White Ibis

It used to be that a flock of White Ibis rising from a marsh was an unexpected delight, rarely experienced. This species arrived on a rising tide of southern waterbirds advancing northward, with the first documented breeding record in 1977 of a single pair on Fisherman Island National Wildlife Refuge (NWR), Northampton County (Rottenborn and Brinkley 2007). Populations expanded rapidly in number and distribution, likely fueled by post-breeding dispersal (Heath et al. 2020). Today, White Ibis are an increasingly observed species in coastal Virginia, where their circling flocks of bright white adults and patchy brown-and-white juveniles are a more expected but no less exciting sight.

Breeding Distribution

The White Ibis was well-covered during the Second Atlas by the 2018 Virginia Colonial Waterbird Survey, a coastal census conducted by the Center for Conservation Biology in collaboration with the Virginia Department of Wildlife Resources and The Nature Conservancy. The survey identifies nesting locations of this and other species that breed in colonies. Because the White Ibis only breeds within the survey area, there was no need to model its distribution. For information on where the species occurs in Virginia’s Coastal Plain, please see the Breeding Evidence section.

Breeding Evidence

The White Ibis nests exclusively within the survey area covered by the Virginia Colonial Waterbird Survey in 2018, and this survey documented the locations of breeding colonies of this species. Therefore, the species is unlikely to have nested in blocks without confirmed breeding evidence. Additional breeding confirmations were reported by Atlas volunteers in other years of the Second Atlas period.

The White Ibis breeds in mixed-species rookeries on the Eastern Shore barrier islands. During the Second Atlas, breeding was confirmed in three blocks in the two counties on the Eastern Shore (Northampton and Accomack; Figure 1). It bred on Wreck Island and Cobb Island and along the Chincoteague causeway. Other Atlas confirmations outside of these nest sites were from recently fledged young away from the nest. Not captured by the Atlas were recent colonies in mixed-species rookeries on Chimney Pole Marsh, Ship Shoal Island, Tangier Island, and Watts Island (Watts et al. 2019, 2024).

During the First Atlas, the species was only confirmed breeding at the southern tip of Northampton County, from which it has since expanded (Figure 2). However, White Ibis no longer breeds on Fisherman Island NWR where it was first recorded, as that rookery was abandoned in 2002 (Watts et al. 2024).

As an uncommon colonial nesting waterbird, White Ibis are difficult to observe for all but researchers and boaters. That said, they can sometimes be observed feeding in saturated agricultural fields and wet lawns. Only one observation of a nest with eggs was recorded on June 25, likely well into the breeding season (Figure 3). Young were observed in the nest until July 31. Additionally, there were observations of this species’ breeding behaviors during the 2018 and 2023 coastwide colonial waterbird surveys. For more general information on the breeding habits of the White Ibis, please refer to All About Birds.

Figure 1: White Ibis breeding observations from the Second Atlas (2016–2020). The colored boxes illustrate Atlas blocks (approximately 10 mi² [26 km²] survey units) where the species was detected. The colors show the highest breeding category recorded in a block. The numbers within the colors in the legend correspond to the number of blocks with that breeding evidence category. Nesting is unlikely outside of confirmed blocks.

Figure 2: White Ibis breeding observations from the First Atlas (1985–1989). The colored boxes illustrate Atlas blocks (approximately 10 mi² [26 km²] survey units) where the species was detected. The colors show the highest breeding category recorded in a block. The numbers within the colors in the legend correspond to the number of blocks with that breeding evidence category.

Figure 3: White Ibis phenology: confirmed breeding codes. This graph shows a timeline of confirmed breeding behaviors. Tick marks represent individual observations of the behavior.

Population Status

The White Ibis had too few detections during the Atlas point count surveys to develop an abundance model. However, the distribution and size of White Ibis colonies derived from the 2018 Virginia Colonial Waterbird Survey are displayed on the CCB Mapping Portal.

After its discovery as a breeder in 1977, the Virginia Colonial Waterbird Surveys show that the species increased to a high of 1,746 estimated breeding pairs in 2018 (Watts et al. 2019). From there, populations declined slightly, down to 1,602 pairs in 2023 (Watts et al. 2023). The long-term occupancy of wading birds in marsh-nesting colonies has caused some vegetation damage, which, alongside marsh subsidence, may explain this slight decrease. That said, White Ibis are one of the few waterbird species that nests on the ground in Phragmites australis patches. The nests and young seem to benefit from the almost 100% cover this invasive plant provides.

Figure 4: White Ibis population trend for Virginia’s Coastal Plain. This chart illustrates the number of breeding pairs as estimated by the Virginia Colonial Waterbird Survey (Watts et al. 2024). A data point is not included for 1998, as the Survey covered a smaller geographic area in that year. The vertical light blue bars represent the periods corresponding to the First Atlas (1985–1989) and Second Atlas (2016–2020).

Conservation

The White Ibis is not a species of conservation concern in Virginia. Protection of mixed-species rookeries can benefit White Ibis alongside species of concern such as Glossy Ibis (Plegadis falcinellus). Tidal flooding, marsh subsidence, and sea-level rise are threats already affecting some breeding colonies. Potential future management may include the protection of suitable inland marshes to replace lost coastal sites.

Interactive Map

The interactive map contains up to six Atlas layers (probability of occurrence for the First and Second Atlases, change in probability of occurrence between Atlases, breeding evidence for the First and Second Atlases, and abundance for the Second Atlas) that can be viewed one at a time. To view an Atlas map layer, mouse over the layer box in the upper left. County lines and physiographic regional boundaries (Mountains and Valleys, Piedmont, and Coastal Plain) can be turned on and off by checking or unchecking the box below the layer box. Within the map window, users can hover on a block to see its value for each layer and pan and zoom to see roads, towns, and other features of interest that are visible beneath a selected layer.

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References