Summary

1. It is widely accepted that the arrival order of migratory birds is correlated with the condition of the birds, which leads to high quality individuals occupying prime sites. However, the theoretical backgrounds for this argument have been lacking. A simple game-theoretic model of arrival timing is provided which investigates the evolutionary stability of condition-dependent arrival order in territorial migrant birds.



2. Competition for territories or other priority-dependent benefits can lead to arrival dates far preceding the cost-minimizing date (the optimum date in the absence of competition) for all but the weakest individuals. Increasing the number of competitors can generate a ‘cascading’ competition for early arrival, which advances arrival dates further apart from the individual optimum dates for the onset of breeding.



3. At equilibrium, arrival order corresponds strictly to condition order only if marginal costs of advancing arrival are always larger for individuals in lower condition. If spring mortality vacates territories for later-arriving birds, the criterion for ‘honest’ arrival order becomes still stricter: differential survival costs should exist, but survival differences among individuals (or, alternatively, territory quality differences) should not be very large.



4. If the habitat is saturated so that there is a risk of not obtaining a territory at all, or if worst territories are of much lower value than the rest, competition may lead to the majority of the population arriving within a fairly short interval, followed by a much later floating fraction. This synchrony in the arrival of breeders imposes an increasing cost for the lesser fit breeding birds. Thus, arrival costs paid are not necessarily highest for earliest arriving individuals, but for those who have the most to lose if they drop a few steps in the arrival order.



5. Competition for high quality territories can also lead to partial migration, in which case birds in good condition are expected to be most likely to remain resident.

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Competition for early arrival in migratory birds

The oscine passerines, or 'songbirds', are one of the few animal taxa in which individuals learn their vocal signals. Recent comparative studies reveal a remarkable diversity of song-learning strategies in the songbirds. Here, we discuss recent studies that shed light on the possible functional basis of different song-learning programs. We argue that further insights into the evolution and ecology of song learning will require that comparative data and functional hypotheses be analyzed in a phylogenetic context, and we review recent studies that we feel might be the first steps in this process.

https://faculty.washington.edu/beecher/B&B-TREE.pdf

Functional aspects of song learning in songbirds

http://www.tau.ac.il/~lotem/pdf/Anim95.pdf

Constraints on egg discrimination and cuckoo-host co-evolution

An examination of about 12000 clutches of European passerines that contained eggs of the common cuckoo (Cuculus canorus), held in museum egg-collections, revealed statistically significant correlations between the cuckoo and the host eggs within a clutch in volume, ground colour, and size and percentage coverage of the spots. Although most cuckoo eggs were yellowish, the range in coloration and the percentage coverage of spots indicate that in these respects the cuckoo eggs are distributed along a continuum. However, a similar distribution was also found among the pooled host eggs. These results provide some support for the ‘host preference hypothesis’, which states that each cuckoo female specializes on one particular host species.

By using a subjective classification, we found that there are at least 15 different cuckoo egg-morphs in Europe, but only 44% of the clutches contained cuckoo eggs of the egg-morph corresponding to the host eggs. The ‘host preference hypothesis’ therefore cannot provide a satisfactory explanation for the variation found among cuckoo eggs in Europe. However, 77% of the cuckoo eggs had been laid in nests of hosts with nesting sites similar to those of the main host of the egg-morph. This indicates that cuckoos also parasitize several species whose nest sites are similar to those of their main host. These results therefore provide support for the ‘nest site hypothesis’ which states that each cuckoo female parasitizes a group of host species with similar eggs or nest sites. The ‘natal philopatry hypothesis’ which states that female cuckoos may search for nests completely at random in their natal habitat is only weakly supported and can probably be rejected.

Most of the hosts, main and secondary, nest among low vegetation or on the ground, whereas tree-nesting species are seldom parasitized. The most frequently used hosts in the egg collections we examined were species of the Acrocephalus and Sylvia genera of warblers, all species that breed in low vegetation.

Egg‐morphs and host preference in the common cuckoo (Cuculus canorus): an analysis of cuckoo and host eggs from European museum collections

MANY STUDIES OF sexual selection have focused on the role of ornaments in mate choice (see Andersson 1994, Espmark et al. 2000). Birds have been a favorite taxon for those studies because of the prevalence of conspicuous ornaments, including brightly colored feathers, skin, and bills, and dramatically elongated feathers or feathers of elaborate structure. The colors of avian ornaments are the result of carotenoids, melanins, tissue structure, or some combination thereof. Carotenoid ornaments (e.g. bright reds, oranges, and yellows) have generated much interest. Those pigments can not be synthesized de novo by animals, but rather must be included in the diet (Brush 1990). That allows for the possibility that they are limited in nature or diffi cult to obtain (Hill 1994, 1996; Hudon 1994; Linville and Breitwisch 1997). Additionally, carotenoids have been implicated in a variety of critical physiological functions in animals. That recognition has stimulated much recent research on mate choice of carotenoid advertisement and the indicator value of carotenoid ornaments for several important aspects of individual condition. Avian melanin ornaments have also received considerable research attention. In contrast to studies of carotenoid ornaments, however, the primary focus of studies of melanin ornaments has been on the advertisement of melanin “badges” in intrasexual competition. Thus, the associations among expressions of melanin ornaments, mate choice, and individual condition have not been made to the same degree as for carotenoids. There are several possible reasons for that. First, melanins not only color ornaments but are also the basis of most inconspicuous appearances (i.e. camoufl age), in contrast to the highly conspicuous carotenoids. Second, melanins are synthesized by animals and thus do not need to be included in the diet. Finally, it is perhaps incorrectly assumed that melanin ornaments are typically black or blackish-brown and thus show both less variation within species and less diversity across species than do carotenoid ornaments. Here, we review a variety of aspects of the biology of avian melanin ornaments. We demonstrate that the color diversity of melanin ornaments is quite broad, including red (e.g. Red Junglefowl and Barn Swallow [Hirundo rustica]), orange (e.g. Red Junglefowl), yellow (e.g. Western Tanager [Piranga ludoviciana]), and green (e.g. Mallard), in addition to black and brown. Color differences in all melanin ornaments are, in part, a function of the ratio of the two types of melanins contained, and we outline the intriguingly different metabolic pathways to the formation of the two different categories of melanins. There are likely to be both signifi cant physiological benefi ts and costs to melanin production, and those may well differ for the two types of melanins. Finally, we Department of Biology, University of Dayton, Dayton, Ohio 45469-2320, USA JODIE M. JAWOR1 AND RANDALL BREITWISCH MELANIN ORNAMENTS, HONESTY, AND SEXUAL SELECTION The Auk 120(2):249–265, 2003

Melanin ornaments, honesty, and sexual selection

Responses of 33 potential host species towards a non-mimetic, dummy, cuckoo egg placed in their nest were tested (N = 372). For 22 of these species, their behavioural responses towards a dummy cuckoo placed near their nest were also tested (N = 193). The species were grouped in A) most common hosts: species which at the moment are losing out in the coevolutionary arms race with the cuckoo and which today represent favorite hosts; B) frequently-used hosts: species which at the moment are assumed to be true cuckoo hosts, but which are not so commonly used as those in group A; C) rarely-used hosts: species which would appear to be suitable hosts, but which despite of this, are rarely used. These species are assumed to be ahead of the cuckoo in the coevolutionary arms race; D) unsuitable hosts: species with a breeding biology which either prevents, or counteracts, cuckoo parasitism. They are therefore assumed never to have been engaged in a coevolutionary arms race with the cuckoo. In the most common hosts the median acceptance rate of the non-mimetic egg was 86 % , in the frequently-used hosts 33 % , in the rarely-used hosts 10 % and in the unsuitable hosts 100 %. In the most common hosts the median rate of aggression shown towards the cuckoo dummy was 50%, but the most numerous species in this group, the meadow pipit, showed aggressive behaviour in 60% of the cases. The median aggression rate both in the frequently-used hosts and the rare hosts was 100 % and in the unsuitable hosts 0%. The bluethroat was the only species which accepted the non-mimetic dummy egg at a higher rate later on during the incubation period than during earlier stages. A positive correlation was found between the power of egg discrimination and the rate of aggression shown towards the dummy cuckoo. Such aggression was stronger when both parents were present at the nest than when only one parent was present. The results of this study lend support to the hypothesis that the differences in the degree of responses by the host species towards parasitism by the cuckoo reflect different stages in a continuous coevolutionary arms race with cuckoos.

Behavioural Responses of Potential Hosts Towards Artificial Cuckoo Eggs and Dummies

Song structure reflects male quality in pied flycatchers, Ficedula hypoleuca

The main objectives of this study were to provide a thorough description of the advertising song in the male pied flycatcher Ficedula hypoleuca and examine the complexity of the song and its variability within and between breeding seasons by qualitative and quantitative analyses of its structure. Songs were recorded from 117 males in central Norway in one or more of the three stages of the breeding season: before pairing, during nest building, and in the laying/brooding stage. Eight males were recorded both before and after pairing, and 13 males were recorded in two consecutive years. Spectrographic analyses were based on 25 consecutive song strophes per male. When the males became mated their song changed in a number of ways: in addition to reduced singing activity, the number of figures and figure types in the song strophe became fewer at the same time as the song strophe became shorter. There was also a tendency towards increasing song versatility and decreasing repertoire size. Individual mal...

Helene M. Lampe

Papers

Behavioural Responses of Potential Hosts Towards Artificial Cuckoo Eggs and Dummies

Song structure reflects male quality in pied flycatchers, Ficedula hypoleuca

Variations in the song of the pied flycatcher within and between breeding seasons

Size of males' song repertoires