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Edited by: Bruktawit Abdu Mahamued, Kotebe Metropolitan University (KMU), Ethiopia

Reviewed by: Marcelo Bertellotti, CONICET Center for the Study of Marine Systems (CESIMAR), Argentina; Richard Patrick Reading, Independent Researcher,

This article was submitted to Conservation and Restoration Ecology, a section of the journal Frontiers in Ecology and Evolution

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

Birds, especially raptors, play important roles in ecosystems. We examine the International Union for the Conservation of Nature’s (IUCN) Red List to determine which orders of birds have proportionally more or fewer species listed as threatened or declining compared to the Class-wide average. We further examine whether raptors are more threatened or declining than non-raptors and whether the order Accipitriformes is particularly threatened even when excluding Old World vultures – which are especially imperiled. Our results reveal heterogeneity across bird orders in proportions of threatened and declining species, with some orders having greater or lower proportions than the Class-wide proportion. We also show that the proportions of threatened species in each order are correlated with the proportion of declining species. Raptors have both greater proportions of threatened and declining species than non-raptors and Accipitriformes has greater-than-average proportions of threatened and declining species, even if Old World vultures are removed from the analysis. Our results should serve as a framework for discussion of the relative conservation status of bird orders, especially raptors, which are in need of increased conservation attention.

Earth is experiencing a sixth mass extinction – losing species at a rate thousands of times higher than between extinction events (

Such bird declines lessen ecosystem function (

Raptor populations are currently of conservation concern. Over half of raptor species are experiencing population declines and 18% are threatened with extinction (

Old World vultures are especially imperiled, mostly because of intentional and unintentional poisoning (

Here, we examine the IUCN Red List assessments of bird species (

BirdLife International is the Red List Authority for all birds on the IUCN Red List. We therefore obtained data from BirdLife International’s database of Red List assessments (

Following ^{2} test and followed the same simulation methodology above to examine proportions of declining species.

We used logistic regression to examine the proportion of species in each Avian order that is threatened or declining. Under a Bayesian framework, we built a model where species (_{i}∼_{i}) and _{i}) = α_{j}. The model also calculated the average proportion across Class Aves as a derived parameter. We ran the model separately to examine threatened (threatened = 1, non-threatened = 0) and declining (declining = 1; stable, increasing, or unknown = 0). We coded species to be threatened with extinction if they were listed as Vulnerable, Endangered, Critically Endangered, or Extinct in the Wild. We subtracted the proportions of each order from the average across Class Aves to determine which orders have statistically higher or lower than average proportions of threatened or declining species. We considered orders to have proportions different from average if the 95% credible interval of the difference between the proportion of a given order and the average proportion across all Aves excluded zero.

We also built a model that included whether or not a species is a raptor as a binary covariate and estimated the difference between the proportions of threatened or declining species between raptors and non-raptors. We considered there to be a difference between the raptor proportion and the non-raptor proportion if 95% credible interval of the difference excluded zero.

We implemented models using JAGS (

To examine correlations between proportions of threatened and declining species per order, we used the lm() function in R to conduct regressions of posterior draws (

Of the 10,988 species of extant birds recognized by BirdLife International, 1,491 (14%) are threatened with extinction and 5,108 (47%) have declining global populations. Simulations revealed the numbers of threatened (^{2} = 31.95, df = 2, ^{2} = 18.94, df = 2,

Frequency histogram across bird orders of proportion of species that are threatened or declining. The expected distributions are based on simulations.

Of the 36 bird orders, six (17%) had statistically lower proportions of threatened species than average (i.e., the Class-wide proportion) while 12 (33%) had statistically higher proportions than average (^{2} of 0.18 (CRI = 0.03–0.38) and slope of 0.37 (CRI = 0.15–0.61;

Median (points) and 95% CRI (lines) of proportions of threatened and declining species per bird order. Horizontal dashed lines represent the Class-wide proportion (i.e., Average). Orders are more than average (orange) if the 95% CRI of the difference between the order’s proportion and the average is negative, and less than average (blue) if that value is positive. Moving from left to right, orders are ranked by median proportion of threatened species. The parenthetical numbers in the x-axis labels are the number of species per order.

Results of a linear regression between the proportions of threatened and declining species per order. Black line is the median prediction and gray shading is the 95% CRI.

The proportion of Old World vultures that were threatened with extinction was 0.69 (CRI = 0.44–0.89) and that of other Accipitriformes was 0.19 (CRI = 0.14–0.24;

Median (points) and 95% CRI (lines) of proportions of threatened and declining species per group of birds. Horizontal dashed lines represent the Class-wide proportion (i.e., Orders are more than average (orange) if the 95% CRI of the difference between the order’s proportion and the average is negative).

The proportion of raptor species threatened with extinction was 0.19 (CRI = 0.16–0.23) whereas that proportion for non-raptors was 0.13 (CRI = 0.12–0.14;

During the 1990s,

Median of proportions of threatened and declining species per bird order. Orders are more than average (orange) if the 95% CRI of the difference between the order’s proportion and the average is negative, and less than average (blue) if that value is positive.

Both the proportion of raptor species that were threatened and the proportion that were declining were greater than that of non-raptors. Our results therefore support recent work expressing concern over the conservation status of raptors (

Raptor orders generally conformed to the pattern of correlation between the proportions of orders that are threatened and declining. We expected this correlation between threatened and declining proportions because severe population declines are one of the criteria that warrant threatened status (

Unsurprisingly, most orders were statistically average, and some were proportionally more secure. Particularly, the two most speciose orders of birds – Passeriformes (perching birds) and Caprimulgiformes (hummingbirds, nightjars, and allies) – have lower-than-average proportions of threatened and declining species. The only raptor order with any proportion that was statistically less than average was Cariamiformes (seriemas), which consists of two species that are both non-threatened with stable populations. Falconiformes (falcons and caracaras) and Cathartiformes (New World vultures) are raptor orders that had statistically average proportions of threatened and declining species, indicating that these orders are generally equal with most others regarding conservation need.

We analyzed Class Aves mostly at the order level, while particularly examining the evolutionary grade that constitutes raptors (

Our analysis is a framework for discussion of the relative conservation status of bird orders, especially raptors, but caution is needed when using these results to guide conservation action. Because we considered birds with unknown population trends to be non-declining, and many species of birds are poorly monitored, our results should be viewed as conservative with a possible bias against orders with a large percentage of poorly studied species. Indeed, it is possible, perhaps likely, that many of the species with unknown population trends are in decline. Further, similar to the binomial tests performed by

Birds serve well as indicators of biodiversity because they are sensitive to environmental change, widespread, diverse, and relatively easy to monitor (

Publicly available datasets were analyzed in this study. These data can be found here:

CM conceived the study and wrote the first draft. Both authors performed analysis and edited the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

We thank donors to The Peregrine Fund and the M. J. Murdock Charitable Trust for funding. We also appreciate Birdlife International for conducting and sharing Red List assessments.