The Winter Bird Population of The King's Forest

THE WINTER BIRD POPULATION OF THE KING'S FOREST A . J . LAST

Introduction BIRD populations of woodlands in winter have been little studied.

The present paper summarizes work carried out in The King's Forest, north-west Suffolk, between November, 1975, and March, 1976, with a view to establishing the composition of the winter bird Community of the area, the relative abundance of the species present, and the population level during the winter.

The Habitat The plantations of The King's Forest cover an area of 2,185 hectares (5,399 acres). The Forestry Commission acquired the area in 1935, planting commenced the following year, and 99% of the planting had been completed by 1952, so that at the time of the study the area was a mature forest, consisting of 53% Corsican pine, 25% Scots pine, 2% larch, 3% other conifers, and 17% broad-leaved species (largely birch, oak, and beech). The broadleaved species, especially birch and beech, were planted in narrow belts along the rides and the public roads within the forest.

The dense canopy of the pines and the litter of the pine needles on the ground virtually exclude other forms of Vegetation except grasses, and only along the rides and margins of the forest are grasses and bracken prominent.

The Transect The winter bird population was sampled by making counts along a transect route 8.25 kilometres (5.1 miles) in length between November, 1975, and March, 1976. The transect route followed existing forest rides, mainly intersecting the mature pine plantations, but also crossing the birch belts at several points and abutting on one area of young pines approximately six feet in height.

14 counts were made, as follows: weekly counts during November and December; fortnightly counts during January, February and March.* Each count took approximately 2 hours 45 minutes, and all the counts were made within the period 1000-1400 hrs. G.M.T. during fairly calm and dry weather.

Species Composition and Relative Abundance The Table, which is based on the 12 winter counts (November-February), shows the species composition of the winter • I n view of the length of the transect, fortnightly counts during the whole period would have been sufficient for the purpose of the study: more frequent counts were made during November and December only because more time was available to the observer during those two months.

Suffolk Natural History, Vol. 17, Part 3

198

bird population of the forest and the relative abundance of the species present. 41 species were recorded, 18 of which attained at least 1 % of the total population recorded.

Three species, namely goldcrest, coal tit, and blue tit, collectively accounted for 47% of the total winter population. That figure becomes 52% if three species almost exclusively associated with the birch belts—viz, redpoll, siskin and bullfinch—are excluded from the total.

TABLE

Species

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

Goldcrest Coal tit Blue tit Wren Blackbird Long-tailed tit Great tit Redpoll Greenfinch Siskin Bullfinch Pheasant Chaffinch Marsh tit Jay Robin Dunnock Wood pigeon

Species comprising, individually, 19. Crossbill 20. Redwing 21. Great spotted vvoodpecker 22. Treecreeper 23. Yellowhammer 24. Red-legged partridge 25. Green woodpecker 26. Goldfinch 27. Skylark 28. Willow tit 29. Linnet 30. Carrion crow 31. Woodcock 32. Nuthatch 33. Meadow pipit 34. House sparrow 35. Song thrush 36. Fieldfare 37. Magpie 38. Mistle thrush 39. Starling 40. T r e e sparrow 41. Kestrel

Number of Counts during which species was observcd 12 12 12 12 12 12 12 11 12 9 12 12 11 12 12 10 10 11

Total

731 653 505 273 270 225 152 125 120 116 106 94 81 74 67 59 51 40

less than 1% of the total.

33 9 32 5 21 10 11 6 11 6 11 2 10 8 10 4 10 3 5 9 9 3 7 5 5 5 5 3 4 4 4 3 4 2 1 3 2 2 1 2 1 2 1 2 1 1

Percentage 18.51 16.5 12.8 J 6.9 6.8 5.7 3.8 3.2 3.0 2.9 2.7 2.4 2.1 1.9 1.7 1.5 1.3 1.0

THE WINTER BIRD POPULATION OF THE KING's FOREST

199

Population L e v e l DĂźring the Winter T h e totals for each of the 14 counts are plotted on the graph shown in FIG. 1, which thus gives an indication of the trend in the total bird population of the forest during the course of the winter. Since the study was concerned mainly with the birds of the pines, the figures for the three birch-frequenting species mentioned above are not included in the totals appearing in FIG.

F sc;, i

200

Suffolk Natural History, Vol. 17, Part 3

The late-November peak shown in FIG. 1 was due Iargely to the high numbers of the three most abundant species of the winter, viz, goldcrest, coal tit, and blue tit (see FIGS. 2 and 3), which collectively accounted for 59% of the total. It is not possible to say whether the high numbers resulted from real influxes of birds into the forest or whether they were a merely fortuitous result of birds moving through the plantations in search of food. Whatever the explanation, at the time of the next count, nine days later, the numbers of goldcrests and blue tits had fallen sharply (see FIG. 2) and only the coal tit remained at a high level (see FIG. 3).

THE WINTER BIRD POPULATION OF THE KING's FOREST 201

FIC, O

COÂŤ.

Although there were twice as many counts in NovemberDecember than in January-February, it is evident from Fig. 1 that, notwithstandingfluctuationsduring thefirsthalf of the winter, the general trend in the total population during the winter period was one of decline. The decline accelerated in the second half of January, the lowest population being reached in the second half of February.

It is tempting to link the decline from late January with the spell of severe weather which occurred during late January-early February. The February counts for both coal tit and blue tit were indeed low: see Figs. 2 and 3. On the other hand, although the late-February and March counts for the goldcrest were very low, the early-February count for the species was remarkably high: see Fig. 2.

Whatever the true effect of the cold spell, the low total population of late February and early March (see Fig. 1) was doubtless due in part to the departure of winter visitors, including the majority of the blue tits, wrens, blackbirds, long-tailed tits, and great tits.

Finally, the high count at the end of March (see Fig. 1) was due to the abundance offivespecies, i.e., chaffinch (78), coal tit (52), wood pigeon (52), pheasant (29), and greenfinch (28), the high numbers of chaffinches, wood pigeons and pheasants reflecting influxes of those species into the plantations for the

202

Suffolk Natural History, Vol. 17, Part 3

breeding season. The count for the chaffinch was only three short of the winter (November-February) total for the species, while the count for the wood pigeon exceeded its winter total by a dozen.

Acknowledgement I am grateful to S. Chapman, Chief Forester, Forest Office, West Stow, for information about the forest.

A. J. Last, 130 Fornham Road, Bury St. Edmunds, Suffolk.