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Causes of decline of ring ouzel populations

Male ring ouzel, Cairngorms National Park, Scotland

Male ring ouzel

Image: Andy Hay

Project objectives

  • To review the long-term trends in ring ouzel abundance across several areas throughout the UK
  • To understand the demographic mechanisms driving the population decline
  • To quantify the frequency of multiple brooding in ring ouzels
  • To test factors influencing the timing and causes of post-fledging mortality, and to quantify the timing and magnitude of local movements and dispersal
  • To understand seasonal variation in foraging conditions for ring ouzels in upland habitats, and their effects on juvenile habitat selection
  • To assess environmental correlates of territory occupancy rates and nest site selection
  • To test if food shortage during the summer results in lower ring ouzel nestling body weight at fledging, leading to subsequent lower post-fledging survival

Work planned or underway

The results of the feeding experiment (used to test if food shortage results in lower nestling body weight at fledging – see final project objective above) are currently being analysed.  Provisional results are expected by winter 2013/14.

Results

The number of breeding pairs of ring ouzels decreased by 44-100% during 1979-2009 across 13 study areas throughout the UK.

The population in an intensive study area in Glen Clunie, Aberdeenshire, Scotland decreased by 67%, from 39 to 13 breeding pairs, during 1998-2009.  Mean population growth rate calculated from annual censuses of the number of breeding pairs in this area was 0.91.  We recorded reproductive success, and used resightings of marked individuals to estimate survival rates in each year, thereby measuring the mean, variance and covariance among key demographic rates.  Prospective elasticity analysis indicated that mean population growth rate was most sensitive to adult survival.  However, integrated elasticity analysis, accounting for estimated demographic covariance, indicated that mean population growth rate was most sensitive to first-year survival.  Retrospective decomposition of variance indicated that first-year survival contributed most to observed variation in mean population growth rate.  However, adult survival was low compared with species with similar life histories

Sixty-one out of 108 (56.5%) individually marked females made two successful breeding attempts in one or more years during 1999-2011, but only two (1.8%) made three successful breeding attempts in one year.  These triple brooded females began breeding earlier in the season, and had shorter inter-brood intervals, than other females.  However, the impact of triple brooding on mean population growth rate in my study population was low.

Juveniles fledged from early-season broods had higher survival probability during each four-day period over 116 days post fledging (0.952 ± 0.011) than juveniles fledged from late-season broods (0.837 ± 0.021).  Predation was the main apparent cause of mortality.

Juveniles foraged on invertebrates in grass-rich areas during June to mid-July, but then switched to feed mainly on moorland berries in higher-altitude, heather-rich, areas during mid-July to early-September.  Thus, a variety of habitats providing different food types is required during the late summer.

The number of years that breeding territories were occupied during 2006-2011 was positively related to the proportion of heather within a 100m radius of the territory centre.  In addition, nest sites were located in areas with higher topographical variability at intermediate altitudes, and with higher proportions of burnt heather and grass, than unoccupied randomly located areas within the study area.  These results suggest that ring ouzel breeding areas are associated with a mix of heather, burnt heather and grass within a 100m radius of nest sites.


Gallery

Who to contact

Innes Sim
Conservation Scientist
E-mail: innes.sim@rspb.org.uk

Partners


Funding

Scottish Natural Heritage (2006-08)

Cairngorms National Park Authority (2007)

Scottish Ornithologists Club (2000-05, 2010 and 2013)


Bird guide

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