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Black-crowned Night Herons Had 87.7% Hatching Success Across Four Algerian Wetland Colonies

Black-crowned night heron arranging twigs in a tree nest
Research: Reproduction & development, Ecology

A five-year study of Black-crowned Night Herons (Nycticorax nycticorax) in north-eastern Algeria followed breeding at four wetland colonies from 2003 to 2007. Across 174 nests, the mean clutch size was 3.3 eggs and 87.7% of eggs hatched.

Among 105 successful nests, an average of 2.5 chicks were still alive at 12–15 days of age. The 87.7% figure therefore describes egg hatching, not the proportion of young that ultimately fledged. The herons generally began breeding earlier than other heron species in the mixed colonies and often nested higher within the colony structure, using both trees and reedbeds.

Breeding performance differed among colonies and years and was highest at Lake Fetzara, the largest wetland in the region. The authors interpret this as evidence that habitat quality within the regional wetland network matters for reproductive performance.

Clutch size itself remained relatively stable among colonies and years. Larger clutches were associated with more hatched eggs and more surviving chicks, while laying date and nest height did not clearly explain additional variation once clutch size was taken into account.

The authors also report that the regional Black-crowned Night Heron population had increased by about tenfold over the preceding decade. They nevertheless emphasise continuing pressure on both heron populations and wetlands and argue for continued monitoring and targeted conservation.

Sources and image credit

  1. Samraoui, F., Nedjah, R., Boucheker, A., & Samraoui, B. (2026). The Reproductive Ecology of the Black-Crowned Night Heron in Numidia, North-Eastern Algeria. Waterbirds, 49(1).Primary peer-reviewed study. Four mixed-species wetland colonies in north-eastern Algeria were monitored from 2003 to 2007. Mean clutch size was 3.3 eggs across 174 nests, hatching success was 87.7%, and 105 successful nests had an average of 2.5 chicks alive at 12–15 days. Breeding performance was highest at Lake Fetzara.

Image: Augustus Binu — wild Black-crowned Night Heron building a nest in Bangalore, India, 17 July 2015. Source: Wikimedia Commons. CC BY-SA 3.0. Representative nesting image; not a bird from the Algerian study. · CC BY-SA 3.0 · Source

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Reproduction & development

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