Revisiting methods for estimating parrot abundance and population size

Abstract

Estimating abundance and population size is essential for many ecological and conservation studies of parrots. Achieving these goals requires methods that yield reliable estimates, but parrot traits can make them difficult to detect, count, and capture. We review established and emergent sampling and analytical methods used to estimate parrot abundance and population size, focusing on their assumptions, requirements, and limitations. Roost surveys are cost-effective if all roost locations in a region are known and stable, which is uncommon. Capture-recapture methods incorporate detection probability, but capturing, marking and resighting parrots can be difficult. Distance sampling estimates detection probability and surveys multiple species simultaneously, but is sensitive to the spatial distribution of individuals and excludes birds in flight. Roadside transects can cover large areas and survey multiple species, but habitats near roads may differ from the surrounding areas, biasing abundance estimates. Occupancy surveys and hierarchical models usually require spatially and temporally replicated datasets. Both allow estimation of detection probability; the former dispenses with count data, while the latter is a versatile set of methods that can incorporate multiple processes influencing detection and abundance. Finally, passive acoustic surveys can sample multiple species simultaneously, but identification of vocalisations can be difficult and time-consuming.

Autonomous sound recording outperforms human observation for sampling birds: a systematic map and user guide

“…Indeed, it can be challenging to measure abundance from sound recordings when large groups of animals are recorded (Denes et al. ), but this challenge is also present in bird point counts. More studies should test whether sound recordings can yield accurate abundance estimates.…”

“…Four of the publications included in our literature search estimated abundances from sound recordings (Hobson et al 2002Sedlacek et al 2015, Bombaci et al 2019, and they found that abundance estimates correlated strongly with those obtained from point counts, even though species occurring in flocks can be underestimated in sound recordings (Sedl a cek et al 2015). Indeed, it can be challenging to measure abundance from sound recordings when large groups of animals are recorded (Denes et al 2018), but this challenge is also present in bird point counts. More studies should test whether sound recordings can yield accurate abundance estimates.…”

Population monitoring and modelling of yellow‐shouldered parrot on Bonaire, Caribbean Netherlands

“…We collected the data in a manner that would allow the use of different count methods for detection and abundance estimation (e.g. 3-min snapshot counts, two 3-min timeremoval counts, or two-week repeated counts; Burnham et al 2004, Royle 2004, Buckland 2006, Nichols et al 2009, Rivera-Milán and Simal 2012, Amundson et al 2014, Buckland et al 2015; the methods were recently reviewed by Dénes et al 2018). However, because distance sampling is pooling robust, and our main interest was to estimate abundance across the entire survey region for population monitoring and modelling, we used multiple-covariate distance sampling to explore the influence of detection covariates, and conventional distance sampling to compare parrot mean density estimates at surveyed points after stratification (e.g.…”

Peer Review #1 of "Cities may save some threatened species but not their ecological functions (v0.1)"

“…Habitat use by parrots was assessed through large-scale roadside surveys, conducted under permits from the Ministry of the Environment of the Dominican Republic. Among different methods available to estimate parrot abundance, roadside surveys are recommended given that they allow to sample large areas and thus increase the likelihood of recording parrots, as they usually show low densities and aggregated distributions resulting from their highly-mobile and flocking behavior (Dénes et al 2018). This methodology has previously allowed the assessment of parrot abundances (Grilli et al 2012;Blanco et al, 2015;Tella et al 2016a;Baños-Villalba et al, 2017), of their foraging behavior (Tella et al 2016b, Montesinos-Navarro et al 2017, and of the effects of habitat loss and fragmentation in a variety of raptor and parrot species in different Neotropical biomes (Carrete et al, 2009;Tella et al, 2013).…”