constraint shape the evolution of growth patterns in passerine birds across the globe

Factor Reasoning Predictions for growth rates Predictions for trait development at fledging and fledging age
Time-dependent mortality
 Nest predation High risk of nest depredation selects for fast growth and early fledging. Faster growth rate under high nest predation. Growth rate of wings might be especially prioritized to enable escaping from predators. Early fledging, potentially with less developed locomotor traits, under high nest predation.
Energy
 No of caregivers Higher energy availability enables fast growth and better trait development. Growth rate faster with more care-givers (Cooperative breeding > pairs > female-only care). Early fledging and/or better development of locomotor traits with more care-givers.
 Clutch size Energy requirements increase with both chick number and growth rate. Slower growth in large broods due to energetic constraint. Delayed fledging or less developed locomotor traits in large broods.
Constraint/Opportunity
 Nest height Ground nesting enables early fledging and thus escaping whole-brood depredation (for a given nest predation rate). Fast growth in ground-nesters; slower growth in species nesting higher up. Less developed locomotor traits in ground-nesters; better trait development and delayed fledging in species nesting higher up.
 Foraging substrate Ground foraging enables early fledging and thus exploitation of resources by parents; vegetation and air foraging requires high-quality locomotor traits, esp. wings. Fast growth in ground-foragers; slower growth in species foraging on vegetation and especially in the air (wings). Less developed locomotor traits in ground-foragers; better trait development and delayed fledging in species foraging on vegetation and especially in the air (wings).
Geography
 Latitude Tropical species have overall slow life history and invest into fewer, higher-quality young. Slow growth in tropical species. Better developed locomotor traits and delayed fledging in tropical species.