Many bird species are advancing the timing of their egg-laying in response to a warming climate. Little is known, however, of whether this advancement affects the respective length of the breeding seasons. A meta-analysis of 65 long-term studies of 54 species from the Northern Hemisphere has revealed that within the last 45 years an average population has lengthened the season by 1.4 days per decade, which was independent from changes in mean laying dates. Multi-brooded birds have prolonged their seasons by 4 days per decade, while single-brooded have shortened by 2 days. Changes in season lengths covaried with local climate changes: warming was correlated with prolonged seasons in multi-brooded species, but not in single-brooders. This might be a result of higher ecological flexibility of multi-brooded birds, whereas single brooders may have problems with synchronizing their reproduction with the peak of food resources. Sedentary species and short-distance migrants prolonged their breeding seasons more than long-distance migrants, which probably cannot track conditions at their breeding grounds. We conclude that as long as climate warming continues without major changes in ecological conditions, multi-brooded or sedentary species will probably increase their reproductive output, while the opposite effect may occur in single-brooded or migratory birds.

No abstract

Predation, the most important source of nest mortality in altricial birds, has been a subject of numerous studies during past decades. However, the temporal dynamics between changing predation pressures and parental responses remain poorly understood. We analysed characteristics of 524 nests of European reed warblers monitored during six consecutive breeding seasons in the same area, and found some support for the shifting nest predation refuge hypothesis. Nest site characteristics were correlated with nest fate, but a nest with the same nest-site attributes could be relatively safe in one season and vulnerable to predation in another. Thus nest predation refuges were ephemeral and there was no between-season consistency in nest predation patterns. Reed warblers that lost their first nests in a given season did not disperse farther for the subsequent reproductive attempt, compared to successful individuals, but they introduced more changes to their second nest sites. In subsequent nests, predation risk remained constant for birds that changed nest-site characteristics, but increased for those that did not. At the between-season temporal scale, individual birds did not perform better with age in terms of reducing nest predation risk. We conclude that the experience acquired in previous years may not be useful, given that nest predation refuges are not stable.

No abstract

Models of the evolution of parent‐offspring communication and of brood size assume that the noisy begging by the young is costly in terms of predation. The present study was designed to investigate cause‐and‐effect relations between the behaviour of the offspring and adult Meadow Pipits Anthus pratensis and the risk of nest predation. Harriers (Circus spp.), which can use auditory signals, were the main predators in the study area. I found that the intensity of vocal begging by broods did not influence their survival, despite the fact that the proportion of time that parents sacrificed to nest guarding declined with increased begging and some broods readily begged if a stimulus resembling the approaching parent was produced. The lack of fitness penalties for noisy broods was attributed to the following factors: (1) the open habitat was easy to scan, and parents silenced the young before feeding them if a predator was close (this adaptation was demonstrated in an experiment) and (2) parent birds could not deter harriers searching for prey, and therefore nest guarding did not influence the probability of nest detection. Pitfalls in the interpretation of relations between the vocal begging and the vulnerability to nest predation are discussed.

The rate of nest parasitism is a product of two interacting phenomena: host selection by cuckoos and defence by hosts. In our study area the rate of nest parasitism by cuckoos is significantly lower in the great reed warbler (GRW; Acrocephalus arundinaceus) than in the reed warbler (RW; A. scirpaceus), even though they breed in the same habitat and their reproductive biology is similar. We hypothesized that the difference in the proportion of parasitized nests may reflect a narrow selection of host by cuckoos (they prefer RW nests) or/and the relatively better alien egg discrimination in the GRW. In the egg discrimination experiment the GRW rejected the higher proportion of alien eggs than the RW. However, in both species the discriminative ability considerably varied in time, both within the day and within the breeding cycle. A logistic regression model suggests that the GRW would be a frequent host if only nest parasites could exploit the period of its lowest sensitivity to alien eggs. We conclude that the relatively low rate of nest parasitism in the GRW may reflect both its good discriminative ability and the low number of cuckoos that are specialized in dumping eggs to nests of this warbler. The adaptation of cuckoos to the particular host species may involve not only production of mimetic eggs, but also adjusting activity to temporal changes in sensitivity to alien eggs in the host.

No abstract

No abstract