Counting Crows

A Study of Wales’ Second Largest Known Raven Roost

by Mark Evans

Raven by Sergey Yeliseev, on Flickr
Raven by Sergey Yeliseev, on Flickr

One morning, back in 2000, while walking, through the forestry to the West of Merthyr, I stopped to take stock of the bird species around me, when suddenly around fifty Ravens flew from one of the conifer blocks. Suspecting that these may have roosted there, I decided to return at dawn, to check and possibly count them. A few days later I did just that, though the count was secondary to the excitement and awe of watching these magnificent crows flying out in the pre dawn twilight. Since that time I have been counting them monthly, for my own satisfaction, though the records are also submitted to the local biodiversity records centre.

The reason for the existence of the roost is Bryn Pica refuse tip, in RCT, at which most of them forage and the counts follow a broad pattern, but vary considerably, depending on weather conditions. The Ravens start flying from 30 to 45 minutes before dawn, so visibility, during the early stages of the count is usually extremely tricky. They often start calling around ten minutes before starting to fly out, then, when the time arrives, they leave in groups of various sizes. It can take anything up to an hour for them all to leave, during which the excitement of individual groups leaving the roost is usually punctuated by long periods of inactivity and silence.

The roost seems to be more prone to low cloud and hill fog than most of the taller hills around it, which makes carrying out a successful count a bit hit or miss. Many is the morning I’ve travelled to the roost in the dark, only to find it clamped down with fog or cloud or had cloud descend while counting and had to give up and go home. So returning home after a successful count, the feeling is both of pleasure at the experience and relief at having completed it successfully. Over the years the patterns of behaviour have changed a little. The calling is fascinating to listen to, there being so many subtleties to the vocalisation. I’ve heard it said that the various calls can convey real meaning to other members of the roost and I can certainly believe that.

What is the purpose of all those counts? Are there any patterns or trends to be gleaned from the data? This isn’t really my field, though a glance at the count totals for the past ten years reveals an annual pattern and a broad trend. Each year the numbers of birds using the roost are at their lowest in the winter months, increasing gradually in the spring and early summer, rapidly increasing in the later summer period, before dropping away less steeply in the autumn. The late summer peak is caused by breeding pairs and their young joining the roost, though why the numbers then drop again so rapidly is a bit of a mystery. Why a peak not a plateau?

The trend in the number of birds using the roost over the ten years of the counts is generally a downward one, though whether this is a reflection of a similar downward trend in the local population of Ravens is unknown. I am aware that locally, the brood size of Ravens has decreased and this does seem to be reflected in my own observations of family groups in the late summer peak. Typically there will be two adults and one juvenile, whereas there would once have been two or three juveniles. I’ve always had a soft spot for Ravens. However the experience of counting them monthly for ten years has turned that into a love. Even having to get up at two thirty in the morning, in the summer months, to get to the roost in time, or sitting in subzero conditions in the depths of winter cannot take away the thrill and sense of awe I feel every time I count ‘my Ravens’.

Blaencanaid Raven Roost. Monthly Counts

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
2000 N/A N/A N/A N/A N/A N/A N/A N/A N/A 274 265 215
2001 119 218 146 89 No Access. Foot & Mouth Restrictions 146 89
2002 126 132 142 166 325 333 379 310 312 147 105 56
2003 108 102 128 158 199 208 175 199 57 38 51 44
2004 20 72 81 184 192 N/A 179 173 N/A 88 16 23
2005 54 42 62 121 117 170 175 N/A 201 137 105 129
2006 50 N/A 67 74 52 114 203 149 130 143 60 100
2007 58 42 90 74 92 170 N/A 163 158 104 79 46
2008 72 86 84 50 59 139 185 278 368 163 N/A 38
2009 32 79 65 102 97 N/A 88 344 103 162 72 76
2010 N/A 119 87 199 219 188 152 261 196 177 157 50

This article first appeared in Action for Wildlife, Merthyr Tydfil Biodiversity Newsletter, Winter 2011 ( and has been reproduced here with kind permission of Mark Evans and Carys Solman.