Movements, sex-ratios, recovery rates and longevity of the Bearded Reedling Panurus biarmicus in Iberia

Abstract

The movements, sex-ratios, recovery rates and longevity of the Bearded Reedling Panurus biarmicus, according to the data obtained from the Spanish Ringing Office from 1975 to 2006, were analysed in this study. It was found that males moved greater distances and had shorter lives than females, and adults moved more and were longer lived than juveniles. Sex-ratios were male skewed and recovery rates were low, suggesting a high mortality in this species.

The Bearded Reedling Panurus biarmicus, a member of the family Paradoxornithidae (Robson 2007), is a highly dimorphic reed passerine, inhabiting large, fragmented wetlands across Europe (Gosler & Mogyorósi 1997). Three subspecies distributed across the Western Palearctic have been described and P.b. biarmicus breeds in western Europe (Cramp & Perrins 1993). The species is neither threatened nor a bird of conservation concern in Europe (Birdlife International 2004). In Spain, however, it was first classified as Near Threatened (NT) at the beginning of the century (López & Monrós 2004) and has since been revised as Critically Endangered (Peiró et al 2010). The estimated number of Spanish breeding pairs in 1998–2002 is low (650–1,100) compared to other European countries (France: 3,000–9,000, Italy: 4,000–10,000; BirdLife International 2004), and the species has a patchy distribution in central (Castilla la Mancha: 292–501), northern (Navarra: 87–148) and eastern Spain (Comunidad Valenciana: 172–295) (López & Monrós 2003).

Several aspects of its ecology across Europe have been well studied, such as breeding biology (Spitzer 1972, Bibby 1981a, 1981b), habitat selection (Hoi & Hoi 2001, Trnká & Prokop 2006, Beemster et al 2010), functional ecology (Romero-Pujante et al 2001, 2005), habitat management (Wilson 2005) or population dynamics (Wilson & Peach 2006, Surmacki & Stepniewski 2007, Wilson & Hartley 2007, Brichetti & Grattini 2008). In Spain, studies have been perfomed on some of these aspects (Peiró 1994, Peiró & Maciá 2002, Belenguer et al 2006, Peiró et al 2006, Albaiceta & Sanz 2007, López et al 2007, Peiró 2010, 2011). However, studies concerning the species movements in Iberia, particularly focusing on those wetland sites that may play an important role from international and national conservation concern, remain poorly understood (Burgess & Evans 1989, BirdLife International 2004, Albaiceta & Sanz 2007). The aim of this note is to analyse and discuss the sex-ratios, recovery rates, movements and longevity of the Bearded Reedling using ringing data collated by the Spanish Ringing Office.

A total of 221 recoveries of Bearded Reedling, collected between 1976 and 2006, were provided by the Spanish Ringing Office and used in this analysis (Peiró in Frías et al 2007). This total comprised 141 males and 80 females with 99 adults (Euring code 4), 58 juveniles (Euring code 3) and 64 of unknown age (Euring code 2) in the sample. After post-juvenile complete moult (Pearson 1975) adults and juveniles cannot be differentiated (Svensson 1992) so the Euring age code 2 cohort will contain both first-year birds and adults. Due to the large number of birds in this cohort, the recovery data were lumped into only two sex and age classes (males and females and adults and juveniles). Sex-ratio was inferred from recoveries: although it was influenced by the monthly distribution of the sample, it was male-skewed (χ ² = 31.411; P = 0.001; df = 11). Recovery rates were obtained dividing the number of total recaptures (adults and juveniles) by the number of ringed birds in each one of the years 1992, 1993, 2003 and 2005 (Cantos & Manzaneque 1993, 1994, Frías et al 2005, 2006), making it comparable to the years surveyed by Peiró (2011) in El Hondo Natural Park (Alicante, southeast Spain). The longevity was calculated as mean minimum days elapsed from ringing to recapture (alive or dead) and the distance was calculated as mean distance from ringing site to recapture site (Table 1). Differences among means (± SE) were tested by Mann–Whitney U-test in SPSS (v11; SPSS Inc. 2000). I used non-parametric tests because the whole sample did not meet criteria for normality (Kolmogorov–Smirnov test: Z = 4.282; P < 0.001; n = 221).

Table 1. Distance and time between ringing and recovery for all recoveries of Bearded Reedlings ringed in Iberia between 1975 and 2006. Means are given with SE, sample size and range.

	Distance (km)	Time (days)
Males	65.7 ± 22.8 (12) 8–283	318.0 ± 25.6 (141) 1–2,270
Females	20.3 ± 6.8 (8) 6–51	390.4 ± 35.2 (80) 4–1,609
Adults (Euring code 4)	82.7 ± 38.2 (7) 14–283	406.6 ± 32.8 (99) 4–2,270
Juveniles (Euring code 3)	0.0 (58)	204.5 ± 26.6 (58) 1–754
All recoveries	47.5 ± 14.6 (20) 6–283	344.2 ± 20.9 (221) 1–2,270

The average distance between ringing and recovery location for all records was 47.5 ± 14.6 km (median: 31.5 km) and only 5% of birds recaptured (n = 10) had moved more than 50 km. Males moved on average 45 km further than females but this difference was not statistically significant (U = 27.00; P = 0.103; df = 20). The time between ringing and recovery varied between one and six years (Table 1) with the greatest longevity record being 6.2 years, which classifies this bird as a typical R-specialist or “fast bird” (Pianka 1970, Bibby 1981b). Although the longevity of males was less than for females, this difference was not significant (U = 476; P = 0.062; df = 221), and longevity was significantly greater in adults than in juveniles (U = 1629.5; P < 0.001; df = 157; Table 1). Using recovery data, the sex-ratio of Bearded Reedling was significantly male skewed (0.63; 141 males: 80 females; χ ² = 16.37; P < 0.001; df = 1). The average recovery rate was, overall, medium to low at 3.0% ± 1.31 (n = 4, range 0–6.4%).

Despite the paucity of published data on movements and longevity in this species (Axell 1966, Hořák et al 2003), the maximum longevity calculated for Iberian Bearded Reedlings was similar to that given in the literature (six years; Cramp & Perrins 1993, Hořák et al 2003) and the distance covered by Bearded Reedlings was less than found in Czech Republic and Slovakia for the average distance from birthplace of young birds (70.7 km; Hořák et al 2003). This study is concordant with the findings of Peiró (2011) in El Hondo Natural Park in that sex-ratios of ringed birds were male skewed in a nearly identical proportion (0.62). These figures are slightly less than given for birds ringed in the Ebro Valley (northwest Spain) by Albaiceta & Sanz (2007) (0.69) and similar to that given in recoveries of Czech and Slovak Bearded Reedlings (0.64) by Hořák et al (2003). Peiró (2011) proposed the hypothesis that females disperse further and are more likely to be predated, which is not in accordance with the findings of this study. I propose the new hypothesis that, in a broader scale, males and juveniles are shorter lived than females and adults due to greater dispersal, leading to a higher risk of mortality. This is supported by the significant difference in longevity among ages.

ACKNOWLEDGEMENTS

This note is dedicated to the memory of Dr Mariano López Maciá, an expert ringer of Bearded Reedlings in southern Alicante. I am grateful to Jesús Pinilla, from the Spanish Ringing Office, who provided me with the recovery data and to all the ringers that contributed by ringing Bearded Reedlings in Spain.