Winter Bird Photography in the Forest and Flocking Dynamics: Part 1
As the weather begins to get colder and the days begin to get shorter in the Northern Hemisphere, many birds migrate south in search of warmer weather where food is more plentiful. Many species remain throughout the year, however, and brave the winter conditions such as the Tufted Titmouse, Baeolophus bicolor, Black-capped Chickadee, Poecile atricapillus, White-breasted Nuthatch, Sitta carolinensis, and many other species who are resident birds. Other species, such as the Golden-crowned Kinglet, Regulus satrapa, actually migrate south to the northern forests of the United States to escape the much harsher winters in the boreal forest of Canada.
Golden-crowned Kinglet pausing for a moment on an Eastern Cedar tree branch. These birds forage for small insects found hidden on the needles of conifer trees as well as on branches of deciduous trees.
During the winter months, it is common to be hiking through the forest and there is not a sound to be heard except the distant tapping of a woodpecker on a dead tree, or the creaking of trees swaying in the wind. It would appear that all the animals have left the forest, however, suddenly out of nowhere a parade of birds approach quickly, then disappear as soon as they arrived deeper in the forest.
These birds can often be found in large flocks in the winter months moving through the forest together looking for food. These flocks provide for great opportunities to create images of many different species in a small window of time. Understanding how and why these flocks operate can help you get the images that you are looking for.
These flocks can range in size from just a few individuals that are all the same species, to dozens of individuals of multiple species of birds all foraging at varying heights and methods, all trying to survive the winter. On face value, the idea of birds forming flocks to find food may seem to be counter intuitive, since there is less food in the winter and it would make sense that if more individuals were in the same area, the competition for that limited food source would make it so birds would actually eat less. While this may make sense, something actually very different occurs in these flocks that ensures that more individuals are able to survive the winter.
These flocks make the most of the idea of strength in numbers. This concept works in two ways, it works as a means of more eyes looking for food and more eyes looking for threats.
Let’s take a look at the first component, more eyes looking for food.
As more individual birds join a flock, more eyes are available for looking for food. Think of it as a giant easter egg hunt. The more people playing, the quicker it will be to find all the eggs. The food in the winter is limited and often harder to find, concealed either in the bark of trees, in dried leaves, or under the leaf litter. Many of the species that are resident birds transition from being insectivores in the breeding season, to having a broader diet in the winter months to include seeds and nuts. As more birds are foraging in a small area, the chance of any one bird detecting food is higher and even if one individual misses the food, another individual may find the food item and thus benefit. An example of this would be one individual landing on a branch for a second and ending up scaring a spider that was hiding on it. The first individual did not see the spider and flew off, causing the spider to move, becoming an easy target for a second bird to grab it. This highlights how a missed food opportunity was capitalized on because of the flocking behavior.
Black-capped Chickadee perched about 10 feet up in a tree.
There is also a social aspect to flocks. Much like a meeting of people is useful for information transfer, flocks of birds are great at transferring information. Birds work together to share information about where food is, which allows birds to find food faster if they are not familiar with the area. This has huge advantages as this spread of information reduces the movement costs of individual birds, who would have otherwise needed to spend time searching for food on their own. The metabolism of many songbirds is very fast, resulting in them burning a lot of energy moving about. A reduction in this movement to find food to make the search more efficient can mean the difference between a bird starving due to a winter storm and being able to ride the storm out on stored fat reserves.
This sharing of information is crucial for birds who are not year-round residents of the forests, such as the Golden-crowned kinglet. These birds summer in the boreal forests further north, and arrive in the forests of the Northern Unites States for Winter. These birds rely on the information they gain from joining flocks of Black-capped Chickadees and Tufted Titmouse, to find the food efficiently.
As breeding season comes to an end, many birds become less territorial, and their home ranges expand to allow for additional resources. To ensure food can be found through the home range, it is common for these flocks to move through their home range, only spending a few minutes foraging in any one area before moving on. This action ensures that no single area within their home range becomes depleted of resources.
The size and diversity of the flock is impacted by the quality of the habitat. If the habitat has a high abundance of food and resources, the tendency to form large flocks decreases, and territoriality can still exist as smaller family groups or flocks with only a single alpha male form to defend the resources.
If the habitat is of lower quality, and food and other resources are less abundant, the tendency to form larger flocks increases to take advantage of the strength in number principle. Another interesting point is in habitats that are very limited in resources, birds will tend to form flocks that are more diverse in nature, composing of many different species and not many individuals of the same species. This is because different species tend to have different modes of foraging or locations where they forage, known as a foraging niche. Being in a flock with different species will decrease the competition with others who have the same foraging niche.
The composition of species within the flock can also influence how and where certain species forage. For instance in a flock composed of Black-capped Chickadees and Tufted Titmouse, the Tufted Titmouse are a dominant species, typically foraging lower along the forest floor and low branches. Black-capped Chickadees are then found higher in the trees, forced higher due to the dominance of the Tufted Titmouse. Now if White-breasted Nuthatch are found within that same flock, the Black-capped Chickadees will actually move lower in the trees to forage closer to the nuthatches. There are a few hypotheses for this behavior. It could be that the nuthatches act as a buffer between the dominance of Tufted Titmouse toward chickadees, or it could be that the nuthatches are good sources of information for food that the chickadees work to move closer to them to capitalize on. Whichever the case, this knowledge can assist you in predicting where the birds may be likely to forage based on which species are found in the flock.
White-breasted Nuthatch about to take off and continue foraging.
Next week we will discuss the second immediate benefit of these flocks, predator detection, and then look at the long-term benefits of winter flocking behavior and how it plays a role in breeding success for the following year.
Until next time,
Todd