Anim. Migr. 2018; 5: 42-48

Research Article Open Access

Darroch M. Whitaker*, Ian G. Warkentin, Keith A. Hobson, Peter Thomas, Rinchen Boardman Fall and winter movements of Newfoundland Gray- cheeked Thrushes (Catharus minimus minimus) https://doi.org/10.1515/ami-2018-0004 Received July 25, 2018; accepted October 4, 2018 1 Introduction

Abstract: The Newfoundland subspecies of Gray-cheeked The Gray-cheeked (Catharus minimus; Figure 1) is Thrush (Catharus minimus minimus) has declined since a Neotropical migrant songbird that breeds in northern the 1980s and degradation of winter habitat has been boreal forests from Newfoundland to Alaska and across suggested as a contributing stressor. However, the winter the Bering Sea into eastern Siberia. The population range of this subspecies is not well understood, so we breeding on Newfoundland has been described as fitted 29 males with archival GPS tags during summer a distinct subspecies, C. m. minimus, based on size, 2016. Four tagged thrushes were recaptured in summer color, and molecular genetics, while those breeding 2017 and, though all tags had missing locations and from central Labrador west are considered to represent broken antennae, the data retrieved showed that one the “Northern” Gray-cheeked Thrush, C. m. aliciae [1] thrush wintered in the Sierra Nevada de Santa Marta (see [2] for photos and a description of taxonomic and (SNSM) in northern Colombia, one in the nearby Sierra morphological distinctions between subspecies). Though de Perijá in Venezuela, and a third may have settled in once-abundant, the population on Newfoundland has the same region. One tag provided locations until April declined sharply since the 1980s [3]. Little is known about 21 and that thrush was consistently detected within a ~1 the underlying cause(s) of this decline, though both nest ha area through the winter. Locations obtained during predation by red squirrels (Tamiasciurus hudsonicus), fall migration indicated that thrushes travelled to South which were introduced to the island in the 1960s, and America via Central America and possibly by directly loss or degradation of winter habitat have been proposed crossing the Caribbean. Contemporary research indicates as possible stressors [1-3]. However, lack of information that the SNSM is an important migratory stopover for on migratory connectivity and the location of the winter Northern Gray-cheeked Thrushes (C. m. aliciae) but a range for C. m. minimus has been a barrier to evaluating historical report coupled with our observations suggest the latter hypothesis. winter use of the SNSM and adjacent areas in northern The winter range of Gray-cheeked Thrushes spans South America by C. m. minimus, though numbers may be ~2,600 km in northern South America, encompassing lower than during the 1900s. ~4,000,000 km2 (Figure 2; [2]). Within this region the is primarily associated with lowland tropical Keywords: Colombia, migration, migratory connectivity, forests of the northwestern Amazon and Orinoco River PinPoint GPS tag, Venezuela, winter drainages, including southern Venezuela, southeastern Colombia, eastern Ecuador, northeastern Peru and northwestern Brazil, as well as the lower slopes of the *Corresponding author: Darroch M. Whitaker, Parks Canada, Rocky northern Andes in Colombia. Though the broader limits of Harbour, Newfoundland and Labrador A0K 4N0, Canada, E-mail: this winter range are poorly described, they likely include [email protected] northern regions in Colombia and Venezuela as well as Ian G. Warkentin, Environmental Science, Memorial University, Cor- Guyana, Suriname, Trinidad and eastern Panama. Little ner Brook, Newfoundland and Labrador A2H 6P9, Canada Keith A. Hobson, Environment and Climate Change Canada, Saska- is known about the degree of migratory connectivity in toon, Saskatchewan S7N 3H5, Canada this species, though Ungvari-Martin et al. [4] reported that Peter Thomas, Environment and Climate Change Canada, Sackville, individuals wintering at a site in the upper Amazon basin New Brunswick E4L 1G6, Canada of eastern Peru likely bred in northwestern North America Thunder Cape Observatory, Bird Studies Rinchen Boardman, based on stable isotope analyses. George J. Wallace, who Canada, P.O Box 160, 115 Front Street, Port Rowan, Ontario N0E 1M0, Canada first described the distinct appearance of Newfoundland’s

Open Access. © 2018 Darroch M. Whitaker et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution- NonCommercial-NoDerivs 4.0 License. Fall and winter movements of Newfoundland Gray-cheeked Thrushes (Catharus minimus minimus) 43

Figure 1. Newfoundland Gray-cheeked Thrush (Catharus minimus minimus) fitted with a GPS tag (a) note arrow pointing to antenna of GPS tag that is barely visible mid dorsal (b) GPS tag on thrush immediately after attachment and prior to release.

Gray-cheeked Thrushes, carried out an extensive analysis of museum collections and identified eight specimens from South America that he felt were probably from the Newfoundland population [5]. These included the type specimen for the species, which was reported as originating from Bogotá, Colombia, by Frederic de Lafresnaye in 1848, as well as seven individuals collected near Santa Marta on the northeastern coast of Colombia in 1898 and 1899 (p. 391 in [5]; see also [6]). Important details of the migratory behavior of Gray- cheeked Thrushes are also poorly understood. During fall, Gray-cheeked Thrushes from eastern North American breeding sites are known to migrate south through the eastern United States [2]. Most then cross either the Gulf of Mexico or the western portion of the Caribbean to make landfall in the Yucatán Peninsula or further south and west in Central America, after which they continue overland using a coastal Central American route into South America via the Darién in Colombia [7]. However, there is also evidence of flexibility in migratory routes, and a smaller number are thought to travel more directly to South America across the Caribbean, making landfall at Figure 2. Migration and winter locations of four Gray-cheeked sites such as the Sierra Nevada de Santa Marta (SNSM) in Thrushes tracked from a breeding area on Newfoundland, Canada, during fall and winter of 2016 and 2017. Joining lines do not reflect northern Colombia [2, 7]. the actual path. The species’ approximate breeding range is shown We used newly available, lightweight archival Global in green, migration range in yellow, and wintering range in blue Positioning System (GPS) tags to collect information [26]. on migratory movements and wintering areas of 44 D.M. Whitaker, et al.

Newfoundland Gray-cheeked Thrushes. Our primary mixing as we only studied thrushes from one breeding goal was to assess migratory connectivity and identify site, but did calculate the mean pairwise distance between wintering areas of C. m. minimus, with the added hope the wintering sites of individuals and compared this to that locations obtained during migration would offer the breadth of the overall winter range of the species as a insight into the species’ migratory behavior. measure of population spread. For this calculation, range breadth was estimated based on the description provided 2 Methods in [2] (see also Figure 2).

Field work was carried out during June and July of 2016 3 Results and 2017 at a study area in the Long Range Mountains of western Newfoundland that supports a large residual During June and July, 2016, we fitted nine male Gray- breeding population of C. m. minimus (49.8º N 57.3º W; cheeked Thrushes with PinPoint-8 tags and 20 males with see [8]). Thrushes were captured using targeted mist PinPoint-10 tags. PinPoint-8 tags averaged 3.33% of the netting coupled with broadcasts of thrush calls and song mass of the thrushes to which they were fitted (range 2.96- to attract territorial . Captured birds were fitted 3.53%), while PinPoint-10 tags averaged 3.82% of thrush with a uniquely numbered, aluminum federal leg band mass (range 3.12-4.26%). Four of the 29 tagged thrushes on the right leg, and males were also equipped with a were recaptured in June and July of 2017, including three blue plastic band on the left leg and either a PinPoint-8 equipped with PinPoint-8 tags and one with a PinPoint-10 or PinPoint-10 GPS tag (Figures 1 and 3; Lotek Wireless tag. The antenna had been broken off at its base for all Inc., Newmarket, ON, Canada; see [9]); these archival four tags (see Figure 3b), and when downloaded the tags tags collect locations accurate to within a few meters but contained two to seven successful fixes, yielding a total must be recovered when birds return to their breeding of 15 successful fixes as well as seven failed fixes out of territories the following year to download location a maximum of 32 possible; the last successful fix was data. Tags were attached using backpack-style leg loop collected on April 21, 2017 (Table 1). Three tags included harnesses (Figure 3a; [10-12]) made from 0.7 mm diameter fixes obtained in South America and showed that two Stretch Magic silicone cord (Pepperell Braiding Company, thrushes had travelled to the SNSM region of Colombia and Pepperell, MA, USA) joined by melting the ends together one went to a nearby site in Venezuela. However, the last with a soldering iron. Harness lengths averaged 51.8 mm fix for one of the thrushes that went to SNSM was collected (range 50.3-53.7 mm; n = 29), and the average weight of the on October 27, when many thrushes are still migrating, so PinPoint-8 tags (including harnesses) was 1.07 g (range it may not yet have reached its final wintering area. The 1.05-1.09 g; n = 9), while the PinPoint-10 tags averaged 1.23 distance between the two thrushes with winter fixes was g (range 1.11-1.32 g; n = 20). 245 km, while the mean pairwise distance between all PinPoint tags have small batteries and so can three thrushes tracked to South America was 167 km. This only collect a handful of locations over an extended equates to approximately 6.4-9.4% of the breadth of the deployment; we programmed tags to collect locations on winter range of Gray-cheeked Thrushes. One tag included eight pre-selected dates to represent important stages in four fixes collected in the SNSM between December 15, the annual cycle of Gray-cheeked Thrushes (Table 1; [2, 2016 and April 21, 2017, all of which fell within ~110 m of 4, 7, 13]). We presumed that the likelihood of obtaining a one-another at an elevation of ~975 m, and were <20 km successful fix would be highest when birds were roosting, from Santa Marta on the Caribbean coast. so tags were programmed to take fixes at 05:00 h GMT, All four retrieved tags also included fixes collected equivalent to sometime between midnight and 02:00 on migration. On September 25, 2016, one thrush was h local time across the potential migration and winter in northern New Brunswick and another was in coastal range of C. m. minimus. To conserve battery life, tags were Maine, and on October 5, 2016, three of the thrushes were programmed to attempt to obtain a fix for 70 seconds, and in the vicinity of Chesapeake Bay while the fourth was if unsuccessful would shut down until the next scheduled in northern New York (Table 1, Figure 2). On October 27 fix. the four thrushes were scattered at sites surrounding the For studies of breeding populations, Finch et al. [14] Caribbean, with one in western Cuba, one in Honduras, recommend measuring population spread and population one in Panama, and one in northern Colombia. Great- mixing on the wintering grounds as two components of circle distances between pairs of locations collected on 5 migratory connectivity. We could not assess population and 27 October ranged from 1,670 to 3,065 km, indicating Fall and winter movements of Newfoundland Gray-cheeked Thrushes (Catharus minimus minimus) 45

Figure 3. GPS tags used to track Gray-cheeked Thrushes (a) tag with silicone harness ready for deployment (b) four retrieved tags, all of which are missing their antennae.

Table 1: Migration and winter locations of four Gray-cheeked Thrushes tracked from a breeding area on Newfoundland, Canada, during fall and winter of 2016 and 2017. Positions listed as “failed location” indicate that the tag unsuccessfully attempted to collect a location, while “no data” indicates that a location was not attempted, presumably due to battery failure. Date Tag 683 (PinPoint-8) Tag 690 (PinPoint-8) Tag 695 (PinPoint-8) Tag 1207 (PinPoint-10)

September 25, Failed location 43.8045º N x -69.7665º W 47.7256º N x -67.2393º W Failed location 2016 Sagadahoc Co., Maine, USA Restigouche Co., NB, Early fall Canada migration October 5, 2016 36.9116º N x -77.6231º W 38.3793º N x -75.6177º W 43.0967º N x -74.2710º W 38.2224º N x -75.3773º W Mid fall migration Dinwiddie Co., VA, USA Wicomico Co., MD, USA Fulton Co., NY, USA Worcester Co., MD, USA October 27, 2016 22.7437º N x -83.4453º W 15.8036º N x -84.8996º W 9.2681º N x -79.1591º W 10.6918º N x -73.4051º W Late fall migration La Guira N.P., Cuba Río Plátano Biosp. Res., Panamá Prov., Panama Cesar Dept., Colombia Honduras December 15, Failed location 9.2774º N x -72.8324º W 11.0925º N x -74.1007º W Failed location 2016 Sierra de Perijá N.P., Magdalena Dept., Colombia Early winter Venezuela January 22, 2017 Failed location Failed location 11.0928º N x -74.0997º W No data Mid winter Magdalena Dept., Colombia March 1, 2017 No data Failed location 11.0925º N x -74.1002º W No data Late Winter Magdalena Dept., Colombia April 21, 2017 No data No data 11.0925º N x -74.1002º W No data Early spring Magdalena Dept., Colombia migration May 14, 2017 No data No data No data No data Late spring migration 46 D.M. Whitaker, et al. straight-line migration rates of 75.9 to 139.3 km/day that the species winters there ([7, 13, 15, 18]; C. Gómez, (average 127.2 km/day). Universidad de los Andes, Bogotá, Colombia; personal communication). Molecular genetics and stable isotope analyses also indicate that most thrushes migrating 4 Discussion through the SNSM during spring are not from the Newfoundland breeding population and have wintered Our observations add to the growing body of literature farther south, either in the Amazon basin or the Andes [7, 15, 16] which indicates that northeastern Colombia [19]. In contrast, historical observations suggest that Gray- and adjacent portions of Venezuela, but particularly the cheeked Thrushes used to be a regular wintering species SNSM region, are important to Gray-cheeked Thrushes in this same area around Santa Marta [6], hinting that during migration and possibly winter. While our sample the number of Gray-cheeked Thrushes wintering in the size is clearly inadequate to make conclusive statements, region has declined during the last century. The degree museum collections also indicate that the SNSM has to which this may be symptomatic of the decline of the been important for C. m. minimus in the past, as seven Newfoundland subspecies since the 1980s is unknown. of the eight South American specimens attributed to this The locations we identified for birds during subspecies were collected there in 1898-1899; six of these autumn offer insights into the southbound migration thrushes were collected from December to March, when of Gray-cheeked Thrushes. One individual travelled they would have been on winter territories [5]. Indeed, from Newfoundland via northern New Brunswick and the only record suggesting a broader distribution of northeastern New York, suggesting that it may have this subspecies in South America is the type specimen crossed the Gulf of St. Lawrence on a westerly trajectory for the species, which was catalogued as having been (~400 km), rather than taking the much shorter collected ~600 kilometers to the south in the northern southwesterly ocean crossing to Cape Breton, Nova Scotia Andes near Bogotá in 1848 [5]. However, Bangs and (~100 km), as is typically postulated for songbirds leaving Penard [17] suggested that Lafresnaye may not have Newfoundland during fall [20, 21]. This path is similar known the true provenance of this specimen, so it seems to autumn migration routes for Gray-cheeked Thrushes possible that Bogotá was listed either because it was a captured at Tadoussac, Quebec, which were subsequently regional center or because that is where the specimen detected by Motus tracking stations farther south and was acquired from a collector. Our observations also hint east along the St. Lawrence River Valley [22]. Recent that migratory connectivity, as measured by population research has demonstrated that this species is capable of spread of wintering individuals, may be relatively high for making ocean crossings in excess of 2,500 km [13, 18]. Our this subspecies. Finch et al. [14] reported that migratory observations hint that for smaller water bodies the species connectivity is generally low for migratory land birds, may not simply choose the shortest possible crossing, and that the mean pairwise distance for individuals from but rather may select routes reflecting other migratory a single breeding population wintering in South America decisions or perhaps links to historical pathways. was ~960 km, equivalent to ≥20% of the breadth of their Gómez et al. [7] suggested that thrushes observed in winter range. In contrast, the observed pairwise spread for the SNSM during fall migration have made landfall after a the Newfoundland Gray-cheeked Thrushes we tracked to direct crossing of the Caribbean, and postulated that the South America was 167-245 km, or ~6.4-9.4% of the breadth Darién (i.e., a Central American route) and SNSM represent of the species’ winter range. Finch et al. [14] proposed that alternate arrival points for thrushes travelling to South isolation by historic land and sea barriers can lead to higher America. However, it seems likely that one or possibly migratory connectivity for a population; consistent with both of the thrushes that we located in Central America on this, molecular genetics analysis suggests that isolation October 27th travelled overland (possibly with some flight in an Atlantic shelf refugium during the Pleistocene may segments across the Caribbean) to enter South America have led to divergence between C. m. minimus and Gray- via the Darién, and then turned back to the northeast to cheeked Thrushes (C. m. aliciae) breeding in mainland reach wintering sites in northern South America (again, North America [1]. possibly with some flight over the Caribbean). Thus, our That one thrush was consistently detected through data suggest that some thrushes that winter in northern the winter within an ~1 ha area just a few kilometers South America travel there via Central America, which from Santa Marta, Colombia, is surprising, as seven years would constitute a longer route than travel directly of contemporary research on migrating Gray-cheeked from the southeastern United States (perhaps Florida) Thrushes at a nearby study site yielded no evidence to SNSM. This finding concurs with indications that Fall and winter movements of Newfoundland Gray-cheeked Thrushes (Catharus minimus minimus) 47 higher numbers of Gray-cheeked Thrushes appear to the SNSM, and research there has demonstrated that, pass through the Darién in fall [7]. It is not clear whether compared to native forest, these shade coffee plantations the other two thrushes we tracked also traveled through offer limited food (i.e. fruit) and are little used by Gray- Central America, or if they instead crossed the Caribbean cheeked Thrushes during migration [13, 16, 24]. Thus the more directly. Averaged minimum daily travel rates for our amount and quality of habitat available to thrushes may four birds over 22 days in October was 127.2 km/day, which be limited (see also [23]). Further, the SNSM and Darién are is comparable to the values determined from Motus tower two of the largest expanses of forest in northern Colombia, detections for five birds initially tagged in southeastern but between them is a broad area that has largely been Quebec and tracked to Latin America. Values calculated converted to agriculture [7]. As a consequence, thrushes based on final detection in the tagging region to initial migrating to northern South America via the Darién detection in Latin America ranged from 98.0 km/day over are potentially crossing an ~400 km-wide expanse of 49 days to 130.6 km/day over 33 days with an overall mean degraded habitat to move into the SNSM region. of 121.9 km/day for birds originating in Quebec [22]. Our observations do not address the hypothesis This study also provided an opportunity to assess the that red squirrel nest predation may also be adversely performance of the PinPoint GPS tags we employed. The affecting the population of Gray-cheeked Thrushes tags logged precise locations that, for example, allowed breeding on Newfoundland [1-3]. However, the occurrence us to identify specific protected areas that the thrushes of individuals in the SNSM region of Colombia, where used thousands of kilometers from our study area, and habitat has apparently been heavily altered, hints that also to identify a stand of trees used for roosting over a habitat degradation and loss in wintering areas may be period of more than four months by one individual (Table a contributing factor to the decline of C. m. minimus. To 1). Follow-up study could enable us to identify specific better understand the effect of habitat degradation in habitats used throughout the nonbreeding period (see South America on this subspecies, additional data on the [9]). However, the reliability of the tags was problematic, location of wintering areas and the degree of migratory as on average they yielded less than half of the maximum connectivity are needed. While further use of GPS tags possible number of fixes. This was most likely because may be useful in this regard once issues related to tag the antennae had been broken off all four recovered tags, robustness and performance are addressed, we suggest indicating that a more robust design is needed to ensure that alternative or complementary research tools to retention and functioning of the antenna. All tags also explore migratory connectivity also should be considered stopped trying to collect locations before the end of their [e.g., 23, 25]. deployment schedule – one as early as January 22 (~7 months after deployment) – indicating that battery life is Acknowledgements: Research was supported by the a limiting factor for overwinter deployments. Centre for Forest Science and Innovation (Government Though it is clear that more data are needed, our of Newfoundland and Labrador, Department of Natural observations combined with historical records suggest Resources), the Natural Sciences and Engineering that a region of northern South America near the Research Council of Canada, Parks Canada, and the border between Colombia and Venezuela is important Canadian Wildlife Service. Kevin Kardynal, Jenna for Newfoundland Gray-cheeked Thrushes. This area McDermott, and Bruce Rodrigues assisted with various has experienced extensive habitat modification (e.g., aspects of study development and field work. Research deforestation; conversion to shade coffee), so our was conducted under banding permits from the Canadian observations are consistent with the hypothesis that Wildlife Service as well as scientific permits from the degradation or loss of stopover and/or winter habitat may NL-Wildlife Division, NL-Parks and Natural Areas Division, be a stressor affecting C. m. minimus. Similarly, Kramer and the Institutional Care Committee of Memorial et al. [23] found that declining breeding populations of University of Newfoundland (16-15-IW). Golden-winged Warbler (Vermivora chrysoptera) had high migratory connectivity with a restricted wintering area Author contributions: DW, IW, KH and PT contributed in the same region of northern South America, whereas to the development of the project; RB led the data breeding populations that wintered elsewhere have collection. DW and IW produced the initial drafts and all remained stable. There has been extensive deforestation authors contributed to interpretation and writing of the and conversion of premontane forest to shade coffee in manuscript. 48 D.M. Whitaker, et al.

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