In restoring critically endangered species, the initial aim is to address the proxim-
ate causes of population decline to prevent extinction and to boost numbers to a
more viable level, while the long-term goal is to address the ultimate cause of
decline and rarity, such as habitat destruction. Many projects flounder by failing
to differentiate between the proximate and ultimate limiting factors, because the
remedial actions required to address them are different.
12.3.1Supplemental feeding
Supplementary feeding has shown a range of effects upon wild bird populations,
including:
- Increasing the percentage of birds breeding
- Improving the productivity of individuals by inducing earlier laying, increased
clutch size, or increased chick survival - Improving juvenile and adult survival.
Such responses clearly demonstrate the importance of food supply in influencing
individual performance, and can in turn lead to increased numbers (Newton
1998). Not surprisingly, supplemental feeding has been a main component in
many bird restoration projects, often implemented alongside other measures. In
particular, it may help to support other forms of management. Some Mauritius
Kestrel pairs, that had been given foster young to rear, were provided with extra
food (dead passerines), which allowed them to rear larger broods than normal.
At Peregrine Falcon Falco peregrinusnests, when one of the pair was killed, the
partner still managed to rear the young when given dead Coturnixquail (Craig
et al. 1988; Walton and Thelander 1988).
The recovery of the central North America population of the Trumpeter Swan
Cygnus buccinatoris attributed to supplemental feeding during the winter. This
population declined to about 130 birds in the 1930s. The swans fed on sub-
merged aquatic vegetation and in late winter, when most ponds froze over, many
swans died from food shortages. Annual supplemental feeding of grain was
started in 1936. The level of winter mortality dropped dramatically and within
20 years the population had increased to about 600 birds (Archibald 1978a).
Winter feeding programs have also greatly benefited populations of cranes.
A nonmigratory population of Red-crowned Cranes Grus japonensisin southeast
Hokkaido was stable at about 30 birds. In the winter these cranes used to feed
along streams, but in the unusually cold winter of 1952 the streams froze and so
the cranes were given grain to prevent them from starving. This winter-feeding
became a tradition and within 15 years the population had increased to about
200 birds, and has stayed around that level ever since. Similar population
Broad population management approaches| 273