Bye bye birdie? Part II

In Part I, you examined the patterns of total bird abundance at Hubbard Brook Experimental Forest. The data showed total bird numbers have declined since 1969, but is this true for every species of bird? You will now examine data for four species of birds to see if each of these species follows the same trend.

Red-eyed vireo in the Hubbard Brook Experimental Forest

Red-eyed vireo in the Hubbard Brook Experimental Forest

The activities are as follows:

It is very hard to study migratory birds because they are at Hubbard Brook only during their breeding season (summer in the northern hemisphere). They spend the rest of their time in the neotropics, or migrating back and forth between their two homes. Therefore, it can be difficult to tease out the many variables affecting bird populations over their entire range. To start, scientists decided to focus on what they could study, the habitat types at Hubbard Brook, and how they might affect bird populations.

Hubbard Brook Forest was heavily logged and disturbed in the early 1900s. Trees were cut down to make wood products, like paper and housing materials. Logging ended in 1915, and various plants began to grow back. The area went through secondary succession, which refers to the naturally occurring changes in forest structure that happen as a forest recovers after it was cut down or otherwise disturbed. Scientists knew that as the forest grew older, its structure changed: trees grew taller, and there was less shrubby understory. Today, the forest has grown back. It contains a mixture of deciduous trees that lose their leaves in the winter (about 80–90%; mostly beech, maples, and birches) and evergreen trees that stay green all year (about 10–20%; mostly hemlock, spruce, and fir).

Richard and his fellow scientists used their knowledge of bird species and thought that some bird species would prefer habitats found in younger forests, and others would prefer habitats found in older forests. They decided to look into the habitat preferences of four important species of birds: the Least Flycatcher, Red-eyed Vireo, Black-throated Green Warbler, and American Redstart and compare them to habitats available at each stage of succession.

  • Least Flycatcher: The Least Flycatcher prefers to live in semi-open, mid-successional forests. The term mid-successional refers to forests that are still growing back after a disturbance. These forests usually consist of trees that are all about the same age, have a thick canopy at the top with few gaps, an open middle canopy, and a denser shrub layer close to the ground.
  • Red-eyed Vireo: The Red-eyed Vireo breeds in deciduous forests as well as forests that are mixed with deciduous and evergreen trees. They are abundant deep in the center of a forest. It avoids areas where trees have been cut down, and does not live near the edge. After logging, it often takes a very long time for this species to return.
  • Black-throated Green Warbler: The Black-throated Green Warbler occupies a wide variety of habitats. It seems to prefer areas where deciduous and evergreen forests meet, and can be found in both forest types. It avoids disturbed areas and forests that are just beginning succession. This species prefers both mid-successional and mature forests.
  • American Redstart: The American Redstart generally prefers moist, deciduous, forests with many shrubs. Like the Least Flycatcher, this species prefers mid-successional forests.

birds

Featured scientist: Richard Holmes from the Hubbard Brook Experimental Forest. Data Nugget written by: Sarah Turtle and Jackie Wilson.

Flesch–Kincaid Reading Grade Level = 10.2

A view of the Hubbard Brook Experimental Forest

A view of the Hubbard Brook Experimental Forest

Additional teacher resource related to this Data Nugget:

There are two publications related to the data included in this activity:

  • Holmes, R. T. 2010. Birds in northern hardwoods ecosystems: Long-term research on population and community processes in the Hubbard Brook Experimental Forest. Forest Ecology and Management doi:10.1016/j.foreco.2010.06.021
  • Holmes, R.T., 2007. Understanding population change in migratory songbirds: long-term and experimental studies of Neotropical migrants in breeding and wintering areas. Ibis 149 (Suppl. 2), 2-13
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