State of the Birds

Invasives

Threats to New Hampshire’s Birds

The flora and fauna of New Hampshire today are very different from when European colonists first set foot in what we now call New England. In the centuries since, numerous non-native species have been brought over – both intentionally and unintentionally – from all corners of the globe, often with detrimental effects on native ecosystems. Such invasive species can include plants, animals, and even diseases, each with different potential impacts on bird populations.

Emerald Ash-Borer, a native of east Asia, was first detected in NH in 2013 and has gone on to kill large numbers of ash trees across its still-expanding range.
Emerald Ash-Borer, a native of east Asia, was first detected in NH in 2013 and has gone on to kill large numbers of ash trees across its still-expanding range.
While Oriental Bittersweet can provide food and shelter for birds, the plant can quickly overwhelm native plants and is now banned from sale in New Hampshire. Photo credit: Pam Hunt
While Oriental Bittersweet can provide food and shelter for birds, the plant can quickly overwhelm native plants and is now banned from sale in New Hampshire. Photo credit: Pam Hunt

Plants

Some invasive plants are best known for their ability to outcompete native species and come to dominate a habitat (think of bittersweet tangles and barberry thickets). In such cases, habitat may be subtly changed to make it less suitable for nesting or foraging birds. Fruit produced by non-natives is not always as nutritious as natives, and non-native plants also support fewer insect species. Planting native species and removing invasives are two of the best things you can do to make your yard a better place for birds. In wetlands, invasive plants can completely alter the original habitat, such as when dense stands of Phragmites replace native salt marsh along the coast. Cleaning and checking boats is a recommended practice to reduce the chance of moving invasive plants from one wetland to another.

Animals

Some of the first non-native species animals brought to this continent were birds – think of the famous story about starlings and a New York Shakespeare afficionado. Starlings and House Sparrows both outcompete native cavity-nesting birds for nest sites, and the sparrow in particular is a significant threat to Purple Martins and Cliff Swallows. You might not know that the House Finch is also not native (they were released in New York City in 1939) and have been implicated in Purple Finch declines during the 1980s and 1990s. Some introduced animals are predators, and the most detrimental of these in New Hampshire is the domestic cat. And then there are all the insects, which have the potential to alter plant species composition by selectively feeding on their preferred hosts. Non-native insect pests are now causing mortality in New Hampshire’s hemlock and ash trees, although any impacts on birds from the loss of these common trees remains to be determined.

Non-native House Sparrows are known to take over Cliff Swallow nests and evict eggs and chicks. Photo credit: Pam Hunt
Non-native House Sparrows are known to take over Cliff Swallow nests and evict eggs and chicks. Photo credit: Pam Hunt
NH population trend for House Finch. Finches were initially introduced to the Northeast US in 1939 and expanded rapidly. In 1994 a new disease appeared and disproportionately affected them, resulting in a steep decline from which they have not recovered.
NH population trend for House Finch. Finches were initially introduced to the Northeast US in 1939 and expanded rapidly. In 1994 a new disease appeared and disproportionately affected them, resulting in a steep decline from which they have not recovered.

Diseases

Just as with plants and animals, bacteria, viruses, and other pathogens can have direct and indirect effects on birds. Direct effects occur when the pathogen causes excess mortality, as was the case with West Nile Virus and crows in the early 2000s and conjunctivitis in House Finches in the 1990s. New diseases are always a risk, and in the 2020s a deadly strain of avian flu started being detected in waterfowl, other water birds, and the scavengers such as vultures and eagles that fed on carcasses. Because many dead birds are hard to find, the overall effects of disease on their populations is difficult to measure. Pathogens can also alter habitats, as the almost complete loss of American Chestnut to a fungus by 1940 can attest. It’s impossible to know how the disappearance of chestnut affected bird populations, but as new diseases and pests emerge we might have a chance to see this process in action once again. You can help prevent introducing invasive insects or pathogens into new areas by observing measures such as firewood transportation bans.

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Information for the species profiles on this website was compiled from a combination of the sources listed below.

  • The Birds of New Hampshire. By Allan R. Keith and Robert B. Fox. 2013. Memoirs of the Nuttall Ornithological club No. 19.

  • Atlas of the Breeding Birds of New Hampshire. Carol R. Foss, ed. 1994. Arcadia Publishing Company and Audubon Society of New Hampshire

  • Birds of the World. Various authors and dates. Cornell Laboratory of Ornithology.

  • Data from the Breeding Bird Survey

  • Data from the Christmas Bird Count