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If you are a visitor to the River S unit, you have probably noticed the condominium at the entry when you are crossing over the bridge. OK, so it is a cluster of white gourds on a tall pole with lots of bird activity around. Kind of a bird condo. Five years ago, a team of volunteers started setting up the gourd houses to attract Purple Martins (Progne subis) into the refuge. There are currently seven set ups around the refuge, only one of which is easily seen on the auto tour. Five are used in a banding study.
The team, led by Randy Hill, erects and monitors our gourds along with clusters set up at Pierce and Steigerwald Refuges up the Columbia River, Port of Vancouver, on Columbia Land Trust lands and at Julia Butler Hansen Refuge down river. Not only do they erect the structures each spring, but they try to band each year’s hatchlings and then monitor the adults the next year. Timing is critical to success of the program. Other species like to use these gourds too so it is important to set them up just as the Purple Martins are coming into the area looking for nest sites. Too early and you are likely to get other intruders, such as European Starlings, House Sparrows or other swallows, who must be removed quickly as they will out compete the martins. Once set up, the team monitors the arriving adults and collects information on any birds that are banded. Then they wait for egg laying, hatching and enough time to pass for the hatchlings to be banded. The banding process includes dropping the gourd complex down, checking all the nestlings, banding them, recording data, returning the gourd to its higher position and retreating as quickly as possible for minimal disturbance to the birds. The process started June 27th this year. The banding age for nestlings is about 11-21 days old. Too young and the legs are not yet hardened and too fleshy for the band to fit around the leg; after 21 days, they risk the young pre-fledging from the gourd after their “big outdoors” experience. It took three days to monitor the 166 gourds this year.
Purple Martins nest almost exclusively in manmade boxes now. Their “natural” nest would be old woodpecker holes, but with the advancement of people across the country, they have become associated with human populations. In the time of J.J. Audubon, he noted that every good pub had a Purple Martin box. Only in the most remote areas of the martin’s summer range, do they still use woodpecker holes. A few of our Ridgefield pairs have also started nests in some of the Kestrel nesting boxes this year again. Perhaps the popularity of the many martin boxes near homes is related to their exclusive diet of flying insects. We only see the Purple Martins here in the summer, when flying insects are indeed plentiful. Cold and rain do not make for adequate food supplies for these birds. But interestingly, Purple Martins are high flyers compared to other swallows, flying up as high as 50 m, and they feed during the day. Our hope that they might bring down the mosquito populations, which are dawn and dusk flyers at low levels, is not to be realized.
Adult (2 years old or older) males arrive in early April to claim nests where they first nested, and adult females arrive shortly after but not necessarily where they first nested. Yearlings arrive about a month or more later and try to compete for what is left. Both males and females can nest as yearlings, but a large percentage do not and tend to be pioneering birds to new areas, or just hang out. Once the females arrive, pair bonds are established and the nest gourd is chosen. One pair will occupy a gourd. Unless there is an early failure of a nest, the Purple Martins will typically lay one clutch of 5 eggs, sometimes six. Later clutches may be less. In about 15 to 18 days of incubation, the hatchlings will emerge. The hatchlings grow rapidly and at the end of three weeks, could be six times their hatch weight. Although it hasn’t been definitively established, fledging from the nest occurs about 28 days after hatching when the young have lost a little of the baby weight. They follow the parents out of the nest to be fed by the parents for several more days before catching insects and feeding themselves. Purple Martins will flock up after the nesting season, finding an insect productive area to roost and feed. They are fueling up before the southern migration to areas of northern South America.
At River S, we know that some of the previously banded birds have returned to our refuge. As of June 27th this year at Ridgefield, Steigerwald and Pierce, all but one gourd had a complete Purple Martin nest with only two that didn’t yet have eggs or young in the nest. Stay tuned for more details as the nesting season progresses.