Survival estimates of Northern GannetsMorus bassanusin Alderney: big data but low confidence

Abstract

Capsule: There has been a linear increase in the survival rates for both adult and juvenile Northern Gannets Morus bassanus breeding on Alderney in the English Channel. However, given large confidence intervals, improved monitoring is required to better evaluate threats to this population. Aims: To estimate the age-specific survival and reporting rate from an internationally important population of Northern Gannets M. bassanus breeding at one of the southernmost colonies for this species. Methods: We use 28 years of ringing and recovery data in order to estimate age-specific survival and reporting rates. Results: Adult and juvenile survival rates differ, and both survival and reporting rates are considerably lower in first-year birds than older birds. Additionally there is an increasing linear trend in survival rates over time, and a decreasing trend in reporting rates. Conclusion: Threats to Gannets from anthropogenic disturbance are likely to be age and population specific. While these rates point towards continued growth of this population, the confidence intervals around our estimates are large, highlighting the need for improved resighting efforts in long-term studies of this nature.

A new method for quantifying redistribution of seabirds within operational offshore wind farms finds no evidence of within-wind farm displacement

“…the following breeding season (Dunn et al, 2020). The framework used in EIA to assess displacement effects (both mortality and reduced productivity) applies a pre-determined displacement rate to the number of birds recorded in an offshore wind farm footprint and then, using either an individual based model or expert opinion, the mortality rate of displaced birds is estimated (Warwick-Evans et al, 2017;Searle et al, 2018;JNCC, 2022). This framework assumes a percentage of birds in the wind farm footprint are excluded, i.e.…”

Alderney’s Northern Gannet Morus bassanus population; Counts on Les Etacs and Ortac

“…The second is an area to the east, from the northern tip of the Normandy peninsula to Le Havre, France. In these areas, there are a number of proposals for offshore wind farm developments, of which when built, Gannets may come into contact with the turbines (Warwick-Evans et al 2015a, 2016a, 2016b, resulting in low levels of mortality, likely to increase as wind farm area increases (Warwick-Evans et al 2018). Alderney's Gannets have been regularly monitored since they were first recorded in 1940 (Table 1) including during the four Britain and Ireland Gannet censuses: Operation Seafarer, the Seabird Colony Register, Seabird 2000 and the most recent census in 2005 (Cramp et al 1974;Hill 1989;Sanders & Harris 2005;Wanless et al 2005).…”

“…The aerial counts on Alderney have been complemented with annual productivity counts (Alderney Wildlife Trust 2016) and the mass-ringing of chicks (Veron & Lawlor 2009) to measure annual survival and gain insight into the distribution of these birds during the non-breeding season. Both juvenile and adult survival rates have increased over time, most likely due to their use of discards from fishing vessels (Votier et al 2013;Warwick-Evans et al 2016b).…”