Migration ecology of western gray catbirds

Abstract

Background For many songbirds in North America, we lack movement details about the full annual cycle, notably outside the breeding season. Understanding how populations are linked spatially between breeding and overwintering periods (migratory connectivity) is crucial to songbird conservation and management. We assessed migratory connectivity for 2 breeding populations of Gray Catbirds (Dumetella carolinensis) west of and within the Rocky Mountains by determining migration routes, stopover sites, and overwintering locations. Additionally, we compared apparent annual survivorship for both populations. Methods We deployed 39 archival light-level geolocators and 21 Global Positioning System (GPS) tags on catbirds in the South Okanagan Valley, British Columbia, Canada, and 32 geolocators and 52 GPS tags in the Bitterroot River Valley, Montana, USA. These devices allowed us to determine migration routes, stopover sites, overwintering locations, and migratory connectivity. Migratory connectivity was quantified using Mantel’s correlation. We used mark-recapture of colour banded catbirds in both sites to estimate apparent annual survivorship. Results We retrieved 6 geolocators and 19 GPS tags with usable data. Gray Catbirds from both populations passed through the Rocky Mountains eastward before heading south towards their overwintering locations in northeastern Mexico and Texas. Stopover sites during fall migration occurred primarily in Montana, Kansas, Oklahoma, and Arkansas. Overwintering locations spanned Texas and 5 states in northeastern Mexico. Individual catbirds used up to 4 distinct sites during the overwintering period. Catbirds separated by almost 500 km during the breeding season overlapped during the non-breeding season, suggesting weak migratory connectivity among western populations (Mantel’s correlation = 0.013, P-value = 0.41). Catbird apparent annual survivorship estimates were higher in British Columbia (0.61 ± 0.06 females; 0.64 ± 0.05 males) than in Montana (0.34 ± 0.05 females; 0.43 ± 0.04 males), though the main driver of these differences remain unclear. Conclusions Our results provide high precision geographic details during the breeding, migration, and overwintering phases of the annual cycle for western Gray Catbirds. Notably, we found that western catbirds followed the Central Flyway as opposed to the Pacific Flyway. We document that catbirds used multiple sites over winter, contrary to the popular belief that this phase of the annual cycle is stationary for most songbirds.

Demographic responses to climate‐driven variation in habitat quality across the annual cycle of a migratory bird species

“…Our tracking data suggested that within‐season movements outside of the breeding season may be common for black‐headed grosbeaks that breed in California, particularly during the molting period, although larger movements near seasonal transitions may more accurately be considered to be protracted migrations than within‐season movements. Support for non‐breeding season movements has been reported for other migratory landbird species (Cormier et al, 2013 ; Mancuso et al, 2021 ; Ruiz‐Gutierrez et al, 2016 ; Stutchbury et al, 2016 ), and flexibility to move to new sites within seasons may be a critical adaptation for tracking uncertain environmental conditions. Both yearling males that showed within‐molting season movements initially settled in habitats that were less green than those settled in by the older adults.…”

“…Rapid advances in tracking technology have allowed for identification of these connections for a growing list of migratory animal species (McKinnon et al, 2013 ; Ruegg et al, 2014 ; Rushing et al, 2014 ). However, the value of this information for conservation is relatively limited without also identifying key environmental stressors at different points of the life cycle to better understand the consequences of migratory connections for population dynamics (Mancuso et al, 2021 ; Rushing, Ryder, & Marra 2016 ; Saracco & Rubenstein, 2020 ; Wilson et al, 2018 ).…”

Migration and non-breeding ecology of the Yellow-breasted Chat Icteria virens

“…In BC, California, and Nayarit, birds were also given three colour bands to aid in resighting. One right outer rectrix (R6) was collected for genetic analyses (and corticosterone, Mancuso et al 2021 , pending). One right inner secondary feather (S4–S6) was collected for hydrogen stable isotope analyses, except in California where no secondaries were collected, but instead, two outer rectrices were taken.…”

“…Tags were scheduled to take the fix at 16:00 or 17:00 GMT (9:00 or 10:00 PDT) where birds should be awake and active. We tested the same type of GPS tags for another study before deployment at a stationary location in BC and found that accuracy was within a few meters for many points, and 90% of points were within 100 m (Mancuso et al 2021 ). According to the manufacturer, the lowest levels of accuracy (which ought to be removed) are 300 m (Lotek Wireless Inc. 2018 ).…”

No “carry-over” effects of tracking devices on return rate and parameters determining reproductive success in once and repeatedly tagged common swifts (Apus apus), a long-distance migratory bird

“…Thanks to tracking devices such as light level-geolocators (hereafter "geolocators"), GPS loggers or radio transmitter, we gained knowledge about migration behaviour [4], like timing of migration, migration tracks, locations of overwintering areas and the time they spend in each area [i.e. [6][7][8]. All this information contributes to a better understanding of life-history strategies in long-distance migratory bird species [9,10].…”