Resident vs. Migrant Birds: Who copes better with change?
Environmental changes occur continuously. Seasons change. Food sources disappear. Forested land is cleared for houses or agriculture. How birds react to these environmental changes can give them an evolutionary advantage.
To deal with change, birds can either migrate to another location (migrant birds) or stay and develop new ways to adapt to the change (resident birds).
To survive, birds constantly collect information about their surroundings. But the amount of information collected depends upon whether the bird is a migrant or a resident.
It makes sense for resident birds to collect more information about their environment than migrants, since the residents will use that information to discover and take advantage of new resources and make decisions about long-term habitat suitability.
Migrants, on the other hand, are repeatedly confronted with unfamiliar environments in which they must quickly discover food and identify predators. They are only in an area for a short time. Once migrants move on, the information is no longer as useful.
Scientists have observed birds exhibiting two distinct types of behavior when presented with changes in their environment: neophilia, or attraction to new things, and neophobia, the fear of new things. These are two independent, behavioral reactions that occur at the same time, but by varying degrees.
In a study by Claudia Mettke-Hofmann of the Smithsonian Migratory Bird Center, resident Sardinian warblers were observed approaching and spending more time near a new object near a feeding dish than migratory garden warblers.
The resident warblers approached the food dish with much less hesitation than the migratory warblers. Since resident birds are constantly seeking new resources in a limited area with an environment that changes year-round, this makes sense. Less fear of new things allows residents to find new kinds of food and even develop new feeding techniques.
On the other hand, since migrants are not restricted to a certain area, the cost of missing out on a new food source may be outweighed by the benefit of avoiding a predator. They can avoid dangerous situations by exhibiting neophobic behavior to new things in their environment. They simply move on to another area and another food source if needed.
As a result, migrants are more motivated to enter a new, unfamiliar environment, or they have high spatial neophilia. This trait was exhibited in another study by Mettke-Hofmann. The study found migrant garden warblers were less hesitant to enter and explore a new room than resident Sardinian warblers.
For migrants, this high spatial neophilia to approach and enter an area speeds up migration and attracts the birds to suitable stopover sites. Residents, on the other hand, rarely have the need to explore new areas and can be very cautious about doing so.
However, once resident birds do enter new territory, they explore it thoroughly. Migrants will often explore a site superficially or join existing flocks to locate suitable resources in a new area. This behavior allows migrants to find food faster than residents, but the resident birds aren't just looking for food. Resident birds are often collecting detailed information to use in long-term settlement decisions.
Neophilic and neophobic behavior certainly impacts what kind of information each type of bird collects, but the differences don't end there. There are also differences in the types of memories each bird retains. Migrants have long-lasting memories of good places to stop during migration and the location of the best breeding grounds. They aren't concentrating on the details of each area, so much as the overall picture.
Residents aren't collecting this kind of locality information. Instead, they are focused on remembering very detailed environmental information about changes in their limited territory. But they don't need to remember the details they are collecting for long periods of time. In fact, new, updated information on changes in their limited environment is far more valuable for their survival.
So do the different kinds of behavior and strategies for coping with environmental change give one type of bird an advantage over the other?
Based upon the neophilic and neophobic behavior observed in resident and migrant birds, migrant birds certainly seem to be at a disadvantage. Migrants' tendencies to have neophobic reactions to new objects causes them to shy away from food sources and often stay away for longer periods of time. This can also prevent them from taking advantage of new food resources.
Additionally, their long-term memory may prove to be detrimental during migration in a rapidly changing world. A suitable stopover site in the bird's memory may no longer exist because of deforestation or other man-made habitat changes, a close-by alternative may not exist.
Residents, on the other hand, are exhibiting innovation and are able to take advantage of new resources because of their neophilic behavior. They may hesitate more initially when entering new environments, but once there, they explore their new territory without much fear.
This article summarizes the information in this scientific paper:
Spatial Neophilia and Spatial Neophobia in Resident and Migratory Warblers (Sylvia). Mettke-Hofmann, C., Lorentzen, S., Schlicht, E., Schneider, J., Werner, F. 2009. Ethology, 115: 482-492.