Life-history theory predicts that animals will only pay the costs of a risky return journey when the expected reproductive payoff justifies it. In a field study of the mound-building brush turkey, researchers surgically fitted incubating females with tracking tags before relocating them at varying distances from their mounds, then recorded which birds successfully returned. Return success declined sharply as relocation distance grew, and the initial explanation offered was that birds released beyond a certain radius simply lost track of their mound's location entirely. That explanation runs into difficulty, however, once the full dataset is examined: even at the farthest release point used in the study, a handful of birds nonetheless made it back, which points to a motivational rather than a purely navigational limit. A more persuasive account rests on the balance between exertion and reward. Flight in this species carries a substantial metabolic price, and monitor lizards patrolling the forest floor pose an ever-present threat to unattended mound contents; the longer a female spends away, the more that threat compounds. In one striking case, a bird required nine full days to make her way back after being released 4 kilometers from her mound—well beyond the window in which a resident monitor lizard would typically have discovered and excavated the eggs. Even so, females tending unusually large mounds, representing a bigger reproductive investment, returned at markedly higher rates from distances exceeding 800 meters than females with modest mounds released the same distance away, suggesting that when the stakes were high enough, the payoff justified absorbing costs that would otherwise deter a return trip.

1. The primary purpose of the passage is to

A. cast doubt on the methodology used to study homing behavior in brush turkeys
B. weigh competing explanations for a pattern observed in brush turkeys
C. explain why mound size varies among individual brush turkeys
D. establish that monitor lizards are the principal threat to brush turkey eggs
E. argue that reproductive investment determines all aspects of parental behavior in brush turkeys


2. The highlighted sentence relies on which of the following assumptions about the birds that returned from the farthest release point?

A. They faced a lower risk of detection by monitor lizards than did the other birds released at that distance.
B. They were guarding smaller mounds than were the other birds released at that distance.
C. They had not simply been released at a point closer to their mounds than researchers intended.
D. They did not possess a categorically different, superior capacity to navigate back to their mounds than the birds that failed to return.
E. They expended less metabolic energy in flight than did the birds that failed to return.


3. The "more persuasive account" suggests which of the following as a possible explanation for female brush turkeys that failed to return from distances beyond 800 meters?

A. They were tending mounds of below-average size.
B. They had lost the ability to locate their mounds at that distance.
C. They were physically incapable of completing a flight of that length.
D. Their mounds had already been claimed by rival females.
E. They had sustained tag-related injuries during the relocation procedure.