Comparing the results of recall surveys and standardized searches in understanding bird-window collisions at houses

Abstract

ABSTRACT. Every year a large number of birds die when they collide with windows. The actual number is difficult to ascertain. Previous attempts to estimate bird-window collision rates in Canada relied heavily on a prior citizen-science study that used memorybased surveys. Such an approach to data collection has many potential biases. We built upon this study and its recommendations for future research by creating a citizen-science program that actively searched for collision evidence at houses and apartments for an extended period with the objective to see how standardized approaches to data collection compared with memory recall. Absolute collision estimates as well as relative differences were compared between residence types in the two studies, and we found considerable differences in absolute values for collisions but similar rankings of collision rates between residence types. Collision recall rates in our study (56.5%) were very similar those in the prior 2012 study, where 50.5% of participants remembered a bird colliding with a window at some time in the past. Fatality estimates, however, were 1.4 times higher in the 2012 study than in our study based on standardized searches. Rural houses with a bird feeder consistently had the highest number of collisions. This suggests that memory recall surveys may be a useful tool for understanding the relative importance of different risk factors causing bird-window collisions. Comparaison des résultats de relevés fondés sur le souvenir et de recherches standardisées dans la compréhension des collisions d'oiseaux avec les fenêtres de maisonsRÉSUMÉ. Chaque année, un grand nombre d'oiseaux meurent à la suite d'une collision avec une fenêtre. Or, ce nombre d'oiseaux morts est difficile à établir. Au Canada, les essais antérieurs destinés à estimer le taux de collisions d'oiseaux avec les fenêtres reposaient grandement sur une étude à participation citoyenne qui utilisait des relevés fondés sur le souvenir. Ce genre d'approche pour récolter des données comporte de nombreux biais potentiels. À partir de cette étude et de ses recommandations pour des recherches futures, nous avons créé un programme de science citoyenne fondé sur une recherche active d'indices de collisions avec les maisons et les appartements sur une longue période; notre objectif était de comparer l'approche de collecte de données standardisée par rapport à celle reposant sur le souvenir. Les estimations absolues de collisions et les différences relatives ont été comparées entre les divers types d'habitation dans les deux études et nous avons trouvé des différences considérables dans les valeurs absolues de collisions, mais des différences relatives similaires dans les taux de collisions entre les deux types d'habitation. Les taux de collisions fondés sur le souvenir des citoyens dans notre étude (56,5 %) étaient très semblables à ceux de l'étude de 2012, dans laquelle 50,5 % des participants se souvenaient de la collision d'un oiseau avec une fenêtre à un moment donné dans le passé. Toutefois, les estim...

Use of bird carcass removals by urban scavengers to adjust bird-window collision estimates

“…The number of carcasses detected in the first 24 hours needs to be adjusted by 1.47 to account for removal by scavengers. Searcher error was not corrected for when determining our estimate because it was assumed that those homeowners who participated in the original study (Kummer et al 2016a) completed daily searches and did not miss any collisions while they were participating. Table 4.…”

“…Kummer et al (2016a) developed estimates of mortality based on the presence of bird feeders and whether the house was in an urban or rural setting. In calculating our estimate for Alberta, we used the mortality rate and the same parameters as our original paper but corrected for carcass removal rate, which was not done in the original study.…”

“…We used our carcass removal rate to adjust the bird-window collision fatality rates reported in Kummer et al (2016a). Kummer et al (2016a) developed estimates of mortality based on the presence of bird feeders and whether the house was in an urban or rural setting.…”

“…The 24-hour period was used because it was the interval that citizen scientists were asked to use when searching their house for birdwindow collisions (Kummer et al 2016a). We estimated the carcass removal rate using the method outlined in .…”

“…The second objective was to create a correction factor for carcass removal by scavengers when estimating bird-window collision mortality, and apply it to a yearly bird-window collision mortality estimate for houses in Alberta, Canada by using citizen science data that are specific to this region (Kummer et al 2016a). …”