Puffin
Puffin © Akinori Takahashi
Puffins with tree mallow in foreground
Puffins with tree mallow in the foreground
Dense stands of tree mallow on Craigleith
Dense stands of tree mallow on Craigleith

How does tree mallow affect puffins?

The number of puffins on the east coast of Scotland have dramatically increased over the last 40 years at a rate of 7-12 % per annum. Yet, for one of the largest colonies, Craigleith, this trend has recently been reversed with numbers dropping from 28,000 burrows in 1999 to only 14,000 in 2003.

Graph of puffin numbers

 

Figure 1. Development of puffin numbers in two of the largest UK colonies. Population development on the Isle of May is representative for the east coast of Scotland where the invasive plant tree mallow is absent or currently reaches only low density. On the nearby island of Craigleith, where tree mallow has become most prominent from 2000 onwards, puffin numbers have decreased sharply.

From: Harris MP, Wanless S, Murray S, Leitch, A and Wilson LJ. 2003. Counts of Atlantic puffin Fratercula arctica in the Firth of Forth, South-east Scotland in 2003. Atlantic Seabirds, 5,101-110.

 

A recent study on Craigleith has shown that the number of puffin burrows is strongly and negatively related to the cover of tree mallow (Fig. 2). In the absence of tree mallow, an average of 8.7 burrows were counted per 3 m x 3 m plot, equivalent to almost 1 per m2. In contrast, an average of 3.7 burrows were counted in mallow stands and a negligible number of burrows occurred in stands with > 40% tree mallow cover.

Graph of tree mallow cover and puffin burrow numbers

 

Figure 2. The relationship between tree mallow density and the number of puffin burrows in 3 m x 3 m plots on Craigleith.

From: Van der Wal, R. (2004). Investigation of the relationship between the invasive alien tree mallow (Lavatera arborea) and the atlantic puffin (Fratercula arctica) and trialling of control of the tree mallow on the island of Craigleith in the Firth of Forth (Forth Islands SPA). Report to Scottish Natural Heritage.