Magpies are not as bad as people may think
Magpies have a bad reputation in some circles in New Zealand as they have been seen chasing, attacking and even killing other birds, although the frequency in which they commit these attacks appears to be low. Furthermore, there is often a perception that magpies are excluding native birds from areas that may be suitable for nesting or feeding - a perception that had not been tested. In September 2006 a trial was conducted in the Te Pahu region to investigate whether magpies were excluding native birds, especially tui and kereru, from food and nesting trees. We thought that if magpies were having a negative impact on other birds, culling them around areas that may be preferred by native birds (i.e., bush remnants and gardens containing trees that provide both food and nest sites) would surely increase their numbers.
With a lot of help from residents living around the foothills of Pirongia, magpies were trapped and culled over a six week period at eleven sites. The numbers of all other birds in these areas was counted before and during this trapping operation to test our hypothesis. Birds from eleven other sites, where trapping did not occur, were also counted over this period to see if any recorded change in bird abundance was due to the magpie trapping, or some other unknown variable.
Over 170 magpies were culled during the six week trapping period. That is about 16 per site, although, there was considerable variation between sites as the range went from 5 magpies at one location to 40! Fortunately, this trapping had a negative effect on the magpie population in these locations and significantly fewer magpies were recorded during bird counts, which showed that it was possible to lower the numbers of magpies in localised areas by just using trapping.
When we looked at whether there were any increases in the abundance of native birds, we found no significant trends. On the whole, native bird numbers in areas where magpies were trapped showed a similar pattern to what was observed in areas where no trapping occurred. This has led us to conclude that magpies are more than likely not having negative impacts on other native birds. Having said this, previous research that we have conducted in this area has lead us to believe that magpie behaviour can be highly variable between individuals, and some can be highly aggressive while others very placid. Therefore, if you do notice the magpie pair in your area regularly chasing away other birds (or worse!), it may be a good idea to set a few traps to remove them. However, if your magpie pair are not doing anything naughty, then it would be better to leave them alone because magpies are territorial all year round, meaning that they will keep potentially aggressive magpies away.
I would like to sincerely thank all of those people that took part in the study by clearing magpie traps and/or allowing me to count birds on their properties. Without their help this project would not have been possible. I am still in the process of writing this work up for publication, so when this eventually happens, I will make it available to those that are interested.
Many thanks, Dai Morgan, Biological Sciences, University of Waikato
For more scientific information on magpies, click here for an article on the relative importance of Australian magpies as nest predators of rural birds in NZ by D Morgan, JR Waas and J Innes. click here for a paper entitled "Can redirected aggression explain interspecific attacks by Australian magpies on other birds?" by D Morgan, JR Waas and J Innes.