Songbird species are showing a diversity of changes in arrival dates at their breeding and wintering grounds

Birds move seasonally between breeding and wintering grounds to take advantage of abundant resources, or to avoid predators or exposure to harsh conditions. Throughout the Northern Hemisphere, birds migrate north in the spring to nesting locations where food sources are plentiful and migrate south as temperatures drop in the fall to spend winter where environmental conditions are more favorable. As temperatures begin to warm earlier in the spring and remain warm later in the fall, birds may generally respond by shifting their migration times. Both earlier and later spring arrivals have been observed, depending on the species. For more information, download the Migratory Bird Arrivals chapter.

The Palomarin Field Station, located at the southern end of the Point Reyes National Seashore in Marin County, is the final stop for many migratory birds. It is one of the premier and longest running monitoring locations for studies on birds and their habitats.  

Credit: U.S. National Park Service

• A 36-year record of observations at the Palomarin Field Station at Point Reyes National Seashore in Marin County reveals differences in how the spring and fall arrival patterns of seven songbird species are changing.
• Of the three species studied that arrive in the spring, one is arriving early, one is arriving later, and one shows no significant change.
• Of the four fall migrant species studied, three have been arriving earlier.

Trends in spring arrival times are mixed. The Orange-crowned Warbler (left) has been arriving 2.6 days earlier per decade. The Wilson’s Warbler (middle) has been arriving 1.1 days later per decade. No significant trend was observed for the Swainson’s Thrush (right).

Credit (left to right): U.S. National Park Service, David Larson/Flickr, and Jerry McFarland/Flickr

Fall arriving birds have mostly been arriving earlier. The Golden-crowned  Sparrow (left) and the Ruby-crowned Kinglet (second to left) have been arriving earlier in the fall by 2.1 and 1.8 days per decade, respectively. The Hermit Thrush’s (second to right) arrival time has been trending earlier since 1995. The Fox Sparrow (right) shows no significant trend.

Credit (left to right):  Veit/Flickr, Shiva Shenoy/Flickr, Veit/Flickr, and Rick Leche/Flickr

• The timing of bird arrivals at breeding territories and wintering grounds is a key factor in their breeding success and survival.
• A mismatch between when birds arrive and when conditions become suitable at the arrival grounds can adversely impact bird populations. As the emergence of plants and insects in breeding grounds also change with the earlier onset of spring conditions, bird species that are unable to modify their spring arrival times may find less food, nesting materials and other resources when they arrive.
• Tracking changes in migratory bird arrivals shows how terrestrial animals may be responding to regional changes in climate. This will be important when assessing and projecting the impacts of those changes on bird populations.

• Migratory birds exhibit seasonal physiological changes in preparation for migration, triggered by environmental cues such as photoperiod (the length of day or night) and temperature. Thus, changes in the timing of spring arrivals may be in response to climatic conditions at their wintering grounds.
• As fall temperatures increase, insects and plants may be available as food for longer periods and delay fall migration.
• Migration distance, bird feeding habits, and environmental conditions at stopover locations can also affect arrival times.

• Point Blue Conservation Science, Tracking a Changing Climate