Sunday 13 December 2020

Sunday 13th December

A completely different day to yesterday's weather with a lively Force 5-6 southerly, milder (12°C) and dank with nearly constant mizzle or heavier bursts of rain all day. A 1½ hour seawatch from first light was productive with 163 Gannet, 50 Kittiwake, 20 auk spp. (mostly Razorbill); five Red-throated Diver, two Common Scoter, a Great Northern Diver, a fw Mediterranean Gull and the highlight a Great Skua through at 08:26. A few waders also passed, c.45 Oystercatcher, likely on their way to the Teign Estuary and other exposed shorelines to forage on the dropping tide; 8 Curlew (destination unknown) and a Turnstone; everything flew SSW. A Kingfisher briefly perched on riprap below the lifeguard hut. 

A mixed feeding flock that moved through Entrance Bushes contained presumed long-stayers - the two Firecrest and the Siberian Chiffchaff. Also in sheltered parts of the woods, four Goldcrest, four Bullfinch, a Coal Tit and a Great Spotted Woodpecker. As expected, single-figures of Shoveler, MallardMoorhen and Water Wail and a single Little Grebe were on Main Pond or Entrance Pond.

WeBS sector counts were timed to cover the 17:23 tide (Exmouth Docks gauge), was more than a third of a metre higher than predicted (4.16 metres) and lapped  the foot of already undermined and degraded sea defences. The combination of windy conditions, disturbance and high spring tide at dusk saw some waterbirds seek refuge in The Bight and this is where most of the impressive counts of 365 Dark-bellied Brent Goose and 64 Great Black-backed Gull were; and also the second highest ever count here of 128 Shelduck

This species continues to increase here and that long-term trend seems to be influenced by shifts in the estuary's population. The first chart below plots average (not maximum) WeBS counts per decade for each month for the entire estuary. Visually, this suggests little change in numbers during the early part of the wintering season (Oct - Dec) but in the latter part of the winter season (Feb - Mar), since the 1960s to the present, population declines on the estuary become more pronounced * 

However, the picture is different at Dawlish Warren; its wintering population has generally increased or remained stable in every month (Oct - Mar) through the decades, but curiously as the winter progresses, two related but contrasting patterns emerge and this is shown in the second chart - one shows that Dawlish Warren holds a decreasing proportion of the estuary's Shelduck through the winter but over the decades since the 1980s (no data for 1960s and 1970s), proportions have become less small. Reasons for this are not yet known; what seems to emerge from this short analysis is that there are two interrelated factors benefitting Dawlish Warren's mid-winter population - in December, which despite it not being the peak count period for the estuary, it is the month when Dawlish Warren consistently supports the highest proportions of that estuary population (half of them in 2000s!); and whilst Jan - Mar is the peak count period for the whole estuary, despite long-term declines in those months, the proportions of those birds supported by Dawlish Warren has actually steadily increased in each comparative month over the decades. 

Population dynamics can be complicated but if by interpreting patterns that infers something about what the factors influence bird populations, then authorities can think about how best to direct resources for conservation outcomes on this internationally importance site.  

All this begins with raw data and that's down to the WeBS volunteers who braved the wind and rain today and on all previous count days, some of whom have done so for decades - we thank you.

* Note: that WeBS counts, or Birds of Estuaries Enquiry (BoEE) as it was known back in the 1960s and 1970s, did not conduct counts Apr to Aug so those are data gaps in the first chart below, not zeros; and sector data for Dawlish Warren is unavailable for those decades, hence missing from the second chart.

Data capture, analysis and presentation - Ivan Lakin

Off site, 33 Cattle Egret were again in fields on Easter Hill, north of Cockwood Marsh in the afternoon.

No comments:

Post a Comment