Purple Martin

The story of our largest swallow is a fascinating one. Purple Martins historically nested in natural cavities, such as those excavated by woodpeckers in dead trees. They still nest this way in the western United States but in the east they are now completely reliant on man-made housing. When this shift occurred is hard to determine, but there are early accounts by European settlers of Native Americans already using hollow gourds to attract martins to their settlements. Some have speculated that the indigenous peoples did this because of the insect-consuming prowess of the swallows, a popular perception that persists to this day.

Because Purple Martins are dependent on humans for their nest sites, they are also vulnerable to a lack of maintenance at these same sites. If a nest box is not cared for it will eventually deteriorate and become less suitable, or even worse attract non-native House Sparrows and European Starlings. Both these species are aggressive competitors for nest cavities which not only start nesting earlier but also will forcibly evict martins or destroy their eggs. For this reason, the “landlords” who maintain martin housing must make frequent visits to ensure their charges are safe from invasive intruders.

Despite this exceptional level of local protection, martin populations in the eastern United States are in decline. The reasons for this, as for other aerial insectivores, aren’t well understood, but could include threats on the South American winter range, unpredictable spring weather, or changes in prey availability. This decline has played out in New Hampshire in interesting ways. Once widespread in the central part of the state, the species was restricted to a handful of colonies in the Lakes Region by the early 2000s, and the last colony there was abandoned in 2017 after a long decline. At roughly the same time, a single pair was discovered in Seabrook, nesting, in of all places, a Tree Swallow box. A group of local volunteers rallied around this location, erected a new nesting structure, and have gradually increased our coastal population from this single nest to over 50 nests in five colonies by 2023. These birds are in good hands, but only from April to August, and unknown dangers await them elsewhere.

As for their reputed role as consumers of bothersome mosquitoes, the truth is that martins are not significant consumers of these insects. Although they prey on a wide variety of flying insects, they are usually much higher in the air than mosquitoes travel and feed entirely during the day when mosquitoes are far less active. Some of the most common prey items delivered to nests are larger species like beetles, dragonflies, bees, and flying ants.