Local annual survival of booming male Great Bittern Botaurus stellaris in Britain, in the period 1990–1999

Abstract

Male Great Bitterns Botaurus stellaris have individually distinctive boom vocalizations which have been used since 1990 to count the British population accurately. We used vocal individuality to identify birds between years and analyse the survival of the British booming population. We used six instances of Great Bitterns known to be the same birds (from radio tracking and re‐sighting of darvic rings) in successive years to provide a means of identification independent from vocalizations. All of these birds remained in the same territory from one year to the next. Seven spectrogram measures were chosen as quantitative descriptors of Great Bittern booms. Boom similarity was expressed in terms of Euclidean ‘acoustic’ distance between descriptors of pairs of birds. Great Bitterns that were known to be the same birds had more similar booms across years than those known to be different. The acoustic distances and knowledge of site fidelity were used to construct parsimonious rules on which to base re‐identification decisions and to build survival histories. Great Bittern local survival in Britain as a whole was estimated as 70% (± 5.1 se) with survival in north‐west England (at Leighton Moss) higher (82.8%, ± 7.3 se) than that in East Anglian sites (65.2%, ± 5.4 se) (χ12 = 3.4, P = 0.07). Movements of males between years were apparent between sites within the Suffolk and Norfolk coastal regions but not on a large scale. Survival of adult males in East Anglia was positively related to winter rainfall, but there was no significant relationship with winter temperature. There was a positive relationship between the annual population change in East Anglia and the annual local adult survival rate.

Protected areas facilitate species’ range expansions

“…The five focal species that colonized PAs significantly more frequently than expected (Table 1) likewise benefit principally from the habitats provided within PAs, just like habitat specialist butterflies (Fig. 4), with the benefits deriving from both the predesignation condition of sites and the subsequent postdesignation improvement of habitat quality (23)(24)(25)(28)(29)(30) (SI Materials and Methods).…”

“…The first analysis considers PA use by seven localized but, nonetheless, expanding species (five birds and two butterflies) that have been subject to exhaustive repeat surveys, during which potential breeding sites have been surveyed irrespective of the PA status of the land (23)(24)(25)(26)(27)(28)(29)(30) (Table 1 and SI Materials and Methods). These species are the only expanding species in the United Kingdom (UK) for which such high-quality data are available.…”

Monitoring habitat quality and condition of Queen Charlotte saw-whet owls (Aegolius acadicus brooksi) using vocal individuality.

“…Perhaps the longest-term study employing measures of vocal individuality was to monitor annual survival of great bitterns (Botaurus stellaris) over a 10-year period (Gilbert et al 2002). The authors of this study pointed out some important biases in using this as a long term monitoring tool.…”

“…The authors of this study pointed out some important biases in using this as a long term monitoring tool. First, if only one of the sexes is vocal, there is an obvious lack of Chapter 1 : General Introduction knowledge about the survival and behaviour o f the other sex (Gilbert et al 2002). Hence, in studies utilizing vocal individuality to monitor males for instance, care must be taken to not extrapolate the findings to females without proper justification.…”

“…Gilbert et Chapter 1 : General Introduction al. 1994, McGregor andByle 1992), this tool can be applied for both monitoring within year movements and estimating levels o f site fidelity and territory turnover between years (Delport et al 2002, Gilbert et al 2002, Galeotti and Sacchi 2001.…”