Number of migrants < Threat assessment > Threat assessment for groups

4.2 — Threat assessment

The following sections give a detailed account of the state of knowledge, threat assessment according to international Red Lists, protection status of species by international agreements, and a short outline of major threats for each group. International Red List data from 1996 Baillie & Groombridge 1996) and the "2000 IUCN Red List of Threatened Species"27 (Hilton-Taylor 2000) have been integrated into the database and are compared here. Since 1994, new Red List threat categories are in use, which are more transparent and objective than the older categories and criteria (Annex 6 in Hilton-Taylor 2000). Listing within the categories "Critically Endangered" (CR), "Endangered" (EN), and "Vulnerable" (VU) requires quantitative evaluation, taking into account "population reduction" (criterion A), "extent of occurrence" (B), "critical population size of mature individuals" (C,D) and "probability of extinction in the wild" as calculated by quantitative analysis (E). These criteria give important hints for the nature of a species’ decline, and are contained within the species reports of the GROMS database. To investigate major threat processes in more detail, the IUCN Species Survival Commissions (IUCN-SSC) developed hierarchically structured threat type authority files, to classify the exact nature of threats, such as Habitat loss Agriculture Grazing (Hilton-Taylor 2000, Annex 5). An impressive number of organisations and specialists are involved in the assessment, in particular the IUCN-SSC groups and BirdLife International, which compiles all data on threatened birds (BirdLife International 2000). In total, international Red List assessment is the best and most consistent available data set on threats to biodiversity on a global level. Figure 4.2 summarises the Red List status for mammals and birds listed in the GROMS.

Much more mammals are listed as "Data deficient" (DD) than birds, which reflects their insufficient state of knowledge. The category "Lower Risk/ least concern" (LR/lc) does not exist anymore in the Red List 2000. This category contained species which were assessed, but revealed to be in good conservation status28. The disappearance of this category is a particular problem for migratory species, where certain subspecies and populations can be severely threatened, while the global population might be stable (for example, the ruddy-headed goose, Chloephaga rubidiceps, Figure A2.33). The Red List 2000 does not differentiate between bird subspecies and populations, but lists a considerable number of former bird subspecies as full species. While this is certainly adequate for threat assessment, it leads to considerable compatibility problems with other databases and lists, including Sibley & Monroe (1991, 1993).

For mammals, the Red List 2000 does differentiate between stocks and subspecies, and considerable differences of conservation status within a single species emerged (e.g. gorilla, Figures A2.13-14, and right whales, Figure A2.24). For migratory mammals, trends in changes with respect to the Red List 1996 are small and similar to those observed for all mammals (Hilton-Taylor 2000: Table 2). But there is a noteworthy 13% (38 vs 291) categorised as "Data Deficient", giving testimony of the insufficient state of possibly migratory mammals the Red List total for "Data Deficient" amounts to "only" 5% (240 vs 4700).

In contrast, birds are much better assessed, as shown by the low number of species classifying as "Data Deficient". Around 12% of all bird species are now threatened (1130 of all 9900 bird species), which is only slightly higher than 10% of threatened migratory birds (163 of 1642). But among seabirds, there are 20% of the species threatened. It is therefore necessary to differentiate, and a more detailed account for major groups of migratory birds is given in the respective special section (section 4.3.2, and figure captions of Annex II). Compared to 1996, a considerable increase of 50% (from 82 to 122) for birds classified as "Vulnerable" is notable. Most of these birds were not listed at all in 1996. This is in contrast to the Red List total, where the number of vulnerable birds dropped from 704 to 680, due to a transfer to higher threat status. At present, most threatened migratory birds are still within the lowest category "Vulnerable", but they are now entering the "Road to extinction" (Fitter & Fitter 1987). This means that it is now time to act and avoid that migrants move on to higher threat categories.

Finally, there is the question for the number of extinct migratory species. At least two migratory bird species are definitely extinct: the passenger pigeon (Ectopistes migratorius) (Figure A2.37) and the St. Helena Bulwer’s petrel (Bulweria bifax). Another petrel, the Guadalupe storm petrel (Oceanodroma macrodactyla) is listed as "Critically Endangered" (CR), but last reports are from 1912, and most specialists consider this species to be extinct. Two curlew species are on the brink of extinction: for the American Numenius borealis there have been no clear reports for several years (Figure A2.37), and there are less than 100 slender-billed curlews (Numenius tenuirostris) left (Figure A2.36). Both species were highly numerous, and if they will be saved at all, their population numbers will be a shadow of their former abundance.

Among mammals, there are at least three extinct migrants: the plain’s zebra (Equus quagga), the Caribbean monk seal (Monachus tropicalis) and Steller’s sea-cow (Hydrodamalis gigas). This number would rise to four, if the Japanese sea-lion (Zalophus japonicus) is considered a full species at present, it is red-listed as a subspecies of Zalophus californianus. One could argue if the mentioned taxa were migratory, because we can only speculate about their former migratory behaviour. However, a classification as migrant seems justified, according to museum distribution data and a comparison with extant relatives.

It is now possible to list those migratory species qualifying as "Endangered" according to Red List criteria, and compare this list with CMS appendices. Figure 4.3 shows the summarising statistics, revealing considerable discrepancies. To some extent, these are due to the fact that CMS concentrates on migrants crossing international borders, while several species included in the GROMS complete their migratory cycle within large range states. Evaluation of range state information given by IUCN and/or the GROMS GIS data reveals those migratory species within one range state. The remaining migrants might be candidates for listing on CMS Appendices I and II, as they must definitely be considered as "Endangered" or of "unfavourable conservation status [...] due to the best available evidence", respectively (see Box 4.1). The term "Endangered" as given in Article I, paragraph 1(e) is now interpreted as "facing a very high risk of extinction in the wild in the very near future", and the Conference of Parties decided "to assess the endangered status according to the findings of the 40th meeting of the IUCN council" (Resolution 5.3, CMS 1997). Therefore, the recommendation for further listing is straightforward and presented in the sections analysing the respective animal groups (sections 4.3ff.).

Fig. 4.2:

Number of red-listed migratory mammals and birds. The distinct categories are: EX: Extinct, EW: Extinct in the Wild, CR: Critically Endangered, EN: Endangered, VU: Vulnerable, LR/cd Lower Risk, conservation dependent, LR/nt Lower Risk, near threatened, DD Data deficient, LR/lc Lower Risk, near threatened. Note that the latter category LR/lc is not used any more within the recent 2000 Red List (Hilton-Taylor 2000). Further explanations see text.

Abb. 4.2:

Anzahl der wandernden Säugetiere und Vögel, die auf der internationalen Roten Liste erfaßt sind. Die verschiedenen Kategorien bestehen aus: EX: Ausgestorben, EW: In freier Wildbahn ausgestorben, CR: Vom Aussterben bedroht, EN: Stark gefährdet, VU: Gefährdet, LR/cd: Geringeres Risiko/ abhängig von Erhaltungsmaßnahmen, LR/nt: Arten der Vorwarnliste. Man beachte, daß die ehemalige Kategorie LR/lc in der aktuellen Roten Liste 2000 (Hilton-Taylor 2000) nicht mehr benutzt wird. Weitere Erläuterungen im Text.

Box 4.1:

Interpretation of "unfavourable conservation status" and "endangered" from the Bonn Convention (CMS 1979).

Kasten 4.1:

Erläuterung des " unfavourable conservation status" ("Erhaltungssituation ungünstig") sowie der Kategorie "endangered" ("gefährdet") durch die Bonner Konvention (CMS 1979, BELF 1979, p. 7 ff für deutsche Übersetzung).

Article I


1. For the purpose of this Convention:


b) "Conservation status of a migratory species" means the sum of the influences acting on the migratory species that may affect its long-term distribution and abundance;

c) "Conservation status" will be taken as "favourable" when:

(1) population dynamics data indicate that the migratory species is maintaining itself on a long-term basis as a viable component of its ecosystems;

(2) the range of the migratory species is neither currently being reduced, nor is likely to be reduced, on a long-term basis;

(3) there is, and will be in the foreseeable future sufficient habitat to maintain the population of the migratory species on a long-term basis; and

(4) the distribution and abundance of the migratory species approach historic coverage and levels to the extent that potentially suitable ecosystems exist and to the extent consistent with wise wildlife management;

d) "Conservation status" will be taken as "unfavourable" if any of the conditions set out in sub-paragraph (c) of this paragraph is not met;

e) "Endangered" in relation to a particular migratory species means that the migratory species is in danger of extinction throughout all or a significant portion of its range;

On the other hand, there is a considerable number of migrants listed by CMS which do not classify as "Endangered" according to Red List criteria. This raises the question if the latter are sufficient to diagnose threats to migrants, most of which are difficult to monitor because of their huge ranges including several countries. On a first glance, the global approach of International Red List assessment seems appropriate. However, distortions arise from missing differentiation on an infraspecific level, which is particularly important for migratory species. For example, the migratory South American mainland population of the ruddy-headed goose (Chloephaga rubidiceps) is highly threatened (Gibbons et al. 1998) and listed on both appendices of CMS, but actually not globally red-listed, due to its healthy sedentary population on the Falkland islands/Islas Malvinas (Figure A2.33). Though the populations are not classified by taxonomists as different subspecies, their different migratory behaviour allows a clear differentiation and requires different conservation strategies. In some species, certain migration routes are transmitted behaviourally. An example is the lost Atlantic flyway of the trumpeter swan (Cygnus buccinator), which recently was recovered in a spectacular experiment involving ultra-light glider as a "leading bird" (cf. Bill Sladen and film: "Fly away home"). In particular for birds, the International Red List does not yet make the necessary differentiation between subspecies, and less so populations. Therefore, major threats to important migratory populations might be overlooked.
Several migrants seem to need rather high critical minimal population numbers for their social interactions, because unknown social interactions are vital for these species. Examples are the passenger pigeon (Ectopistes migratorius, Figure A2.37) or the Rocky Mountain locust, which became rapidly extinct after population numbers dropped below a critical level. At present, this seems to be one of the reasons for the population collapse of the social plover (Vanellus gregarius, Figure A2.49).

Fig. 4.3: Threat status and CMS Appendices. Left bars summarise threatened red-listed species (Critically Endangered + Endangered + Vulnerable, see Figure 4.2) according to the International Red List 2000 (Hilton-Taylor 2000) and the Red List 96 Baillie & Groombridge 1996). Right bars indicate number of species listed within CMS Appendices I and II (including whole families). Note that CMS covers only migrants which cross international boundaries, while the GROMS contains species migrating within one range state. On the other hand, CMS covers a considerable number of mammals and birds considered as not threatened by the International Red List 2000. Many of these species are in fact endangered regionally or at a population level. Note that in only five years the number of threatened migrants rose most in birds. Further details see text.

Abb. 4.3: Gefährdungsstatus und Anhänge der Bonner Konvention. Die linken Balken zeigen die gefährdeten (threatened) Arten (Vom Aussterben bedroht + Stark gefährdet + Gefährdet, siehe Abb. 4.2.) nach der Internationalen Roten Liste 2000 (Hilton-Taylor 2000) bzw. der Internationalen Roten Liste 1996 Baillie & Groombridge 1996). Die rechten Balken zeigen die Anzahl der in den Anhängen I & II der Bonner Konvention gelisteten Arten (darunter ganze Familien). Man beachte, daß die Bonner Konvention nur Arten erfaßt, die internationale Grenzen überqueren, während GROMS auch Arten enthält, die innerhalb eines Staates wandern. Auf den Anhängen der Bonner Konvention findet man auch eine erhebliche Anzahl von Säugetieren und Vögeln, die von der Internationalen Roten Liste 2000 nicht als bedroht eingestuft werden. Viele dieser Arten sind jedoch regional oder auf Populationslevel bedroht. Man beachte, daß innerhalb von fünf Jahren die Anzahl bedrohter wandernder Arten innerhalb der Vögel am stärksten angestiegen ist. Weitere Details siehe Text.

In addition to International Red List data, national Red Lists are maintained by most countries. The respective national scientists and organisations are independent from the IUCN Species Specialist groups, and often come up with different results, for several reasons:

In fact, methods and results of threat assessment at a national and international level can differ considerably. Rodríguez et al. (2000) compared four South American Red Lists with the global list, and found that only a quarter of endangered endemic taxa were included in both lists, and that categories were more likely to differ than not, in spite of national adoption of the new criteria.

Finally, one should keep in mind that Red Lists do not provide protection. Though national legislation regulates protection of "endangered species" in most countries, there is no process of "automatic" inclusion of red-listed species. For migratory species in particular, national legislation does not provide the necessary international perspective. This is where international conventions such as CMS come in, which are designed to be backed up by national legal instruments and conservation plans. In addition, they provide an additional assessment of threat: inclusion of species into the respective convention appendices has to be based on a careful examination of conservation status, summarised in extensive proposals (cf. Federal Republic of Germany 1999, for inclusion of sturgeons on Appendix II)29. The same holds for regional agreements such as the Annexes to EC Regulation No. 338/97, the Bern Convention, or agreements of CMS focussing on certain species groups (e.g. EUROBATS: Figure A2.2, African-Eurasian Waterbird agreement – AEWA: Figure A2.26).

Red List data assessment requires considerable time spans, which might lead to unnecessary delay between analysis and a design of efficient conservation plans. In the light of these difficulties, the wider concept of "unfavourable conservation status" as used by CMS as criterion for listing must be considered as an advantage, and it will be a major future task to detect threats to migrants in time. The analysis of regional data sets would be a first step, and examples for regional analysis of extinction, as outlined in section 4.4, could be a starting point.

28 Species accounts for LR/lc are published by BIRDLIFE INTERNATIONAL 2000.
29 Available as full-text documents on the GROMS-CD
Number of migrants < Threat assessment > Threat assessment for groups

This document should be quoted as part of the publication "Riede, K. (2001): The Global Register of Migratory Species ­ Database, GIS Maps and Threat Analysis. Münster (Landwirtschaftsverlag), 400 pp." + CD

 by Klaus Riede