As much as I love to see the stark white CATTLEEGRETS with their livestock, as we drive by the vast green pasture lands of the Big island, I read they are nest predators, stealing eggs and chicks of native birds, namely the Hawaiian duck (Koloa), Hawaiian stilt (Aeo), Hawaiian moorhen (Alae ula), and Hawaiian coot (Alae Keokeo).
Yes, they do keep the flies, ticks and insects down, but there is more to the story. The egret, native of Africa and Asia, were introduced to the Hawaiian Islands in 1959 by the Board of Agriculture and Forestry, in conjunction with local cattle ranchers to try and combat flies that were affecting cattle herds. Flies were responsible for low weight gain in the cattle as well as damaged hides.
The original intent was to use the birds as biological control agents, but instead these birds have joined the long list of introduced species, that having failed their original objective, have caused a bigger problem, ie. disruption to indigenous fauna.
Since 2017 the cattle egrets have been culled, and while this elegant bird provides a service to the livestock, its relationship to endemic species remains problematic.
As we drive we can see the elegant birds with the dark cattle, by the dozens, and sometimes they are seen on the back of horses, donkeys, goats, and even sheared sheep.