ornithology 3/20
Molting and Breeding Cycles in Birds
Nesting and Molting
As birds finish nesting, they begin to molt.
Molting usually starts in March, with some chicks continuing until September.
Molting occurs primarily after breeding.
Breeding and Molting Relation
Birds generally do not molt while breeding; they wait until breeding is complete.
Early molting birds are those that have stopped breeding.
Annual Cycles of Temperate Birds
Birds in temperate regions cannot perform all life history events simultaneously as each demands resources and energy.
Migratory and non-migratory birds exhibit similar molting behaviors—molting occurs post-breeding.
Behavioral Patterns in Late Summer
Migratory birds often flock in late summer, aiding in protection from predators and food accessibility.
At the end of summer and early fall, food resources are typically abundant, supporting molting and migration.
Hormonal Changes and Migration
Spring migration (or vernal migration) in birds is triggered by hormonal changes primarily influenced by environmental cues, especially photoperiod.
Other cues can include temperature and weather conditions.
Post-Molting Behavior
After completing molting, decreased photoperiods trigger birds to prepare for migration to wintering areas, focusing on survival strategies.
Resident Bird Populations
In milder climates, some birds bypass migration and adapt their behaviors to ensure survival over winter, preparing for breeding as the photoperiod increases in spring.
Data Representation of Bird Movements
eBird data illustrates the movements of 18 bird species across dates, showing fall migration patterns and wintering areas.
Impact of Weather on Migration
Sudden cold spells during fall can affect food availability, influencing migration decisions.
Birds pay attention to the weather; short-distance migrants may react to both photoperiod and food availability as cues for movement.
Influence of Prey Availability
An increase in available prey can deter migration, while a decrease may prompt movement to better locations, although such changes do not indicate destination effectively.
Fitness and Reproductive Success
Concepts of fitness enhancement are discussed, particularly related to increased food availability allowing birds to rear more offspring (e.g., feeding more babies with longer daylight).
Understanding of Migration Triggers
Distinction between seasonal migration and immediate responses (like reacting to weather conditions) is important. Seasonal migration is driven by the right cues to prepare for breeding grounds.
Circadian vs. Circannual Rhythms
Circadian rhythms refer to the 24-hour biological cycles, while circannual rhythms represent yearly cycles, both critical in understanding avian behavior.