The Glossy Ibis (Plegadis falcinellus) typically occurs in marshes bordering the Atlantic and eastern Gulf Coasts. Glossy Ibis are not found in Wisconsin every year, but in recent years it is not unheard of to have one or more wanderers show up at Horicon Marsh, often in the company of western White-faced Ibis (Plegadis chihi).
And so when 2 Glossy Ibis showed up in late May of 2019, we were not overly suspicious that they were nesting. Recent atlases for surrounding states and provinces, including Michigan, Minnesota, Illinois, Iowa, and Ontario contained no breeding records for Glossy Ibis (One summering bird in Iowa was coded as Possible).
So imagine our surprise when atlaser Aaron Haycraft turned up a family group in the Old Marsh Road area of Horicon Marsh! The juveniles can be identified by their lack of chestnut in the plumage, and also show white patches on the throat, which you can see on this photo from Portugal. Review of this summer’s records show consistent observations of 1–2 Glossy Ibis at Horicon (and occasionally a single White-faced).
The two juveniles (right) lack the chestnut tones on the body of the two adults (left).
White patches on the throat indicate the center bird is a juvenile.
Since Aaron’s observation, we’ve had additional checklists with photos showing the family group: here, here, and here. And have also discovered an earlier checklist showing a juvenile that we didn’t know about until Aaron’s report. If you’ve got some ibis photos from Horicon this summer check to see if you may have captured photos of the family group (the easiest field mark may be the color of the neck/breast/upper-back in good light: chestnut in adults but gray-green in juveniles) and upload them to the Atlas eBird portal!
Ibis are known for post-breeding dispersal, which causes us to be cautious with a record like this. However, the history of the pair at this site all summer, the distance from other known Glossy Ibis populations, and the fact this continues to be the only pair of ibis seen at the marsh seems to make it unlikely these are birds that just showed up from somewhere else. To our knowledge (please email us at atlas@wsobirds.org if you know of any closer record), the closest confirmed nesting for this species is on the Atlantic coast, over 700 miles from Horicon Marsh!
Despite the heavy birder coverage at Horicon, the nest presumably escaped detection earlier in the summer because there is a large area of inaccessible marsh. Ibis tend to nest in low shrubs or rushes, often in colonies with other species like night-herons or gulls. Atlasers Daryl Christensen and Sumner Matteson reported seeing the ibis pair heading over into the area of a night-heron colony at dusk, earlier in the summer, a possible nest site for them. After hatching, the juveniles spend their first weeks fairly close to the nest site before venturing out farther with their parents to forage.
Historically in the U.S., Glossy Ibis were primarily in Florida, but a rapid range expansion occurred through the 1970s, and they now breed as far north as Maine. However, since the 1970s, population trends are less clear, with some populations in the northeast declining. Habitat quality may be an important factor —Horicon Marsh features exceptional habitat for marsh birds — and it will be interesting to see if this is a one-off or the beginning of a nesting population of Glossy Ibis in Wisconsin.