Mark-resighting analysis of a California gull population

Abstract

SU MMA RY C alifornia gulls (Larus californicus) of known age and sex were censused on their breeding colony in 1979, 1980 and 1984 through 1993. Ages of 235 males and 196 females ranged from 4 to 27 years. Age classes used in the analysis were limited to 17, 4 through 19, and 20 or more as a ® nal age category because data on gulls over 20 were sparse. Survival declined with age in a way that was parsimon iously modelled with a quadratic function. Other factors, sex and time, did not explain any variation in survival. Resighting depended on age, sex and time. Younger adu lts skipped breeding more frequently than did older adults, and females skipped breeding more frequently than did males. There was also good evidence for time dependence in resighting probability, but its inclusion in the model occurred at the expense of interpretability and precision. In a data set such as this, resighting probability may assume more importance than a merè nuisance parameter' . In this study, resighting history measured attendance at the breeding ground . In turn, attendance rates may be a manifestation of reproductive strategy, which can also have consequences for survival. In this situation, there may be heterogeneity in both survival and resighting probability that is unexplained by the model. W hile such complexity may well be a nuisance to deal with, it can also point to important biological questions.

Food availability and nest predation influence life history traits in Audouin's gull, Larus audouinii

“…Suitable ecological conditions at the Ebro Delta (protection against human disturbance, habitat suitability, low levels of interspeci®c competition with yellow-legged gulls, and high food availability; Oro et al 1996a,b) have probably contributed to low variability in adult survival, in contrast to that recorded in some long-lived species living in highly variable enviromnents (e.g., Kanyamibwa et al 1990;Chastel et al 1993;Coulson et al 1997). The estimated adult survival rate in Audouin's gull (91%) is very close to those recorded for other gull species (88% in herring gull: Pons and Migot 1995;Wanless et al 1996; 91% in lesser black-backed gull: Wanless et al 1996; 90% in common gull L. canus: Rattiste and Lilleleht 1995; 91% in California gull: L. californicus: Pugesek et al 1995; 90% in black-headed gulls L. ridibundus: Pre vot-Julliard 1996). Neither age (varying from 3 to 8 years) nor sex had a signi®cant eect on Audouin's gull survival, con®rming previous results for other gull species (Pons and Migot 1995;Pugesek et al 1995;Rattiste and Lilleleht 1995;Pre vot-Julliard 1996;Wanless et al 1996).…”

“…The estimated adult survival rate in Audouin's gull (91%) is very close to those recorded for other gull species (88% in herring gull: Pons and Migot 1995;Wanless et al 1996; 91% in lesser black-backed gull: Wanless et al 1996; 90% in common gull L. canus: Rattiste and Lilleleht 1995; 91% in California gull: L. californicus: Pugesek et al 1995; 90% in black-headed gulls L. ridibundus: Pre vot-Julliard 1996). Neither age (varying from 3 to 8 years) nor sex had a signi®cant eect on Audouin's gull survival, con®rming previous results for other gull species (Pons and Migot 1995;Pugesek et al 1995;Rattiste and Lilleleht 1995;Pre vot-Julliard 1996;Wanless et al 1996). However, future analysis involving older age classes might detect a senescence eect (i.e., a decline of survival with older age), as recorded in other Laridae (Aebischer and Coulson 1990;Pugesek et al 1995).…”

“…We ®rst tested the hypothesis that food supply would aect breeding performance but not adult survival, since gulls are long lived and adult survival is the most sensitive demographic parameter in their population dynamics (Stearns 1992). If we assume that costs of reproduction are similar for both sexes and independent of their age, as recorded for other gull species (e.g., Pons and Migot 1995;Pugesek et al 1995;Rattiste and Lilleleht 1995;Pre votJulliard 1996;Wanless et al 1996), adult survival is expected to be constant with age (before the eects of senescence for the oldest ages) and sex (although see Aebischer and Coulson 1990;Pugesek and Diem 1990;Pyle et al 1997).…”

Estimating Animal Abundance: Review III

“…The CJS modeling framework can be used to investigate this question, as was done indirectly by Pugesek et al (1995), and directly by Nichols, Hines and Blums (1997) who modeled a linear-logistic decline in survival as a function of age.…”

“…Pradel (1993) showed how to modify the CJS model to account for trap-dependence by splitting the complete capture history into a series of sub-histories and modeling the first occasion after release differently than subsequent survival periods. This was extended in Pugesek et al (1995) to account for both age and trap-dependence effects.…”