“In this context, the species problem is seen to result from considering descriptions of operational criteria to be descriptions of logically necessary properties. In other words, the species problem results from confusing the concept of species itself with the operations and evidence that are used to put that concept into practice” (de Queiroz 1999: 64).

To this day, biologists have not agreed on a unified species definition to be consistently applied across all organisms in the tree of life (de Queiroz 2007; Stankowski and Ravinet 2021). However, advances have been made in the past two decades, with the proposal of the general lineage species concept (hereafter GLSC), which equates species with “separately evolving metapopulation lineages” (de Queiroz 1998). According to de Queiroz (1998, 1999, 2011), the GLSC can be viewed as a unifying “Darwinian” species concept under which several species delimitation criteria can be accommodated. Importantly, under the GLSC, other existing “species concepts” such as the biological species concept (hereafter BSC) and the phylogenetic species concept (hereafter PSC) are just viewed as alternative thresholds for species recognition under the same speciation continuum, not as opposing definitions of species. Therefore, both the BSC and PSC are equally valid species definitions under the GLSC, although neither of them — in isolation — can claim to have a more accurate definition of species in an evolutionary context (de Queiroz 1998, 1999).

In a recent article, Lima (2022a) discusses the properties of the GLSC (de Queiroz 1998) while also contrasting it with two other main species concepts practiced in ornithology: the BSC and PSC. He then concludes that the Brazilian Ornithological Records Committee (hereafter CBRO) bases its species ranking decisions on a misinterpretation of the GLSC, apparently, in his view, equating it with the PSC (Lima 2022a). This supposed misinterpretation of the GLSC has two major detrimental consequences: (1) misinform the local Brazilian ornithological community about the nature of interspecific limits; and (2) mislead the users of the CBRO checklist “…about the nature of the taxa it contains.” According to Lima (2022a), the root cause of the alleged “pervasive misinterpretation” of the GLSC by the Brazilian ornithological community and the CBRO can be attributed to two publications authored by myself (Aleixo 2007, 2009). These latter publications are in Portuguese and therefore not easily accessible by non-Portuguese speakers, while representing two of the few references on species concepts that are readily available in this language worldwide. While the first publication was a pioneering initiative to propose operational criteria for species recognition supporting taxonomic treatments implemented by the CBRO (Aleixo 2007), the second was a review of the consequences of the adoption of different species concepts in conservation biology (Aleixo 2009). The ideas contained in Aleixo (2009) were some of the many that influenced a major review on “Darwinian shortfalls” in conservation biology (see acknowledgments in Diniz-Filho et al. 2013).

The central flaw in Lima’s (2022a) overall rationale is that contrary to what he repeated several times throughout his commentary, nowhere in Aleixo (2007, 2009) was the GLSC interpreted as synonymous with “monophyly” and “diagnosability.” Instead, “monophyly” and “diagnosability” were merely proposed as operational criteria for recognizing species-level taxa consistent with the GLSC (Aleixo 2007, 2009). Regardless of the species concept adopted, taxonomic committees either elect or adopt operational criteria for validating interspecific limits, i.e., for translating any given species concepts into taxonomic treatments (Isler et al. 1998; Helbig et al. 2002; Tobias et al. 2010). A clear example of this is the convergence between the CBRO (Piacentini et al. 2015; Pacheco et al. 2021) and the International Ornithological Committee’s (hereafter IOC) checklists (Gill et al. 2022) concerning their respective operational criteria for species ranking decisions, despite the fact that they follow different species concepts. Accordingly, the following opening statement can be found on the rationale behind the IOC species delimitation criteria (see https://www.worldbirdnames.org/new/classification/species/): “The IOC World Bird List adopts a modern version of the Biological Species Concept with increased emphasis on monophyletic evolutionary lineages (De Queiroz 1998, 1999; Sangster 2014).” Note that “monophyly” is explicitly mentioned by the IOC statement as a central criterion for species recognition under a BSC that is contained by the unifying GLSC (de Queiroz 1998, 1999). Therefore, the core of Lima’s (2022a) criticism derives from his inability to grasp the differences between the theoretical and operational aspects related to species recognition as practiced by taxonomy committees worldwide. For more on the use of “monophyly” and “reciprocal monophyly” as valid operational criteria for species delimitation under the GLSC, see de Queiroz (2007) and Gill (2014). In fact, de Queiroz (2007: 56) makes this very clear through the following statement: “…attributes such as phenetic distinguishability, reciprocal monophyly, pre- and postzygotic reproductive isolation, and so forth, are all properties that lineages acquire as they separate and diverge from one another and therefore provide evidence of lineage separation and divergence. Because species are conceptualized as (segments of) separately evolving lineages, evidence of lineage separation is evidence for the existence of different species. Thus, the properties in question remain directly relevant to the issue of species delimitation.”

While some taxonomic committees, such as the CBRO, have published their own operational criteria to maximize clarity about their interpretations concerning species limits (Helbig et al. 2002; Navarro-Sigüenza and Peterson 2004; Aleixo 2007), others have not (Remsen et al. 2022), although even in these cases either general references on interspecific diagnosability criteria (Isler et al. 1998) or on the species concept debate (Johnson et al. 1999) are implicitly followed. The reliance of taxonomists on clear-cut operational diagnosability criteria is due to the fact that they are fully aware that in the vast majority of cases, the amount and quality of data available on interspecific limits involving any particular group of taxa are limited, adding a lot of uncertainty concerning species delimitations (Cicero et al. 2021; Winker 2021). This situation leads to the rationale that the more diagnosable two taxa are, the more likely they will belong to distinct species, while the opposite is true if they are less diagnosable from each other (Isler et al. 1998; Tobias et al. 2010, 2021). Very importantly, diagnosability in this operational context is not only actively searched by practitioners of the PSC (see Cracraft 1983), but also by those basing their species-level ranking decisions on the BSC (Isler et al. 1998; Johnson et al. 1999; Watson 2005; Tobias et al. 2010, 2021). This demonstrates that diagnosability is essential for implementing species-level rankings regardless of the species concept followed. Therefore, because “diagnosability” is central to taxonomy practice (i.e., modern taxon descriptions necessarily have to include a “diagnosis” section (ICZN 1999)), and to the work of taxonomy committees, any references to it in Aleixo (2007, 2009) must be interpreted in the context of operational criteria for species delimitations as practiced by taxonomic committees, not as synonymous with species definition under the GLSC.

There is a convoluted logic in Lima’s (2022a) rationale concerning his interpretation of species properties under the GLSC, as exemplified by the following statement: “Under the GLSC…properties (e.g., reproductive isolation, diagnosability, monophyly) emphasized by different species definitions are not defining properties of the species category, but rather properties that species may or may not acquire during the course of their existence (de Queiroz 1998, 2007).” He differentiates between “defining” and “acquired” species properties under the GLSC, but in fact, any of the alluded acquired properties (“…reproductive isolation, diagnosability, monophyly), together, make up for a set of defining species properties encompassed by the GLSC. Hence, contrary to what Lima (2022a) has led his readers believe, “monophyly” is indeed a valid species property, although not the only or the exclusive one under the GLSC. Another important species property accommodated under the GLSC is, for example, reproductive isolation, and this is also fully acknowledged by Aleixo (2007: 302), as shown by the sentence translated as “The proposal of the GLSC is that the ‘limits’ defended by the BSC and PSC, for example, no longer delimit species, but become properties inherent to them along their evolutionary trajectory.” Coalescence theory shows that populations evolve into “metapopulation lineages” through the following sequential stages: polyphyly, paraphyly, and reciprocal monophyly (Avise 2000), with phenotypic diagnosability acquired or not at any of these stages, and reproductive isolation typically being reached at the later stages of this microevolutionary continuum (Stankowski and Ravinet 2021). Hence, reproductive isolation, diagnosability, and monophyly are all non-exclusive yet inherent species properties under the GLSC.

The fact that the GLSC defines “separately evolving metapopulation lineages” as the basis for species definitions (de Queiroz 2007) implies that, while being an evolutionary sound framework for species recognition, its implementation in real-life situations by taxonomists presents a challenge that is nevertheless still largely dependent upon the types, amount, and quality of data available for each case. Tightly linked to this difficulty is the fact that there exist perhaps more different definitions of “metapopulation” than for species, including one that defines metapopulations as a “…group of spatially separated populations of the same species which interact at some level” (https://en.wikipedia.org/wiki/Metapopulation), which is in principle totally disconnected from any kind of species definition (see also Hanski and Gaggiotti 2004). Therefore, in this respect, implementing operational species recognition criteria under the GLSC presents the same (if not even greater) challenges as when doing so under the BSC and PSC, underscoring the need for clear-cut thresholds, as proposed by Aleixo (2007) and practiced by taxonomy committees routinely.

Another false claim by Lima (2022a) is that Aleixo (2007, 2009) have promoted the inaccurate notion that the subspecies category is incompatible with the GLSC. Nowhere in Aleixo (2007, 2009) it is stated that subspecies are incompatible with the GLSC. The usefulness of the subspecies category in an evolutionary framework is fully acknowledged in both publications (Aleixo 2007: 307, 2009: 92), although the operational challenges concerning their delimitation are also discussed specifically in reference to clines, where a recommendation is made not to recognize subspecific level taxa due to the impossibility of a clear-cut diagnoses (Aleixo 2007: 307). The recommendation of discouraging the recognition of species and subspecies across geographic clines is also practiced by other avian taxonomy committees (Helbig et al. 2002) and is due to the difficulty in establishing diagnosability criteria capable of delimiting discrete taxa in these contexts. In fact, geographic clines are hardly compatible with subspecies definitions under the GLSC either, as indicated by de Queiroz (2020: 461): “Conceptualizing subspecies as incompletely separated lineages is strongly at odds with recognizing as subspecies things such as artificial partitions of unitary gene pools based on single characters, arbitrary divisions of gradual clines, and phenotypes that represent individual variation rather than lineage differences—that is, all those questionable uses of the subspecies category that have contributed to its current unpopularity.” Therefore, using this specific reference to subspecies in Aleixo (2007) and interpreting it as a statement synonymous with subspecies being inconsistent with the GLSC is unwarranted. Even worse, Lima (2022a) gives the readers the false impression that, because the CBRO follows the species recognition framework proposed by Aleixo (2007), it does not regard subspecies as taxa worth listing in its published checklists. This is far from reality, as shown by the fact that the vast majority of taxa listed in CBRO’s checklists are indeed subspecies (Piacentini et al. 2015; Pacheco et al. 2021). In fact, the utmost care is taken when citing subspecies so that they fully comply with the ICZN (1999) rules and also with baseline requirements fitting the definition of “incompletely separated lineages (de Queiroz 2020), whenever data is available to support this assessment.

Three examples clearly illustrate how subspecies are actively kept in the CBRO checklists (Piacentini et al. 2015; Pacheco et al. 2021) when recent evidence support their status as evolutionary units, with at least some degree of evolutionary independence from other closely related lineages: Automolus cervicalis badius (Furnariidae; Schultz et al. 2017), Hylexetastes uniformis brigidai (Dendrocolaptidae; Azuaje-Rodríguez et al. 2020), and Myrmoborus lugubris femininus (Thamnophilidae; Thom et al. 2018). In these cases, either extensive gene flow (Thom et al. 2018) or very small degrees of genetic and morphological differentiation (Schultz et al. 2017; Azuaje-Rodríguez et al. 2020) have prevented the CBRO from treating these taxa (at least yet) as full species. The case of Hylexetastes uniformis brigidai is emblematic because it was treated in an earlier version of the CBRO checklist (Piacentini et al. 2015) as a full species but subsequently ranked as a subspecies in its next version (Pacheco et al. 2021), following the results obtained by Azuaje-Rodríguez et al. (2020). In contrast, when particular species or subspecies are shown not to fit the definition of “separately evolving metapopulation lineages” according to recent evidence, they are removed from the CBRO checklist (Pacheco et al. 2021; Piacentini et al. 2015), as illustrated by Celeus grammicus (Picidae) (Sampaio et al. 2018) and Turdus ignobilis cururuensis (Turdidae) (Cerqueira et al. 2016). In sum, contra Lima (2022a), neither Aleixo (2007, 2009) nor the CBRO checklists (Piacentini et al. 2015; Pacheco et al. 2021) deny the utility and operational value of subspecies and their active implementation in the context of the GLSC.

The final claim by Lima (2022a) is that Aleixo (2007, 2009) disseminated the incorrect notion that the GLSC “is somehow interchangeable with or complementary to the Phylogenetic Species Concept (PSC).” Like discussed above, this is a remarkable testimony of Lima’s (2022a) incorrect understanding of the GLSC nexus. In several publications, it is stated over and over again that the GLSC is an unifying species concept under which both the PSC and BSC are fully accommodated as species delimitation criteria rather than species definitions per se (de Queiroz 1998, 1999, 2007, 2011). Therefore, the GLSC is neither “interchangeable” nor “complementary” with the PSC (sensu Cracraft 1983) but instead encapsulates it, as well as the BSC (de Queiroz 1998, 1999, 2007, 2011). Specifically with regard to the relationship between the GLSC and the PSC, de Queiroz (1998: 68) provides the following warning: “The term phylogenetic species concept accurately describes all modern species definitions, which explicitly or implicitly equate species with branches, or branch segments, of phylogenetic trees. The term should not, therefore, be restricted to species definitions developed within the context of Phylogenetic Systematics (Cladistics).” Failing to understand these subtle but rather important conceptual differences may lead to wrong notions about the nature and implementation of the GLSC, such as that put forward by Lima (2022a).

Indeed, what sets the CBRO checklists (Piacentini et al. 2015; Pacheco et al. 2021) apart from other widely cited ones including Brazilian taxa (Gill et al. 2022; Remsen et al. 2022) is exactly the implementation of the GLSC core broad guideline for species definition: “separately evolving metapopulation lineages” (de Queiroz 2005: 6604). Examples abound, but it is worth mentioning herein the following taxa (which I have studied in detail) and that are listed as species in the latest version of the CBRO checklist (Pacheco et al. 2021), but as subspecies in the IOC (Gill et al. 2022) and SACC (Remsen et al. 2022) checklists: Myrmotherula oreni and Sciaphylax pallens (Thamnophilidae), Hylopezus dilutus (Grallariidae), Campylorhamphus gyldenstolpei, Campylorhamphus cardosoi, Dendrocolaptes radiolatus, Dendrocolaptes juruanus, Dendrocolaptes concolor, Dendrocolaptes ridgwayi, Dendrocolaptes retentus, Dendrocolaptes medius (Dendrocolaptidae), and Turdus debilis (Turdidae). Data available for these taxa supported their statuses as “separately evolving metapopulation lineages” (Carneiro et al. 2012; Fernandes et al. 2012; Aleixo et al. 2013; Batista et al. 2013; Miranda et al. 2013; Portes et al. 2013; Cerqueira et al. 2016; Santana et al. 2021). While this evidence has been enough to rank these taxa as full species under the GLSC by the CBRO (Piacentini et al. 2015; Pacheco et al. 2021), when these publications were reviewed by the IOC (Gill et al. 2022) and SACC (Remsen et al. 2022), the consensus was to treat all of them as subspecies. These rulings were mainly motivated not by the failure of those papers to support the taxa analyzed as “separately evolving metapopulation lineages” but instead on two main considerations: first, by the interpretation that those “metapopulations” were not genetically, morphologically, or vocally distinct enough so that their reproductive isolation could be assured, and second, because the sampling design of some of those studies (either in terms of specimens or due to a relatively small number of characters — mostly mitochondrial DNA genes, which represent just one locus in the genome) was regarded as incomplete to rule out the possibility of genetic compatibility with other closely related taxa (see resolutions in the SACC website https://www.museum.lsu.edu/~Remsen/SACCproproster.htm which are also followed by the IOC). Both of these objections are valid considerations under the BSC, but not under the GLSC, which regards the acquisition of reproductive isolation (the BSC threshold for species recognition) only as the crowning stage of the speciation process, which may begin millions of years earlier, as demonstrated for some lineages of Neotropical birds (Cronemberger et al. 2020; Pulido-Santacruz et al. 2018, 2020; Miranda et al. 2021).

Therefore, species ranking decisions made by the CBRO as well as those operational criteria outlined in Aleixo (2007) are in fact guided by the true concept of the GLSC, not by a misinterpretation of it as claimed by Lima (2022a). The proof is the recognition of “separately evolving metapopulation lineages” that may not be necessarily fully reproductively isolated, as independent species as also done by the PSC (see Navarro-Sigüenza and Peterson 2004) but unlike the BSC while at the same time recognizing subspecies as “incompletely separated lineages,” which is not possible under the PSC but totally acceptable under the BSC (Piacentini et al. 2015; Pacheco et al. 2021). Ironically, most of the studies cited above supporting a species status for some taxa in the CBRO (Pacheco et al. 2021) but not in the IOC (Gill et al. 2022) and SACC (Remsen et al. 2022) checklists are true examples of “integrative taxonomy” practice, rightly defended by Lima (2022a) as the “operational counterpart of the GLSC.” Genetic, morphological, and vocal data supported independently evolving “metapopulations” statuses for Myrmotherula oreni (Miranda et al. 2013), Hylopezus dilutus (Carneiro et al. 2012), Campylorhamphus gyldenstolpei, and Campylorhamphus cardosoi (Aleixo et al. 2013; Portes et al. 2013) and genetic and morphological data for Dendrocolaptes radiolatus, D. juruanus, D. concolor, D. ridgwayi, D. retentus, and D. medius (Batista et al. 2013; Santana et al. 2021) and Turdus debilis (Cerqueira et al. 2016). This is also true for Dantas et al. (2021), which is cited by Lima (2022a), but who apparently disregarded it as an example of integrative taxonomy supporting the implementation of the GLSC based on an extensive genetic, morphological, and vocal dataset that took more than 10 years to be amassed, analyzed, and published. The bottom line is that, as can be seen from all the examples mentioned above, not only does the CBRO implement species-level rankings for “separately evolving metapopulation lineages” under an integrative taxonomy approach, but also actively recognizes subspecies in the context of “…incompletely separated lineages,” as advocated by the GLSC (de Queiroz 2020), and in sharp contrast to what Lima (2022a) led his readers believe.

However, like in any other taxonomy committee, members of the CBRO frequently disagree about their interpretation of studies that have supported “separately evolving metapopulation lineages” statuses for some taxa, and a consensus is often achieved not to regard them as species-level taxa. For example, Thom and Aleixo (2015) have proposed based exclusively on molecular data that Thamnophilus aethiops polionotus, T. aethiops atriceps, T. aethiops punctuliger, T. aethiops injunctus, and T. aethiops juruanus (Thamnophilidae) should be treated as independent species given their evolutionary independent status. Nevertheless, most of the CBRO members opted not follow this recommendation, and the committee reached a decision to keep their treatment as subspecies (Piacentini et al. 2015; Pacheco et al. 2021). Similarly, Schultz et al. (2017), Musher and Cracraft (2018), and Azuaje-Rodríguez et al. (2020) found evidence based mainly on genetic data that Hylexetastes stresemanni undulatus (Dendrocolaptidae), Automolus ochrolaemus turdinus, A. ochrolaemus auricularis, A. cervicalis badius, A. infuscatus peruvianus (Furnariidae), Pachyramphus viridis griseigularis, and P. castaneus saturatus (Tityridae) fit the definition of “separately evolving metapopulation lineages” and therefore could be ranked as species under the GLSC. However, again the majority of the CBRO members decided not to treat them as species-level taxa. In all cases above, taxa were kept as subspecies despite evidence of consisting “metapopulations lineages” because of sampling issues (limited number and types of characters and geographic coverage of specimens examined) and also due to nomenclatural issues rendering the implementation of “…taxonomic changes that are considered incomplete or probably temporary due to a lack of information about a particular taxon or a set of taxa that has been subject to recent systematic and/or taxonomic review” (Pacheco et al. 2021). This does not mean that all these taxa are not species under the GLSC, but only that — given evidence at the time when they the committee evaluated these cases — the possibility that they would constitute “…incompletely separated lineages” (sensu de Queiroz 2020) could not be dismissed, at least as interpreted by most voting members.

Like explained in the beginning of this commentary, the translation of any kind of species concept into taxonomic ranking decisions is totally dependent upon the types, amount, and quality of data available for each case. Thus, any checklist should be viewed as a tentative classification based on the most recent available evidence for each taxon it contains and according to the majority’s interpretation of that evidence by committee members. So, reliance on operational criteria, and also on the views of the different taxonomists/committee members about the same dataset being interpreted for operational purposes, are inherent aspects of taxonomy practice and can be extended to the work done by taxonomy committees. A clear example of this is the “Caryothraustes case” (Tonetti et al. 2017) mentioned by Lima (2022a), whereby a morphologically consistent, albeit slightly distinct, taxon (C. canadensis frontalis) was lumped with another (C. canadensis brasiliensis) supposedly only “…because of lack of reciprocal monophyly in a gene tree” (Lima 2022a). It is worth here going through the entire process resulting in the CBRO decision to “lump” brasiliensis and frontalis as a case in point to discuss in more detail how evidence is evaluated, and any changes are implemented in the CBRO checklists.

As discussed above, this particular taxonomic treatment implemented in Pacheco et al. (2021), following the work by Tonetti et al. (2017), derives completely from the types, amount, and quality of data available for this particular case and also from the manner in which the CBRO dealt with this new evidence. In fact, the CBRO never casted a vote on a specific case for synonymizing frontalis into brasiliensis but instead focused its attention in whether or not splitting Caryothraustes canadensis into two species: C. canadensis and C. brasiliensis (i.e., the main focus in Tonetti et al. (2017) as well). This latter split was eventually approved (albeit not unanimously) by the committee, whereas the decision to implement the synonymization of frontalis into brasiliensis in Pacheco et al. (2021) stems from the agreement with the remaining parts of the new treatment proposed by Tonetti et al. (2017), who explicitly based their ranking on the GLSC as implemented in Aleixo (2007). The lack of reciprocal monophyly between frontalis and brasiliensis shown in Tonetti et al. (2017) trees is in fact just one of three other additional factors for not treating them as distinct species or subspecies. First, as explained by Tonetti et al. (2017), “Caryothraustes c. frontalis and C. c. brasiliensis are closely related, with only 0.3% of mitochondrial divergence…On the other hand, individuals of C. canadensis from the Madeira-Tapajós interfluvium show 6.3% of mitochondrial divergence from brasiliensis/frontalis.” Therefore, the genetic divergence separating brasiliensis from frontalis is 21 × smaller than that separating the most divergent lineages within the polytypic C. canadensis, as formerly recognized by the CBRO (Piacentini et al. 2015). Furthermore, the trees in Tonetti et al. (2017) not only show that brasiliensis and frontalis are not reciprocally monophyletic, but also that the level of genetic divergence within each taxon is not different from the level of differentiation between them. This strongly suggests that brasiliensis and frontalis are not differentiated at least in parts of their mitochondrial DNA, in sharp contrast with other taxa formerly grouped under the polytypic C. canadensis, where deep mitochondrial divergences were detected (Tonetti et al. 2017). Second, no consistent vocal differences were detected between brasiliensis and frontalis, although bioacoustical characters failed to distinguish any particular taxon within the polytypic C. canadensis (Tonetti et al. 2017). Third, from a morphological perspective, only the front color differentiated brasiliensis from frontalis, whereas morphometry and other body part colors also failed to distinguish them from each other, as remarked by Tonetti et al. (2017)“…both groups share almost all plumage colors except on the forehead.” Even though a distinct front color could in principle be used as a character supporting frontalis at least as an incompletely differentiated subspecies from brasiliensis under the GLSC or even the BSC, the bulk of the most recent evidence available points to them belonging to a single “metapopulation” lineage with some degree of intraspecific variation (Tonetti et al. 2017; Bocalini et al. 2021). Particularly in the contexts of little to no genetic differentiation, plumage characters deviating from this overall trend might not constitute good predictors of true evolutionary independence between metapopulations (Toews et al. 2016; Mason and Bowie 2020), and the utmost care must be taken in their interpretation. Tonetti et al. (2017) do exactly that through the following statement, thanks to their integrative taxonomy approach: “Further analysis using genomic markers, such as ultraconserved elements… could clarify if the variation on forehead color corresponds with phylogenetic divergence of the two populations putatively isolated by the São Francisco River barrier” (i.e., brasiliensis from frontalis). Ironically, ignoring the multi-character evidence produced by Tonetti et al. (2017), and using just the difference in front color as the sole character diagnosing frontalis as a valid taxon, would be the equivalent of recognizing it as a species under the PSC (due to the sharing of an autapomorphy; Cracraft 1983), but not necessarily under the GLSC (see de Queiroz 2020: 461). Indeed, ultraconserved elements (UCEs) did not recover evidence of genomic differentiation between brasiliensis and frontalis, instead lumping them in the same metapopulation, as opposite to canadensis and the Central American Caryothraustes taxa (Bocalini et al. 2021). This reinforces the notion that the differentiation in front color attributed to frontalis has a narrow geographic and genomic basis rather than resulting from true metapopulation level differentiation. On the other hand, this does not automatically invalidate the recognition of frontalis as a valid subspecies under the GLSC, as rightly pointed out by Lima (2022b), and the CBRO should now — given the combined new evidence put forward by Bocalini et al. (2021) and Lima (2022b) — deliberate for the first time on a specific case dealing with the synonymization between brasiliensis and frontalis. This long paragraph illustrates that the process of translating multi-character evolutionary/taxonomic studies into actual taxonomic treatments is analogous to working on an imperfect puzzle with several missing pieces, not all of them available at the same time, but which, nevertheless, taxonomists and taxonomy committees have to deliver and are expected to do so.

In that sense, it is a shame that the rationale and voting outcomes of the CBRO decisions concerning taxonomic treatments implemented in its checklists (Piacentini et al. 2015; Pacheco et al. 2021) have not yet become publicly available, just like done by Remsen et al. (2022). However, plans already exists for fixing this important issue, and eventually, the deliberation details behind all cases evaluated by the CBRO will be published online. Increasing the transparency about the evaluation and ruling processes practiced by taxonomy committees is essential to strengthen their roles in society and also to preclude any misinterpretations and misconceptions about their work, such as that put forward by Lima (2022a). Furthermore, because of their regulatory nature, taxonomy committees have often been criticized for their rulings and structure (Stopiglia and Raposo 2008; Donegan 2019) and therefore must be open to responsible criticism. They should also evolve, for instance, by taking into account representation issues, ranging from gender, race to regional biases. The recent proposal to unify avian checklists worldwide (Conix et al. 2021; Hobern et al. 2021; Lien et al. 2021; Pyle et al 2021; Thiele et al. 2021; Thomson et al. 2021) is a true testament of the importance of the work being carried out by taxonomy committees, which provide a “summary” of avian diversity that can be easily used by multiple sectors within and beyond academia, including the birding community, nature lovers, journalists, bloggers, stakeholders, and policy-makers. While the advantages of having a single and standardized avian checklist for the entire planet are manifold, implementing this vision will be fraught with difficulties ranging from deciding on a given species concept to be applied consistently throughout all avian lineages based in most cases on fragmentary evidence, to paying the needed attention to inequality issues. It is symptomatic that the worldwide IOC checklist (Gill et al. 2022) board of advisors does not have (at least until 18 December 2022), a single South American representative or even an ornithologists based in that continent, despite the fact that it contains the richest avifauna in the planet. This and other types of inequalities, such as gender bias, are pervasive problems affecting taxonomy committees (including the CBRO) and the taxonomists’ community worldwide, with the highest inequalities in the Global South (Donegan 2019; Salvador et al. 2022; Soares et al. 2022).

If not addressed properly, unfounded commentaries such as the one put forward by Lima (2022a) — which cast serious doubts on the standards upon which the checklists of the CBRO (Piacentini et al. 2015; Pacheco et al. 2021) are produced — may have the unintended effect of amplifying the current representation bias affecting the participation of Latin American ornithologists in global taxonomy initiatives, such as the IOC checklist (Gill et al 2022) and global lists of accepted species (Hobern et al. 2021; Soares et al. 2022). However, like discussed herein, while some of Lima’s (2022a) arguments were simply false, others were misguided by a lack of understanding the two-tier process related to species delimitation in taxonomy, which involves (1) choosing a particular theoretical concept and (2) implementing it based on the evidence available at hand and in contrast with particular well-defined criteria consistent with the species concept being adopted in the first place. The dream of a single avian checklist for the entire planet necessarily passes through the inclusion of the diverse global community of ornithologists in this process, including national/regional taxonomy committees from the Global South. These committees (such as the CBRO) can contribute a lot with their knowledge and perspectives, ranging from uncovering taxa names buried in the “gray literature” (i.e., mainly that not available in English) to unearthing taxonomic studies available only locally as unpublished masters’ or PhD theses and dissertations, but foremost, by offering alternative and complementary views on species delimitation that may be paramount to supporting the recognition of “evolutionary significant units” (ESUs), a cornerstone in conservation biology, irrespective of being called species or subspecies in different avian checklists (Aleixo 2009; Diniz-Filho et al. 2013).