Introduction

The Pine Warbler (Setophaga pinus Wilson) belongs to the family Parulidae and occurs in eastern North America (^{Howell and Webb 1995}, ^{Rodewald et al. 2020}). The species primarily inhabits open pine and deciduous forests, Oak-scrub-Sand Pine barrens, Banks Pine (Pinus banksiana Lamb) moorland, and similar longleaf pine forests (^{National Audubon Society 2023}). The Pine Warbler breeds in the United States, from eastern Texas and northeastern Arizona to New York and Michigan, and in Canada in Alberta, Manitoba, southern Quebec, and New Brunswick (^{eBird 2023}, ^{De Candido and Allen 2005}, ^{Sibley 2014}, ^{Taylor 2018}, ^{Rodewald et al. 2020}, ^{Hudon et al. 2021}, ^{Naturalista 2023}).

The Pine Warbler migrates to the southeastern United States in winter and returns north in early spring (^{The Cornell Lab 2023}). Long migrations are not common, but sightings from Texas to California reveal the Pine Warbler to be a rare visitor to those states in winter (^{Dunn and Alderfer 2017}, ^{eBird 2023}). The species has occasionally been recorded in the states of Nuevo León, Tamaulipas, and northeastern Coahuila in Mexico (^{Howell and Webb 1995}, ^{Garza Tobón 2020}). The southernmost records of the Pine Warbler are from Costa Rica in Central America, the Dominican Republic and Haiti in the Caribbean, and Colombia in South America (^{Strewe and Navarro 2004}, ^{eBird 2023}, ^{Latta and Sondreal 2023}).

Methods

The present record was obtained in the Cañon de Fernández State Park (25º20'40"N, 103º43'37"W), an area of dry mountain ranges bisected by the Nazas River, in the municipality of Lerdo, in the northeast of the state of Durango. In 2008, Cañon de Fernández Park was declared a RAMSAR site with an area of 17,001 ha, 0.9% of which is the riparian corridor associated with the Nazas River (^{SRNMA 2017}). The altitude varies between 1165 and 1890 m asl with an average annual precipitation of 230 mm (^{SRNMA 2017}). The climate is arid with mean annual temperature of 20°C and a mean annual minimum and maximum of 15°C and 30°C, respectively. The landscape is dominated by desert scrub on the slopes and plains (^{Rzedowski 2006}), with riverine gallery forest and associated aquatic environment (^{RAMSAR 2008}).

The observation was made by AOC during one of the frequent walks in the park between 07:00h. and 12:00h. to observe and photograph the avifauna present in the area. For this purpose, Bushnell Falcon 10 ( 50-mm binoculars and a Nikon COOLPIX P950 digital camera with an 83( optical zoom and a 4.3-357-mm lens focal length are used. The observer walked parallel to the course of the river, pausing to photograph birds.

Results

On 8 January 2023 at 11:42 h (CST), AOC observed a Pine Warbler on a branch of a Montezuma Cypress (Taxodium huegelii C. Lawson) on the bank of the Nazas River in the park (Fig. 1). The temperature at the site was about 12°C, with a clear, sunny sky. The bird was approximately two meters above the ground, between the river and desert scrub. The sighting was brief, at an observation distance of 4-5 m, and two photographs were taken (Fig. 1). In the same tree, a Yellow-rumped Warbler (Setophaga coronata Linneaus) and an American Robin (Turdus migratorius Linneaus) were also observed.

Figure 1 A Pine Warbler (Sethopaga pinus Wilson) perching on a branch of a Montezuma Cypress (Taxodium huegelii C. Lawson) in Cañon de Fernandez State Park, Lerdo, Durango, Mexico. Photographs: Andrés Ortega Chufani, 8 January 2023. 

We identified the Pine Warbler by its conspicuous white bars on the wings and its contrasting dark auricular and the yellow eye ring (Fig. 1B). Subsequently, the identification was ratified in laboratory by contrasting the photographs with the field guide where other characteristics such as yellow underparts, the indistinct olive streaks on sides of the breast, the white belly and undertail coverts, its relatively large bill, and the tail extending beyond the undertail coverts were confirmed (^{Dunn and Alderfer 2017}). The notorious yellow color in the underparts and head, distinguish it from other Setophaga spp. present in the region (winter plumage).

Discussion

Our sighting reported here is the first for the state of Durango and the north-central region of Mexico, considerably expanding the Pine Warbler’s winter distribution in Mexico. The nearest observation to the present record, according to ^{eBird (2023)}, was on 2 February 2020, in the municipality of Monclova, Coahuila de Zaragoza (^{Garza Tobón 2020}), approximately 293 km east of our sighting. ^{Garza Tobón (2020)} mentions seeing a bird perched on flowers of ‘Huizache’, a Sweet Acacia (Vachellia farnesiana Wight and Arn), but the accompanying photographs show the bird perched in a Moctezuma Cypress, similar to the sighting reported here.

Taken together, these two sightings confirm a wider winter range for the species. Whether this is due to a marked change in mature pine forest extent or condition over the last 150 years (^{Pidgeon et al. 2005}) is uncertain, but habitat loss and the effects of climate change on migrant birds is well documented in other species (^{Finch et al. 2017}, ^{Xu et al. 2019}). Furthermore, since migratory behavior is a rapidly evolving trait, species are likely to be adapting to global warming (^{Schaefer et al. 2008}). Alternate environmental stressors or climatic factors may also affect bird migration dynamics, as is the case of forest fires (^{Kittelberger et al. 2022}).

Records such as the one reported here are important as they confirm the regional movements of species in time, as well as the temporal changes in their distributions. In addition, they can identify areas of importance for the conservation of these species. Uncertainty about the occurrence and distribution of most bird species may be due to several factors, including a lack of sightings, limited participation in birdwatching, and a lack of attention to studies of species distributions (^{González Carrasco 2017}). It is thought that if more birdwatchers reported their sightings on citizen science platforms, twice as many species currently considered accidental or winter visitors would be recorded (^{Howell and Webb 1995}, ^{Rivera-López et al. 2016}). Furthermore, the ease of digital platforms for recording bird sightings on a global scale increases our knowledge about species distributions owing to citizen science. Our sighting expands the winter distribution of the Pine Warbler and demonstrates the species’ ability to visit and explore novel habitats in winter, potentially reflecting adaptation to climatic variability and subcontinental changes in landscape structure.