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Earlier Laying, Larger Clutches and Better Habitat Were Linked to Higher Western Cattle Egret Breeding Success

Western cattle egret in breeding plumage sitting on a stick nest
Research: Reproduction & development, Ecology

A five-year study of Western Cattle Egrets (Ardea ibis) in Numidia, northeastern Algeria, found that breeding performance varied strongly among colonies and years and was linked more closely to habitat quality, breeding timing and clutch size than to nest dimensions. Fieldwork from 2003 to 2007 monitored 1,779 nests in the region’s long-established wetland breeding complex.

The researchers recorded laying and hatching dates, clutch size, egg measurements, nest height and diameter, hatching success and the number of young produced by successful nests. Clutch size was measured in 1,637 nests, hatching success in 1,332, and productivity in 781 successful nesting attempts. Egg laying extended from 22 April to 26 July, and mean clutch size across the study was 3.4 eggs.

Breeding performance differed sharply among sites and years

Hatching success ranged from 26.9% at Mekhada Marsh in 2005 to 82.6% at Dakhla in 2007, with an overall mean of 65.0%. Productivity also varied substantially. Lake Fetzara consistently had some of the highest values, with 2.6–2.7 young produced per successful nest in 2006 and 2007. Lake Tonga also reached 2.7 in 2003, although that estimate came from a smaller sample.

Lake Fetzara was characterised as a high-quality natural marsh, and reproductive success was positively associated with habitat quality. In contrast, nest height and external nest diameter did not explain breeding success. Nest height itself varied with the vegetation used as nesting support, showing that the birds adjusted nest placement to local colony structure without that structural variation translating directly into higher productivity.

Earlier laying and larger clutches were associated with better outcomes

Clutch size generally declined as the breeding season progressed, although the exact seasonal pattern differed among site–year combinations. Mean egg volume also declined with laying date. Hatching success fell later in the season at several colonies, including Lake Fetzara and Lake Tonga, and productivity declined through the season at Fetzara in 2006 and 2007 and at Chatt in 2006. Mekhada in 2005 showed the opposite productivity pattern, underlining that the seasonal effect was not identical at every site.

Across the study, breeding performance was negatively associated with laying date and positively associated with clutch size. Larger clutches could also produce large broods: at Lake Fetzara, one brood of six young and 15 broods of five young reached at least 12–15 days of age. The authors interpret the seasonal declines in egg volume, clutch size and hatching success as consistent with breeder age or body condition and with food becoming progressively more limiting later in the season. The high productivity at Fetzara suggests that favourable natural wetland habitat could support large broods.

Ectoparasites and poaching could disrupt whole colonies

The breeding landscape was dynamic, with colonies sometimes being abandoned or established between years. The authors identified an ectoparasite infestation at Dakhla in 2007 and intensive poaching at Sidi Achour in 2003 and Mekhada in 2005 as causes of severe disruption; at the poached colonies, thousands of clutches were destroyed. The paper also discusses adverse weather, predation, food availability and human disturbance as factors contributing to variation in reproductive outcomes.

These observations reinforce the difference between nest-scale measurements and colony-scale habitat quality. A nest could be built at a particular height or size without gaining an obvious reproductive advantage, while disturbance or deterioration of the broader breeding site could affect many nests simultaneously.

Mixed clutches revealed brood parasitism within and between heron species

The study also documented unusual clutch compositions. Western Cattle Egret clutches containing seven or eight eggs were interpreted by the authors as strong evidence of brood parasitism—the laying of eggs in another individual’s nest—between members of the same species. Mixed-species clutches showed interactions with three other herons in the breeding colonies.

Western Cattle Egret eggs were recorded in 17 Little Egret (Egretta garzetta) nests and 11 Squacco Heron (Ardeola ralloides) nests. Western Cattle Egret nests also served as hosts: four contained Little Egret eggs or young, two involved Squacco Heron, and one involved Black-crowned Night Heron (Nycticorax nycticorax). The authors describe these events as infrequent and report no measurable reduction in early chick survival from brood parasitism. They suggest that dense mixed colonies, competition for nest sites and the aggressive dominance of Western Cattle Egrets may help create the conditions for these interspecific interactions.

Overall, the study links reproductive performance to the quality and timing of breeding more strongly than to simple nest dimensions. The authors argue that protecting key wetlands in the Numidian complex, reducing disturbance during the breeding season and monitoring increasing reliance on human-derived food resources are important for understanding and managing the species’ continuing expansion into drier landscapes.

Sources and image credit

  1. Samraoui, F., Nedjah, R., Boucheker, A., & Samraoui, B. (2026). Ecological correlates of breeding success of Western Cattle Egret Ardea ibis in northeastern Algeria. Ostrich, 97(3), 223–233.Primary peer-reviewed article published online 2 July 2026. The five-year study monitored 1,779 Western Cattle Egret nests in Numidia. Breeding performance varied among sites and years, was negatively associated with laying date and positively associated with clutch size and habitat quality, while nest height and diameter did not predict reproductive success. The study also documented ectoparasite- and poaching-related colony disruption plus conspecific and interspecific brood parasitism.
  2. Samraoui et al. (2026), author-uploaded full textAuthor-uploaded final article used to verify the complete methods, sample sizes, site-level results, brood-parasitism records and discussion.

Image: Bonnie U. Gruenberg — Western Cattle Egret in breeding plumage on a nest in Florida, USA, 30 April 2012; Wikimedia Commons; CC BY-SA 3.0. Representative nesting image, not a bird from the Algerian study. · CC BY-SA 3.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

Reproduction & development

SPECIES IN THIS STORY

Species in this story

Western Cattle Egret Ardea ibis Explore species Little Egret Egretta garzetta Explore species Squacco Heron Ardeola ralloides Explore species

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