Dynamics of colonial settlements of grey heron (Ardea cinerea L.) and great egret (Ardea alba L.) and stages of great egret expansion on the territory of Ryazan and Yaroslavl regions

Abstract

We present detailed data on three colonies of grey herons and great egrets in the Ryazan and Yaroslavl regions. All colonies are located on the banks of water bodies, differing in the amount of water immediately under the nests, the character of vegetation, the number of birds and the ratio of heron species. In the Ryazan oblast, grey heron is seen to increase its abundance in one colony (from 15 nests in 2002 to 69 in 2017), in the other – abundance stays approximately the same throughout 2001–2017 (3–40 nests). Abundance of birds in the mixed heron­egret colony in the Yaroslavl oblast in 201–2017 was stable (60 nests of grey heron and 11 nests of great egret). In 2000’s grey herons were observed to arrive in the Ryazan oblast earlier (mid-­, late March) compared to 1950’s – 1960’s (early to mid­-April). Arrival of herons in the coast of Volga’s reach of the Rybinsk reservoir is of similar character. Data on various aspects of heron biology are given. We present information on the expansion of great egret in the Ryazan and Yaroslavl oblasts. Three stages are demonstrated: in the Ryazan oblast – single encounters (1962–1999), sporadic nesting of single pairs (2000–2014), annual stable nesting (from 2014 till present); in the Yaroslavl oblast – single encounters (1997– 2008), systematic encounters (2009–2014), nesting (from 2015).

Keywords

• great egret
• ardea alba
• grey heron
• ardea cinerea
• colony dynamics
• nest colonies
• expansion stages