Methods of entrainment to food and survival advantages

• Because of weak zeitgeber of light (during winter and summer months where there is very little change in photoperiod, while in autumn, photoperiod decreases rapidly) and only periodic access to food during winter months, it is advantageous for birds to be more strongly entrained to food as a zeitgeber to anticipate its availability
• Having food as the main zeitgeber also means a longer feeding period in autumn (when day length is rapidly decreasing) than if controlled by light. This enables better fat stores before winter.
• In spring the birds may stock up on food to facilitate successful reproduction before competitors (other non-resident birds) arrive back.