Evidence for longitudinal migration by a “sedentary” Brazilian flycatcher, the Ash-throated Casiornis

Abstract

The digitalization of museum collections and concurrent increase in citizen‐science initiatives is ushering in an era of unprecedented availability of primary biodiversity data. These changes permit a reappraisal of phenological patterns of tropical species. I examined spatio‐temporal variation in the distribution patterns of an ostensibly sedentary endemic Brazilian flycatcher, the Ash‐throated Casiornis (Casiornis fuscus), using both specimen data from museums and sighting records and rich media data from citizen‐science initiatives. I found compelling evidence for partial intratropical longitudinal migration to Amazonia and the Cerrado biomes from the species’ core range in the semi‐desert Caatinga biome and adjacent ecotones. These records from outside of the Caatinga were distributed during the height of the dry season from April to October, although the Caatinga is not entirely vacated at this time. This pattern of partial migration leads to a doubling of the distributional range of Ash‐throated Casiornises and strongly suggests that the species is a breeding near‐endemic of the Caatinga biome. This pattern was potentially previously not apparent because of significant biases in specimen collection between biomes, giving a false sense of abundance in the Brazilian Amazon.

An overview of migratory birds in Brazil

“…As stated by Sick (1997), it seems to be present in the north of its distribution only as a visitor during winter. This statement was recently confirmed and deepened a space-time analysis of historic records of museum specimens, field observations and digital vouchers at WikiAves and e-bird (Lees, 2016). In this analysis, a migratory pattern from part of the Caatinga and adjacent ecotones was identified, where records are centered in the period between December and March, expanding west to northern Cerrado and eastern Amazon between June and September.…”

“…In this analysis, a migratory pattern from part of the Caatinga and adjacent ecotones was identified, where records are centered in the period between December and March, expanding west to northern Cerrado and eastern Amazon between June and September. Although it can be recorded throughout the year in the Caatinga, where it also breeds, as corroborated by banding data (SNA, 2016), its occurrence in the Amazon is restricted to the period between April and October, when they use mainly open formations and young secondary forests as wintering areas (Lees, 2016).…”

Assessing bird migrations

“…Nevertheless, any classification using this typology should not be considered definitive and should be updated constantly as more is discovered about species' movements. For instance, there are many examples of migratory movements detected in species long considered resident, including the Little wood-rail Aramides mangle (Marcondes et al 2014), the Rufous-thighed kite Harpagus diodon (Lees & Martin 2015) and the Ash-throated casiornis Casiornis fuscus (Lees 2016…”

“…Some of the nomadic, undefined and partial migrants could, in fact, be performing movements more regular than we think, and some of the residents could actually be migrants or partial migrants. There is a steady stream of studies revisiting migratory status in species formerly thought to be sedentary, such as the Little wood-rail Aramides mangle (Marcondes et al 2014), the Rufous-thighed kite Harpagus diodon (Lees & Martin 2015) and the Ash-throated casiornis Casiornis fuscus (Lees 2016). Additionally, in some cases species are known to perform some type of cyclical seasonal movements, but little is known about their spatial pattern, such as the Slaty elaenia Elaenia strepera (Marantz & Remsen 2013).…”

Dinâmica de populações e comunidades de borboletas e aves ao longo do tempo

“…A concepção clássica de que aves tropicais residentes, especialmente aves florestais, seriam sedentárias (i.e., não-migratórias) vêm sendo desafiada por estudos de campo (Loiselle & Blake 1991, Levey 1994, pelo uso de tecnologias de rastreamento (Jahn et al 2013, Cueto et al 2015, Guaraldo et al 2016) e por grandes bases de dados de ocorrência abastecidas por cidadãos (e.g., Wikiaves, E-bird; Lees & Martin 2015). Estes estudos vêm revelando que algumas espécies neotropicais tradicionalmente tidas como sedentárias realizam movimentos migratórios anuais (e.g., Lees & Martin 2015, Lees 2016. Assim, a mistura complexa de espécies migratórias e sedentárias em florestas tropicais pode gerar mudanças anuais na composição de espécies (Loiselle & Blake 1992, Faaborg et al 2010.…”