Demographic estimates from radio‐tagging: models of age‐specific survival and breeding in the goshawk

• Published in: Journal of Animal Ecology
• Main Authors: Kenward, R. E., Marcström, V., Karlbom, M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1999
• Subjects: Accipiter gentilis
• Online Access: http://dx.doi.org/10.1046/j.1365-2656.1999.00347.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1046%2Fj.1365-2656.1999.00347.x; https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2656.1999.00347.x

Summary 1. Age‐specific survival and breeding (ASSAB) models were developed with data from 318 goshawks ( Accipiter gentilis L.) fitted during 1980–7 on the Baltic island of Gotland with tail‐mounted radio‐tags. 2. Comparisons with recaptures and recoveries of 238 ringed juveniles without radio‐tags detected no marking bias among hawks radio‐tagged at nests, nor survival bias from tag impacts or signal‐loss effects, but disproportionate adult deaths within a month of trapping. 3. Among 63 dead hawks found by radio‐tagging, 35% were killed by humans and 65% died from natural causes, mainly starvation. Ring recoveries over‐represented killing by humans. 4. Radio‐tagging estimated first‐year male survival rates of 0·49–0·54 to the next spring, lower than estimates of 0·69–0·71 for females; combined survival was higher than in contemporary ringing records. Excluding first‐month data from trapped adults, second‐year survival was 0·59 for males, 0·71 for females, and 0·79–0·83 for both sexes thereafter. 5. No hawks were observed to build nests or lay eggs in their first year. Only 8% of radio‐tagged females laid eggs in their second year, but 47% of older females. Second‐year males were as often as older males in egg‐laying pairs (70%), but were less likely to rear young. 6. Mark‐recapture of 351 goshawks ringed in nests estimated that 262 fledged on Gotland annually, from 151 nests with eggs. Emigration was 3% (SE ± 2%), with 1 ringed immigrant. 7. An ASSAB model with staggered‐entry survival estimates predicted no population change when based on males, with breeding success of 75% from laying to fledging, and a brood size of 2·27; independently recorded values for 165 nests were 75% (± 3%) and 2·24 (± 0·08). 8. The model required a 0·5% increase in female survival rate for equal numbers of hawks to pair, and an increase in fledging success from 73% to 75% for a balanced population with a brood size matching the 2·27 of males. The model estimated a male : female ratio of 1·0 : 1·78 in the adult population, with 71% ...