Retrospective study on admission trends of Californian hummingbirds found in urban habitats (1991-2016)

Pranav S Pandit; Ruta R Bandivadekar; Christine K Johnson; Nicole Mikoni; Michelle Mah; Guthrum Purdin; Elaine Ibarra; Duane Tom; Allison Daugherty; Max W Lipman; Krystal Woo; Lisa A Tell

doi:10.7717/peerj.11131

Retrospective study on admission trends of Californian hummingbirds found in urban habitats (1991-2016)

PeerJ. 2021 Apr 13:9:e11131. doi: 10.7717/peerj.11131. eCollection 2021.

Authors

Pranav S Pandit^#¹, Ruta R Bandivadekar^#², Christine K Johnson¹, Nicole Mikoni², Michelle Mah³, Guthrum Purdin⁴, Elaine Ibarra^{5

6}, Duane Tom⁷, Allison Daugherty⁴, Max W Lipman⁴, Krystal Woo⁴, Lisa A Tell²

Affiliations

¹ EpiCenter for Disease Dynamics, One Health Institute, School of Veterinary Medicine, University of California, Davis, Davis, CA, USA.
² Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, Davis, CA, USA.
³ Department of Wildlife Fish and Conservation Biology, University of California, Davis, Davis, CA, USA.
⁴ Lindsay Wildlife Experience, Walnut Creek, CA, USA.
⁵ Santa Barbara Wildlife Care Network, Santa Barbara, CA, USA.
⁶ Wild Neighbors Database Project, Middletown, Middletown, CA, USA.
⁷ LA Wild, Los Angeles, CA, USA.

^# Contributed equally.

Abstract

Background: Hummingbirds are frequently presented to California wildlife rehabilitation centers for medical care, accounting for approximately 5% of overall admissions. Age, sex, and reason for admission could impact hummingbird survivability, therefore identification of these factors could help maximize rehabilitation efforts.

Methods: Mixed-effects logistic regression models were used to identify specific threats to the survival of 6908 hummingbirds (1645 nestlings and 5263 non-nestlings) consisting of five species (Calypte anna, Calypte costa, Selasphorus rufus, Selasphorus sasin, Archilochus alexandri), found in urban settings, and admitted to California wildlife rehabilitation centers over 26 years.

Results: In total, 36% of birds survived and were transferred to flight cage facilities for further rehabilitation and/or release. Nestlings were more likely to be transferred and/or released compared to adult hummingbirds. After accounting for age, birds rescued in spring and summer were twice as likely to be released compared to birds rescued in the fall. A high number of nestlings were presented to the rehabilitation centers during spring, which coincides with the nesting season for hummingbirds in California, with the lowest number of nestlings presented in fall. Reasons for presentation to rehabilitation centers included several anthropogenic factors such as window collisions (9.6%) and interactions with domesticated animals (12.9%). Survival odds were lower if a hummingbird was rescued in a "torpor-like state" and were higher if rescued for "nest-related" reasons. Evaluation of treatment regimens administered at wildlife rehabilitation centers identified supportive care, including providing commercial nutrient-rich nectar plus solution, to significantly increase hummingbird survivability.

Discussion: Our results provide evidence of threats to hummingbirds in urban habitats, based on reasons for rescue and presentation to rehabilitation centers. Reasons for hummingbird admissions to three California wildlife rehabilitation centers were anthropogenic in nature (i.e., being associated with domestic animals, window collisions, and found inside a man-made structure) and constituted 25% of total admissions. There was a clear indication that supportive care, such as feeding a commercial nectar solution, and medical treatment significantly increased the odds of survival for rescued hummingbirds.

Keywords: Anthropogenic threats; Archilochus alexandri; California; Calypte anna; Calypte costa; Selasphorus rufus; Selasphorus sasin; Wildlife rehabilitation; Wildlife rescue.

Grants and funding

This study was funded by the support from The Hunter-Jelks Foundation, The James Kralik Charitable Fund, Dr. and Mrs. Grant Patrick, and Dr. and Mrs. Terry Roelofs. There was no additional external funding received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.