Worth the Effort? Rehabilitation Causes and Outcomes and the Assessment of Post-Release Survival for Urban Wild Bird Admissions in a European Metropolis

Abstract

Globally, millions of wild birds are admitted to rehabilitation centres each year. We analysed data on wild bird admissions at an urban rehabilitation centre in Berlin, Germany, collected over 20 years (2005-2024), aiming to (a) characterise admission causes and demographics, (b) investigate the rehabilitation duration and release probability across admission causes and systematic bird groups, and (c) assess post-release survival as a proxy for rehabilitation success. Longer rehabilitation durations were generally associated with orphaned birds and those in poor condition or who had had an infection. Orphans and birds with undetermined admission causes were most likely to be released. Birds that were admitted in poor condition were least likely to be released, which was particularly the case among Passerines. The monitoring of post-release survival through ring recovery data revealed higher recovery rates for larger birds but no informative value on post-release survival across species; thus, it did not represent an ideal measure of rehabilitation success in terms of the original objective. We conclude that the extent, outcome, and success of wild bird rehabilitation may depend on the initial cause of admission and may differ between bird groups. Advanced measures to assess post-release survival should be considered to allocate the limited resources and the conservation efforts of wild bird rehabilitation centres to birds of species and/or admission causes best suited to undergoing rehabilitation.

Keywords: admission cause; conservation; post-release survival; rehabilitation; wild birds; wildlife rescue centre.

Figure 1

Location of the study area and schematic representation of the rehabilitation process for wild birds admitted to the Wild Bird Rehabilitation Center of the NABU Berlin. (a) The study area (blue box) comprises the city area of Berlin in North-East Germany. (b) Schematic representation of the rehabilitation process, from the moment that a wild bird is found within the city area to the monitoring of the individual after release. Euthanasia, humanely inducing death in an animal with minimal pain and distress; FU Berlin, Freie Universität of Berlin; NWBRC, Wild Bird Rehabilitation Center of the NABU Berlin.

Figure 2

Admission causes for five groups of wild birds admitted to NWBRC between 2005 and 2024 (n = 5102). Admissions were grouped based on systematic bird groups (top left panels), and admission causes (bottom right panels), with the field size proportional to the share of all admissions per order or admission cause, respectively.

Figure 3

Predicted rehabilitation duration [days] for eight causes of wild birds being admitted to NWBRC between 2005 and 2024 (n = 3510). The underlying data set only included individuals who were released and thus represented the full rehabilitation process. Symbols represent estimates coloured and shaped according to the bird group, with error bars representing 95% confidence intervals.

Figure 4

Predicted release probability for eight causes of wild birds being admitted to NWBRC for rehabilitation between 2005 and 2024 (n = 4981). Symbols represent estimates coloured and shaped according to the bird group, with error bars representing 95% confidence intervals.

Figure 5

Relationship between ring recovery rate (percentage of recovered individuals after release) and species-specific body mass. Individual circles represent different bird species, with the circle area proportional to the number of ringed birds per species (range = 15–641 individuals). For better display and scale, the species Grey Heron is not shown in the plot (n = 15, body mass = 1500 g, ring recovery rate = 26.7%).