Status Assessment 2025 - Roseate Tern

Confidence

High

Background Information

• Year added to OSPAR List: 2003 (OSPAR, 2008)
• The original evaluation of Roseate tern against the Texel-Faial criteria referred to regional importance, rarity, sensitivity and decline, with information also provided on threat
• Last status assessment: 2009. OSPAR (2009) assessment was conducted shortly after the species case report. Although the species was assessed as no longer in catastrophic decline, it had been undoubtedly rare and at risk because of restricted breeding range. The population was fluctuating, and had not recovered from former, severe declines.

Geographical Range and Distribution

The breeding distribution of Roseate tern experienced little change since the 2009 assessment. The most notable was found in Brittany (France), after the returning of birds to a historic colony of the Bay of Biscay and Iberian Coast (Region IV) in 2011, following the collapse of other Brittany colonies located in the Celtic Seas (Region III). Other than that, the species is still confined to a few colonies in the Greater North Sea (Region II), Region III and the Wider Atlantic (Region V), with a noticeable shrink of Azorean colonies before the 2009 assessment (Figure 1). All OSPAR populations winter outside of the OSPAR area, mostly in West Africa and Brazil.

Method of assessment: 2a – sources: Cabot (1996), Piec & Dunn (2021), Quemmerais-Amice (2011).

Population/Abundance

Trends in relative abundance (Figure 2) show a recovery in breeding numbers of Roseate tern in Regions II and III since 2008 (Table 1) although yet not enough to compensate the substantial declines since the baseline from 1960-1969, which had already been identified when this species was added to the T&D list and is documented in the background document (OSPAR, 2009). Conversely, in the OSPAR Quality Status Report 2023 (QSR 2023) the status of Roseate tern was assessed as good in Region II by the marine bird abundance common indicator (OSPAR, 2023; Dierschke, 2022). Differences between the QSR 2023 assessment and the current one are most related with the period set as baseline (more details at the additional information of Assessment methods section). The French colony located in Ile aux Moutons (Brittany, Region IV) was recently recolonised with a population of 30 to 49 breeding pairs (2015-2019; Table 1). In Region V, the population is showing great fluctuations in terms of abundance since the baseline from 1984-1993.

Table 1: Number of breeding pairs and relative breeding abundance (a proportion of the baseline in 1960-1969 for the Greater North Sea, the Celtic Sear and the Bay of Biscay and Iberian Coast or 1984-1993 for Wider Atlantic, set at 1.0) of Roseate terns in each OSPAR Region. Trend between last assessment (2008) and current population size (2020 for Regions II, III and V, 2024 for Region IV) is also given for each region, as increasing (↑) or stable (←→).

	Baseline	2008		2022 or 2024		Trend
OSPAR Region	No. pairs	No. pairs	Relative abundance	No. pairs	Relative abundance	2008-2020
II	226-604	72-99	0.21	178-131	0.30	↑
III	2736-3959	67-1787	0.27	2157	0.55	↑
IV	10-70	0-0		17-20		↑
V	379-1188	308-1100	0.94	538-1068	0.92	←→

Figure 2 (a, b, c): Trends in relative breeding abundance of Roseate tern in each of OSPAR Regions II and III during the period 1960-2020, and Region V, during the period 1984–2019. The baseline is where relative abundance = 1.0. The red dotted line indicates the lower assessment value of 0.7; the black dashed line indicates the upper assessment value of 1.3

Method of assessment: 3a – sources: Cabot, 1996; JNCC, 2021; MacLeod-Nolan, 2023; Mitchellet al., 2000; OSPAR, 2009; Piec, 2021; Piec & Dunn, 2021; Quemmerais-Amice, 2011.

Condition

The condition of breeding populations of Roseate tern was assessed using the common indicator of marine bird breeding productivity (B3) in combination with data obtained from the literature. The expected annual population growth rates based on demographic data of Roseate tern in OSPAR Regions II and III were above the threshold values (Figure 3). Despite the relatively stable trend of the single colony located in OSPAR Region IV, it showed low breeding productivity (MacLeod-Nolan, 2023). In Region V, productivity in the Azores was infrequently monitored during the last decades, preventing any assessment.

Figure 3: Expected annual population growth rates in OSPAR Regions II and III. The colour-coded background shows the threshold values; values in the green zone indicate the threshold is achieved, whereas values in the other zones are below and indicate the threshold has been failed. For illustration, the figure also shows a breakdown for the corresponding IUCN red list categories of Vulnerable (VU), Endangered (EN) and Critically Endangered (CR)

Method of assessment: 3a, b and  d – sources: Frederiksen et al., 2022; MacLeod-Nolan, 2023; OSPAR, 2023; Piec, 2021.

Threats and Impacts

Predation and displacement by large gulls, native mammals and non-indigenous species are still considered high level threats in most of OSPAR Regions. However, some management examples proved to be effective towards tern protection. Additionally, the trapping of adult terns in wintering areas (mostly Ghana) still occurs but at lower levels.

Medium-level threats identified in the previous assessment remain, including predation by bird species, other than large gulls, habitat damage due to uncontrolled access of people in breeding grounds, egg collecting, climate-driven events, food shortages, development of offshore windfarms, overfishing and climate change impacts on cold water upwelling systems. 

A severe mortality event caused by a Highly Pathogenic Avian Influenza (HPAI) outbreak resulted in a reduction of 21% of breeding pairs from 2022 to 2023 in Coquet Island (Tremlett et al., 2024). Showing the high-level impact that such diseases might have.

Measures that address key pressures from human activities or conserve the species/habitat

Roseate tern is legally protected in all countries within the OSPAR area where the species occurs. Additionally, all breeding colonies are located within Special Protection Areas (SPA),  across France (3), Ireland (2), Portugal (12) and the UK (3), some of them also including foraging areas. The OSPAR’s Regional Action Plan for Marine Birds in the North-East Atlantic (2024-2030) was published in 2024. The International Species Action Plan for the Conservation of the Roseate tern in the East Atlantic (2021-2030) was published in 2021 (Piec & Dunn 2021). Portugal (Madeira) published a regional action plan for 14 seabird species, including Roseate tern (SPNM, 2015). All these measures followed the OSPAR Recommendation 2011/06, namely 3.1 and 3.2.

Conclusion (including management considerations)

Since the first status assessment in 2009, there have been considerable improvements towards the conservation of Roseate tern, although intensive management measures at key colonies and increased protection in crucial wintering grounds remain necessary.

Most of the colonies in North-West Europe, and some in Azores, are actively managed for the provision of nesting habitat, control of predation and disturbance, biosecurity measures and monitoring. A recovery at the Irish and UK colonies has been noticed over the last 3 decades, although the size of those populations is far below the historic numbers found during the 1960’s. The situation in France and in Azores is much more variable as the level of management of colonies has been less robust. Consequently, colonies tend to relocate more frequently, depending on the local conditions each year.

Predation and displacement by large gulls, native mammals and non-indigenous species are still considered the most problematic threats in the OSPAR area, reducing breeding productivity, which may enhance the negative effect of the lower adult survival rates found at certain sites.

Although beyond the OSPAR maritime area, tern trapping continues in wintering grounds (in west Africa) which may limit the recovery of Roseate tern. Communication, raising awareness and coordination with other conventions (e.g. AEWA) and/or organizations would be desirable.

The condition of the population breeding in Region V, as well as their wintering areas are still poorly understood. Moreover, threats in the known wintering grounds and migration routes used by all OSPAR populations have been largely neglected. Changes at those locations could have serious implications to Roseate terns. 

A re-assessment could be conducted over a long-term cycle, i.e. 10 year, based on the anticipated availability of evidence and expected development of the populations.

Knowledge Gaps

Lack of standardisation and sufficient quality of monitoring data to inform metapopulation management is most apparent in OSPAR Region V. Where possible, at least basic demographic parameters should be recorded, in addition to the number of nesting pairs, such as clutch size and productivity.

The lack of knowledge on the current conditions of staging sites within Region III, on the threats to coastal and marine environments induced by climate change and human disturbance, and on the current conditions of coastal wintering sites in West Africa and North East South America are among the top priority limitations which need to be addressed.

Sheet reference:

BDC2025/Roseate_tern