Glossy Ibis

Breeding season timing varies enormously across the species' global range: April–July in Spain's Doñana, May around the Black Sea, March–May in eastern North America, June–September in Cuba, late January in southern India, and October–February in Australia. Tropical populations time nesting to coincide with the rainy season, when shallow water and invertebrate prey are most abundant.

Colonies range from a few pairs to over 1,000, almost always in mixed-species assemblages with herons, egrets, storks, and spoonbills. The nest is a bulky platform of sticks, twigs, or reeds — the material depending on what is locally available — with a shallow central depression approximately 30 cm in diameter. It is positioned at least 1 m above water, and sometimes up to 7 m high in dense emergent vegetation, low trees, or bushes. The male collects most of the material; the female does most of the construction. Both sexes continue adding fresh green leaves and grasses after the eggs are laid.

Clutch size is typically 3–4 eggs, occasionally 1–5. The eggs are pale blue or pale green, measuring approximately 4.7–5.8 cm × 3.3–4.3 cm. Both parents incubate, with the female sitting more often — all night and for part of the day. Incubation lasts 20–23 days.

Chicks hatch covered in sooty-black down and are fed regurgitated food by both parents. At 2–3 weeks they begin leaving the nest to wander and climb nearby branches. First flight attempts occur at 4–5 weeks, and young fly well by 6–7 weeks. At this point they may accompany parents to feeding areas. Sexual maturity is not reached until approximately 3 years of age. One brood per year is typical.

In the wild, Glossy Ibises typically live 10–15 years, though survival rates vary considerably between populations and age classes. First-year birds face the highest mortality, particularly during their first southward migration and first winter in sub-Saharan Africa. Adults that survive to breeding age — reached at approximately 3 years — have significantly better annual survival prospects. The oldest confirmed wild individual in North America was at least 21 years old, banded in Virginia in 1971 and last recorded in 1992. In captivity, the maximum recorded lifespan is 26.8 years (AnAge database, Brouwer et al. 1994).

The main mortality factors include predation of eggs and chicks at the colony by large gulls, foxes, and raccoons; hunting pressure in parts of southern Europe (particularly Italy, despite legal protection since 1977); and collision with power lines and fences during migration. Pesticide and heavy metal contamination has also been recorded at elevated levels in Glossy Ibis tissues compared to some co-occurring species.

Wetland drainage that reduces food availability can affect body condition and survival, particularly in drought years. Compared to the closely related Eurasian Spoonbill, which can reach 30 years in captivity, the Glossy Ibis appears somewhat shorter-lived, though the difference may partly reflect the smaller number of long-term ringing studies. Sexual maturity at 3 years is relatively late for a bird of this size, suggesting the species invests in a prolonged period of learning and development before committing to breeding.

The Glossy Ibis is listed as Least Concern on the IUCN Red List, supported by an enormous global range — an extent of occurrence of roughly 180,000,000 km² — and a total population estimated at 1.1–3.3 million individuals (Wetlands International 2002). Partners in Flight estimates a global breeding population of approximately 820,000. Despite this, BirdLife International assessed the overall population trend as decreasing in 2024, though the species does not approach the thresholds for a threatened category.

Regional trends diverge sharply. Western Europe and North America are success stories: Spanish and French colonies have expanded strongly since legal protection was introduced, and North American populations grew by roughly 4.2% per year between 1966 and 2015. By contrast, populations in parts of south-eastern Europe and New York State have declined, and illegal hunting in Italy — despite the species being legally protected since 1977 — has kept breeding numbers there to just 10–50 pairs.

The primary threat globally is wetland loss and degradation: drainage for irrigation and hydroelectric schemes, grazing, burning, and increasing salinity all reduce the shallow-water habitat the species depends on. In Australia, diversion of water for irrigation has disrupted breeding in the Macquarie Marshes by restricting areas of shallow water.

Oil spills, pesticide contamination (studies have recorded elevated heavy metals and pesticides in Glossy Ibis tissues compared to some co-occurring species), and ditching of marshes for mosquito control add further pressure. Human disturbance of nesting colonies — from boating, fishing, and dredge spoil deposition — and predation by gulls, foxes, and raccoons also affect breeding success. Climate change is projected to alter wetland availability across the range and may drive further northward range shifts, particularly in Europe.

Courtship in the Glossy Ibis is an intimate, tactile affair conducted at close quarters within the colony. Males arrive at the breeding site first and establish small territories centred on a prospective nest site, defending these vigorously against rival males with upright threat postures and occasional bill-jabbing. Once a female approaches, the male's behaviour shifts from aggression to display: he bows repeatedly, stretching the neck downward and then sweeping it upward in a slow arc, while simultaneously erecting the scapular feathers to show off the iridescent wing surfaces to maximum effect.

If the female remains, the pair progresses to mutual neck-intertwining — each bird draping its long neck over the other's in a slow, synchronised movement — followed by allopreening, in which the birds groom each other's head and neck feathers with the bill tip. The head and neck are the one area a bird cannot easily preen itself, so this contact serves a practical function. It also reinforces the pair bond through repeated physical contact. Bill-rattling, in which the pair clatter their bills together rapidly while cooing, is the final stage of courtship and appears to signal mutual readiness to mate.

The cobalt-blue facial skin border intensifies noticeably during the breeding season, and this colour change is thought to function as a visual signal of breeding condition — the brighter the blue, the more physiologically ready the individual. Pairs are monogamous within a season, though long-term pair fidelity has not been well studied; both sexes do, however, show strong site fidelity, returning to successful colonies in subsequent years.

For most of British ornithological history, the Glossy Ibis was a trophy. Known in Norfolk as the "black curlew" — a name with roots in Anglo-Saxon literature — it appeared occasionally on the coasts and marshes of southern England, where it was routinely shot by collectors until the 1920s. The species was considered a rare vagrant throughout the 20th century, with records numbering in the tens most years.

The turnaround has been striking. From around 50 birds per year in the 1990s, annual totals climbed steadily, reaching over 220 individuals from 50 recording areas in 2022. Most sightings remain concentrated in southern England and Wales, with autumn the peak season, when post-breeding dispersal brings birds north from Iberian and French colonies. Ringed birds have been traced directly to Doñana in Spain and the Petite Camargue in France, confirming the source populations.

Breeding milestones have followed in quick succession. A pair attempted to nest in Lincolnshire in 2014 — the first such attempt in Britain — though the attempt was unsuccessful. In 2022, a pair fledged one chick at a Cambridgeshire wetland, the first confirmed successful breeding in recorded British history.

Small breeding groups are now established in Suffolk, Oxfordshire, and Rutland, and the species is on a clear trajectory of range expansion into Britain. Climate projections suggest this trend will continue as suitable wetland habitat becomes available further north. In Ireland, a few birds spend most summers at wetland sites, but breeding has not yet been confirmed.