Distance sampling as an effective method for monitoring feral pigeon (Columba livia f. domestica) urban populations

Abstract

a viable and efficient alternative to the traditional methods used to estimate feral pigeons 31 population size and to monitor trends.

Feral Pigeons: Problems, Dynamics and Control Methods

“…Unfortunately, while the development of pest control techniques for feral pigeons have involved a significant amount of research (see below), in comparison, research aimed to develop unbiased methods for estimating pigeon population size has aroused far less interest. Pigeons counts are intrinsically difficult both because of the characteristics of urban environments (complex structure and poor visibility) and of the pigeons themselves (clustered distribution and high density; Buijs & Van Wijnen, 2001;Giunchi et al, 2007b;Johnston & Janiga, 1995;Jokimäki & Suhonen, 1998). Probably for these difficulties, several authors adopted ad hoc and uncalibrated indexes of population abundance, such as: (1) counts of naturally occurring 224 flocks (e.g., Buijs & Van Wijnen, 2001;Haag-Wackernagel, 1995); (2) counts of birds attracted with food (Dobeic et al, 2011;Sacchi et al, 2002); (3) counts carried out by walking along a random sample of square, non-overlapping sampling units ('quadrat counts'; Senar, 1996;Sol & Senar, 1992).…”

“…While still widely used in wildlife management due to their relatively low costs, population indexes are however highly criticized because their critical assumption (proportionality between index and true population density) is usually violated in real situation (see Sutherland, 1996;Williams et al, 2002 and references therein). In the case of feral pigeons, this often led to the impossibility of an objective evaluation and quantification of the actual effects of most pest control programmes (see Giunchi et al, 2007b for further details). More reliable population estimates have been obtained by combining the quadrat counts with the use of 'correction factors', which take into account the imperfect bird detectability and are estimated by using a mark-resight procedure on a subsample of the study area (Sacchi et al, 2002;Senar, 1996).…”

“…More reliable population estimates have been obtained by combining the quadrat counts with the use of 'correction factors', which take into account the imperfect bird detectability and are estimated by using a mark-resight procedure on a subsample of the study area (Sacchi et al, 2002;Senar, 1996). In fact, this method can produce accurate results, but it is costly as it requires catching a significant number of birds, and entails that the correction factor is estimated for each condition, as the number of birds that will pass undetected in different surveys is variable, depending on the characteristics of the study area and on the density and behaviour of pigeons themselves (Giunchi et al, 2007b). Recently, Giunchi et al (2007b) proposed the use of distance sampling as a valuable alternative for estimating pigeons abundances.…”

“…In fact, this method can produce accurate results, but it is costly as it requires catching a significant number of birds, and entails that the correction factor is estimated for each condition, as the number of birds that will pass undetected in different surveys is variable, depending on the characteristics of the study area and on the density and behaviour of pigeons themselves (Giunchi et al, 2007b). Recently, Giunchi et al (2007b) proposed the use of distance sampling as a valuable alternative for estimating pigeons abundances. The method consists in counting pigeons on line-transects randomly distributed over the urban area and then adapted to the urban road network.…”

“…This means that any control programme aimed at significantly reducing pigeon population size has to calibrate the adopted index of abundance, in order to estimate correctly the population trend and thus to evaluate the effect of the control. Given the above consideration, distance sampling should be regarded as a rather promising approach for monitoring feral pigeons, also considering its relatively low operative costs (Giunchi et al, 2007b). Actually, it should be noted that in recent years distance sampling has been increasingly used for estimating bird population size in urban habitat (Fuller et al, 2009) and that the method has been included in the guidelines for managing feral pigeons by some Italian local administrations (e.g.…”