Birds of Prey in Ireland
About 100 years ago, Ireland was devoid of large birds of prey like buzzards, red kites and golden eagles. Their populations were decimated by human persecution, but thankfully these mighty predators are starting to make a comeback thanks to environmental protection, the banning of poisons like strychnine, successful reintroduction programmes, and natural recolonizations. Unfortunately though, we do still regularly hear of cases where raptors are illegally shot and poisoned.
My First Sightings of Buzzards and Red Kites
One of the first places I ever saw buzzards and red kites was in Wales when I first visited in 2011. I was amazed to see multiple pairs of these majestic birds soaring high in the sky. While driving through mid and North Wales, we used to play ‘spot the buzzard’, and count the number we saw. I think our highest count was 30 in a single day. It got even more exciting when we spotted a red kite, which can be recognised by the V-shaped fork in its tail. It wasn’t long after that I started to see buzzards crop up in Ireland, which have naturally recolonized from Britain, and red kites now too following a successful reintroduction in Wicklow and waves of natural recolonizations from Britain.
During one of these visits to Wales, we visited the red kite feeding station near Aberystwyth called Bwlch Nant yr Arian, where as many as 150 kites flock to be fed! It is an amazing spectacle to witness, and an excellent tourist attraction for the region that supports quite a few local jobs. When I was there, I was even fortunate to see the white one, caused by a genetic mutation called leucism. But supplementary feeding in itself isn’t natural, and I sometimes wondered what the effect, if any, such feeding strategies might have on the overall health of the population? And what are the potential consequences to the wider environment, if supplementary feeding is leading to an artificially inflated local raptor population?
Supplementary Feeding Experiment
Eimear Rooney and colleagues from Queen’s University Belfast aimed to investigate that very question in a new study examining the effects of supplementary feeding on the common buzzard population in Northern Ireland. The study has recently been published in the international ornithology journal, Ibis.
Rooney and colleagues focused on mainly agricultural land consisting of improved grassland, but they also included areas of lower productivity such as bogs, rough grazing areas, woodlands and urban areas. Forty nests were located and monitored for a year prior to their experimental study.
For the experimental study, the nests were randomly assigned to four experimental study groups where the breeding pairs were (1) fed 35 days before they laid their eggs; (2) fed after their eggs hatched for 35 days; (3) fed throughout the breeding season for a total of 70 days; and (4) a control group that were not fed at any stage during the study.
The supplementary food items included woodpigeon and rabbit, prey items that Rooney previously found to be regularly consumed by buzzards in the area.
Rooney found that feeding buzzards prior to egg laying only resulted in a marginal increase in the overall clutch size, but found no overall difference in the weight of the chicks, hatching success or fledging success. However, the quality of the surrounding habitat appeared to have the greatest overall effect on the breeding success, as the buzzards delayed laying their eggs in marginal habitat areas such as bogs, scrub and rough/unimproved grassland, that Rooney believes is a consequence of fewer rabbits (one of the preferred prey items) in such areas.
Rooney suggests that in areas where game birds for instance are reared, and where buzzards might potentially predate on them, diversionary feeding for buzzards is unlikely to cause the population to rapidly expand beyond normal predictions. However, this is only in areas where prey isn’t limited already i.e. improved grassland where rabbits are abundant. However, in poor habitat e.g. bogs, rough grassland, and upland moors where red grouse are present, Rooney predicts that the benefits of diversionary feeding could be offset by the fact that the buzzard population in these areas could increase due the higher availability of food.
Rooney E, Reid N and Montgomery I (2014). Supplementary feeding increases Common Buzzard (Buteo buteo) productivity but only in poor-quality habitat , Ibis, DOI: http://dx.doi.org/10.1111/ibi.12218.