Abstract from BTO Research Report No 405:

Newson, S.E., Noble, D.G. & Marchant J.H. (2005)

Waterways Breeding Bird Survey: preliminary analyses of mammal data 1998-2003

1. The Waterways Breeding Bird Survey (WBBS) was introduced in 1998 in collaboration with the Environment Agency’s R&D Programme. Although primarily introduced as a counterpart of the Breeding Bird Survey, to monitor riparian bird species and populations, WBBS observers also record the mammals that they see as they walk their survey stretch or determine their presence by other means. Although summaries of the WBBS mammal data are included in the annual reports, there have been no attempts to calculate population trends. In this report we assess the effectiveness of the WBBS for monitoring UK mammal populations in riparian habitat, particularly specialist riparian species such as Water Vole, American Mink and Otter that are not currently monitored reliably on annual and national basis by any survey.

2. Preliminary analyses of WBBS data for 1998-2003 for the three riparian species, Water Vole, American Mink and Otter demonstrate that at the present levels of survey effort, there is sufficient power to detect a 48% change in presence of these species on WBBS stretches. Whilst this is quite low, a relatively small increase in surveyed stretches can result in a large increase in power to detect change in presence. For example, with 300 WBBS stretches, the power would allow an 33% decline in their presence on WBBS stretches to be detected, whilst with 700 stretches, a 25% decline in these species should be detectable. Additional power to detect change in these species could be obtained through combining WBBS with BBS data for these species, although the level of additional power obtained would not be useful in isolation unless combined with an increase in survey effort. It is unlikely that trends at a Government Office region, Country or by Environmental Zone could be produced for these species.

3. Analyses of sightings data for non-riparian species suggest that the populations of Brown Hare, Rabbit, Roe Deer and Grey Squirrel along waterways could be monitored by the WBBS. However, trends in habitat that borders waterways may not be representative of overall UK trends. Two species, Rabbit and Roe Deer, show significant population changes between 1998 and 2002. WBBS and BBS show a similar declining trend in Rabbit abundance and an increasing trend in Roe Deer abundance during this period.

4. In addition to producing national trends in relative abundance from count data, waterwayspecific trends for Brown Hare, Rabbit and Grey Squirrel were produced for England, for Rabbit and Grey Squirrel in the westerly and easterly lowlands of England/Wales (zones 1 & 2) and for Brown Hare in the easterly lowlands of England/Wales (zone 1). There has been a significant decline in Rabbit in England and in the easterly and westerly lowlands of England/Wales during the period 1998 to 2003. However, these may not be representative of trends from all habitats.

5. For species that are not counted in sufficient numbers on WBBS stretches to assess change in abundance, there is potential for monitoring their change in presence. In this report we produce trends for Red Fox, Hedgehog, Mole, Brown Rat, Badger, Stoat and Weasel. For the most widely reported species, Mole and Red Fox, recorded on 30-50% of stretches, a decline of about 23-33% should be detectable. Hedgehog, Brown Rat, Badger, Stoat and Weasel were recorded on 10-15% of stretches, and would need to decline by 48-58% before a significant decline in the species were detected. The data collected since 2002 on the criteria for recording the presence of mammal species will need to be explore further to assess the reliability of trends produced from monitoring the change in presence on WBBS stretches. Trends for species such as Brown Rat, Stoat and Weasel should perhaps be treated with caution for this reason.

6. Whilst data for a number of additional species recorded by the WBBS are insufficient to calculate indices of abundance or presence/absence, these data may provide important information on their distribution and relative abundance. WBBS data may be important if combined with data from other surveys, especially for species that are poorly monitored by any existing scheme. Although coverage is likely to vary across surveys, this may be controlled for through the production of interpolated distribution maps.

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