| Oschadleus HD 2020 Variation in colony sizes of weavers from a citizen science project. Ostrich online
Download a pdf of the paper here (limited to 50 copies, thereafter email me for a copy)
A new paper describes the range of colony sizes in weavers, based on the citizen science project, PHOWN (PHOtos of Weaver Nests). The paper provides quantitative colony size data for 80 of the existing 117 weaver species. While there are sometimes enormous colonies, generally weaver colonies are small. The average colony size for most species (66% of the 80 sampled species) was less than 10 nests.
Six species had a mean colony size of >50 nests: Red-headed Quelea, Red-billed Quelea, Speke’s Weaver, Clarke’s Weaver, Chestnut Weaver, and Sociable Weaver (>50 nest chambers in this case). Even species that often breed in large colonies, may sometimes have small colonies or even one male with a single nest. The figure below shows that most weaver species tend to have small colony sizes on average, but there are quite a few species that do have quite high colony sizes on average.
Southern Masked Weavers colonies
The species with the most PHOWN records is the Southern Masked Weaver, with over 8000 records. Southern Masked Weavers usually have small single-male colonies, with less than 10 nests in a colony. Some colonies may attract a large number of males, and contain hundreds of nests in an area. PHOWN gives the following stats for this species:
Average colony size: 4.5 nests, s.d. = 6.1
Range: 1 – 165 nests
n=8020 PHOWN records with nest counts.
There is scope for more detailed analyses of colony sizes for this species due to the large sample size. Other weavers with large samples (over 300) in the PHOWN database are:
White-browed Sparrow-weaver, Cape Weaver, Village Weaver, Red-billed Buffalo-Weaver, Sociable Weaver, and Red-headed Weaver.
More than 23000 PHOWN records included nest counts – thanks to all the citizen scientists that contributed records to this Virtual Museum!
To take part, register and upload records at the UCT Virtual Museum web (read the “How to” pdf for help)
Colonial bird groups
There are about 140 passerine families (with some 6500 species). Only a few passerine families contain species that have highly colonial breeding: weaverbirds, icterids, Palmchat, starlings, crows, and swallows (Collias 1984c p250-1).
Of the non-passerines, some of the most important colonially breeding species are seabirds (most species), waterbirds (many species), vultures, monk parakeet.
Colonial species tend to breed in inaccessible, or protected, sites since their nests are conspicuous to predators. They defend a small area around their nest and birds of a colony share feeding grounds.
Most colonial species (other than weavers) are monogamous, while most colonial weavers are polygamous. In the weavers, however, the Sociable Weaver and Red-billed Quelea are monogamous and may be found in very large colonies.