Sex-specific differences in site fidelity and the cost of dispersal in yellow-headed blackbirds

Male migratory birds tend to be more faithful than females to previous breeding sites, suggesting sex differences in costs or benefits of dispersal. In Illinois, greater site fidelity by male yellow-headed blackbirds (Xanthocephalus xanthocephalus) was associated with reduced reproductive success the following year for dispersers relative to non-dispersers. Dispersing females suffered no reduction in reproductive success the following year. Males that attracted few social mates, and thus had low reproductive success, were more likely to disperse, whereas females dispersed in response to low-patch reproductive success, regardless of their individual performance. Males that dispersed appeared to be successful acquiring territories because none was observed as a floater. The rate of dispersal by males in this low-density population was greater than in more dense populations where dispersing males may be less successful at acquiring territories. Despite success at obtaining territories, males that dispersed acquired territories on the periphery of wetlands where fewer females nested, resulting in lower reproductive success. In the second year after dispersing, however, males moved onto more central territories where they acquired larger harems. Thus, dispersal by males may be a long-term strategy requiring at least 2 years for benefits to be realized. Long-term success was enhanced because dispersing males moved to wetlands on which reproductive success was higher than on the wetlands they left. In addition to demonstrating that both individual and patch reproductive success affect dispersal decisions, these data indicate that when evaluating costs and benefits of dispersal, researchers should use a time frame beyond 1 year.     

Site fidelity and territorial movements of males in a rapidly declining population of yellow-headed blackbirds

We tested several hypotheses to explain low between-year territory fidelity in a breeding population of yellow-headed blackbirds (Xanthocephalus xanthocephalus). During a 5-year study the population of territorial males declined by two-thirds and some of the marshes that supported territories significantly deteriorated. Individual males held territories and bred for an average of 1.9 years. Of males that bred for at least 2 years, 30% skipped owning a territory in the study area during at least 1 year of their breeding lifetimes. Our information suggests that they may have bred outside of the area in those years. Of males with territories in two or more breeding seasons, 60% changed breeding marshes at least once. Males changed territories during 42.9% of between-year opportunities to do so. We found no support for the hypotheses that male yellow-headed blackbirds: (1) are more likely to move when territory density is low; (2) are likely to abandon territories that are deteriorating; or (3) change territories to improve their reproductive success. We suggest three non-mutually exclusive explanations for the yellow-headed blackbird's weak site fidelity: (1) it is a response to habitat deterioration and to other factors that may be causing the population's decline; (2) the males, being migratory, make fresh settlement decisions each year after they arrive on the breeding grounds in the general vicinity of their previous year's breeding; (3) yellow-headed blackbirds may have evolved in, and be adapted to, highly unstable habitats, moving frequently in response to changes in local breeding site conditions. Correspondence to: L.D. Beletsky     

Long-term mate and territory fidelity in neotropical buff-breasted wrens (Thryothorus leucotis)

Among sedentary species, mate and site fidelity may be imposed by year-round territoriality and high annual survivorship, both of which theoretically lead to few opportunities to move between mates and breeding territories. We examined mate and territory fidelity in sedentary neotropical buff-breasted wrens (Thryothorus leucotis) in relation to the opportunities to divorce (vacancies on neighbouring territories), breeding experience and site of origin (within vs outside local breeding population). Overall, buff-breasted wrens showed high rates of mate and territory fidelity between years, with individuals significantly more faithful to their territories than to their partners. Mate and territory fidelity was not forced upon buff-breasted wrens, as most individuals had opportunities to switch mates and territories. However, this was not uniform among all individuals. Individuals that had bred together displayed 100% mate and territory fidelity despite the fact that males and females in almost all experienced pairs had opportunities to switch mates and territories. Local recruits (philopatric offspring that acquired territories in the local breeding population) also displayed mate and territory fidelity, but fidelity occurred because recruits rarely had the opportunity to divorce prior to initiating their first breeding attempt. By contrast, almost half of all territorial individuals that originated outside the local breeding population (immigrants) had opportunity to divorce, with approximately two thirds of them switching mates and territories. Divorces occurred within the first 5 months of pairing, suggesting that immigrants may have sampled mates and territories before forming permanent partnerships.     

Territoriality among male red-winged blackbirds

Summary We examined male site fidelity and territorial movements in a population of individuallyidentifiable red-winged blackbirds (Agelaius phoeniceus) over an 8-year period. Based on general theory and knowledge of the ecology of this population, we predicted that males would be site conservative, and that they would voluntarily change territories only when they could expect to improve significantly their reproductive success. Because males are absent from their territories for only short periods, and probably have accurate comparative information only about nearby territories on which to base their decisions, we predicted that most moves would be over short distances. About 70% of males that bred for more than 1 year retained their original territories between breeding years. Most of the 30% of males that changed territories moved less than 200 m, often to adjacent territories. As predicted, males moving less than 200 m tended to have better reproductive success after moving than before, whereas long distance movers did not improve their success after moving. Territorial male redwings appear to monitor breeding activity on nearby territories and move when significant potential benefits are perceived and opportunities exist. Long-distance moves may be involuntary ones. The amount of information possessed about present and alternative sites, and the time and opportunity required to collect the information, are probably major constraints influencing site conservatism in this and other territorial species.     

Site fidelity of male Galápagos sea lions: a lifetime perspective

Knowledge about the distribution of resources can lead to the development of spatial preferences and long-term site fidelity. Individuals are expected to choose sites that best suit their needs. However, dominant individuals restrict movements of less competitive ones. Accordingly, one may expect spatial preferences to differ with regard to individual characteristics and to change over time. We investigated lifetime changes of site fidelity patterns with regard to reproductive success in male Galápagos sea lions (Zalophus wollebaeki). Showing a high degree of natal philopatry in the first 2 years of life, non-territorial males pass through a stage of fidelity to their natal colony where they develop preferences for areas outside prime breeding areas. Variation in the degree of spatial preferences was not associated with age or size, characteristics linked to an individual’s dominance status. For non-territorial males, roaming proved to be an adequate strategy to gain reproductive success. Only the most competitive males established territories in areas preferentially visited by females. They had a high probability to return to breeding areas where they successfully reproduced in previous seasons. Overall, the results reveal lifetime changes in site fidelity with regard to male status. The degree of site fidelity observed within the colony suggests familiarity and thus a high degree of tolerance among individuals using the same areas. This seems to facilitate attendance in the colony and thus the possibility to prospect for oestrus females.     

Mate choice in the brown thornbill (<Emphasis Type="Italic">Acanthiza pusilla</Emphasis>): are settlement decisions,divorce and extrapair mating complementary strategies?

In socially monogamous birds, females may express mate preferences when they first select a breeding partner, through divorce and subsequent breeding dispersal to a new partner and through extrapair mating. We examined settlement patterns, divorce and breeding dispersal in a sedentary Australian passerine, the brown thornbill (Acanthiza pusilla), in relation to two traits known to influence extrapair paternity (male age and male size). Settlement decisions, divorce and territory switching behaviour were all female strategies that reduced their likelihood of breeding with 1-year-old males. Females preferred to settle in territories with 2+ -year-old males, were more likely to divorce 1-year-old males, and only switched territories if they had an opportunity to form a new pair bond with an old male. In contrast, female settlement and divorce decisions were not influenced by male size. Female thornbills obtain a direct benefit from preferring older males as social mates because breeding success improves with male age in brown thornbills. Nevertheless, divorce rates in this species were low (14% of pair bonds were terminated by divorce), and individuals rarely switched territories following the death of a mate. Both of these mating strategies appeared to be primarily constrained by the distance adults moved to initiate a new pair bond (1–2 territories) and by the limited availability of unpaired older males in the immediate neighbourhood.Communicated by M. Webster     

Aggressiveness of breeding territorial honeyeaters corresponds to seasonal changes in nectar availability

Summary On the east coast of Australia, new holland and white-cheeked honeyeaters experience huge seasonal changes in nectar availability over their breeding periods. I observed breeding males of both species to determine whether levels of territorial aggressiveness varied with these changes in nectar availability. I watched individual males repeatedly and assessed their aggressiveness by recording their responses to birds that came within 30 m of them. Almost all attacks were on unfamiliar birds; males never attacked their mates or offspring and rarely attacked other birds that were resident in the area. Intruders were most likely to be attacked if they were conspecifics, if they landed rather than flying by, and if they came near the centers of males' territories. Taking into account the types, behaviors, and locations of intruders, there were pronounced seasonal changes in the probability of an intruder being attacked by a territorial male. Males were least aggressive when nectar was abundant, suggesting that territorial aggression could be at least partially a response to scarcity of nectar. Seasonal changes in aggressiveness were not accounted for by breeding cycles or by changes in frequency of intrusions.     

Effects of male removal on female foraging behavior in the Eurasian treecreeper

In old, spruce-dominated forests of central Finland, Eurasian treecreepers Certhia familiaris divide their territories spatially during the breeding season. Females forage primarily on the upper parts of the tree trunks, while males use the lower parts of the tree trunks. In this study we removed males from eight territories in the early nestling period to see if the mate's absence would change the foraging patterns of the resident female. Widowed females foraged at lower heights, thus behaving more like paired males. These females also spent less time on each tree and on each foraging bout than did paired females. We conclude that male removal facilitated the change in a female's foraging niche and foraging time at the trees. Females may re-optimize their foraging site selection owing to the absence of dominant males and a consequent need to increase their parental care. Behavioral plasticity may be the mechanism of niche partitioning between the sexes in this species. Received: 28 June 1996 / Accepted after revision: 27 March 1997     

Territory defence in tropical birds: are females as aggressive as males?

Much of our knowledge concerning the functions of territorial behaviour and how territories are defended by individuals comes from research on birds. The vast majority of this work has focused on temperate zone breeding territoriality in which territories are defended most obviously by males. Our understanding of the female role in territory defence is limited because they are less conspicuous and much harder to observe. We studied sex roles in territory maintenance and defence in a duetting, resident neotropical passerine, the white-bellied antbird (Myrmeciza longipes). This species maintains territories and pair bonds year round and both sexes sing and actively participate in territory defence. We performed a series of playback experiments throughout the dry (non-breeding) and wet (breeding) seasons. We exposed territorial pairs to three types of stimuli including: (1) single sex, male only songs, (2) single sex, female only songs, and (3) both sex songs/duets. Contrary to findings for most other tropical species, individuals defended their territories with equal levels of aggression regardless of stimuli. Furthermore, sex roles were very different, with males responding more aggressively than females to all stimuli throughout both seasons. Both males and females consistently responded more aggressively to territorial intrusions during the dry season than during the wet season, likely because food abundance is low in the dry season and territory value is high. Our analysis of duetting behaviour suggests that duets do not serve a significant role in mate guarding, or territory defence.     

Territory takeover and sexually selected infanticide in tropical house wrens

Summary Tropical house wrens in lowland central Panama are, with rare exception, permanently monogamous. During a 3-year demographic study of 54–56 pairs of these brids, both males and females committed infanticide in association with takeover of breeding territories. New males and new females replaced previously identified (color-banded) parents before the termination of parental care in 13% of 328 breeding attempts. Replacement was accomplished by physical takeover in at least some if not all cases. Total nest failure at the egg, nestling, or fledgling stage occurred in 73% of the male replacements and 70% of the female replacements. Nest predation was excluded as a possible cause of nest failure. 76% of male replacements and 50% of female replacements bred in the same season. Infanticidal replacement males bred sooner than did non-infanticidal males arriving at similar stages of the nesting cycle. Contexts in which infanticide occurred included takeovers by first-year males and females of territories and mates, re-entry into the breeding population by males that had recently lost their mates, acquisition of neighboring females by bigamous males, and the elimination of one female of a bigamous male by the other. Sexually selected infanticide in these birds is promoted by a lengthy breeding season and extremely limited breeding opportunities for individuals not already part of the breeding population. Mate limitation appears to be more important than habitat or nestsite limitation in restricting new breeding opportunities once the breeding season has begun.     

Nonideal breeding habitat selection: a mismatch between preference and fitness

The selection of breeding sites in heterogeneous habitats should ideally be based on cues closely reflecting habitat quality and thus predicting realized individual fitness. Using long-term population data and data on territory establishment of male Northern Wheatears (Oenanthe oenanthe), we examined whether territory characteristics linked to individual fitness (reproductive performance and survival) also were linked to territory preference. Breeding territories varied in their physical characteristics and their potential effects on reproductive performance, and this variation among territories was correlated from one year to the next. Of all measured territory characteristics (from the focal and the previous year) only territory field layer height predicted individual fitness, i.e., reproductive performance was higher in territories with permanently short rather than growing field layers. Territory preference, instead, was only linked to the size of territory aggregations, i.e., males settled earlier at territory sites sharing borders with several adjacent sites than at those with few or no adjacent sites. This mismatch between territory characteristics linked to fitness and those linked to territory preference was not explained by site fidelity or compensated for by the different fitness components measured. Because the results were not in agreement with an ecological trap scenario, where poor habitats are preferred over high-quality habitats, our results suggest a more general case of nonideal habitat selection. Whereas nonideal selection with respect to territory field layer height may be explained by its poor temporal predictability within the breeding season, the preference for territory aggregations is still open to alternative adaptive explanations. Our study suggests that nonideal habitat selection should be investigated by direct estimates of preferences (e.g., order of territory establishment) and their links to habitat characteristics and fitness components. Furthermore, we suggest that the probability of establishing a territory needs to be included as a factor influencing patterns of habitat selection.     

Polygyny in the red-winged blackbird: do females prefer monogamy or polygamy?

Five hypotheses have been proposed to explain polygyny in the red-winged blackbird (Agelaius phoeniceus). We categorized the hypotheses into three groups based on female preference for unmated versus monogamously mated males: (1) the “polygyny threshold” model, “sexy son” hypothesis and the “asynchronous settlement” model, which assume that females prefer unmated males to mated males on breeding situations of homogeneous quality; (2) the “neutral mate choice” hypothesis, which assumes that females have no preference; and (3) the “cooperative female choice” model, which assumes that females prefer monogamously mated males to unmated males. We tested the direction of female preference in two field experiments. In both experiments, newly settling females were given a choice of two adjacent territories, one defended by an unmated male and the other by a monogamously mated male. Male mating status was randomized with respect to the variation in territory quality and male quality. Early in the breeding season, significantly more females settled with the unmated males than with the mated males. Although more females settled with the unmated males than with the mated males late in the breeding season, the difference was no longer significant. Female settlement late in the season appeared to be related to the tenure of the resident females: the new females avoided territories where the resident females were in early stages of their nesting, but settled on territories where the resident females were in late stages. The pattern of female settlement shows that females prefer unmated males to mated males. The preference is consistent with the polygyny threshold model, sexy son hypothesis and the asynchronous settlement model, and inconsistent with the neutral mate choice hypothesis and the cooperative female choice model. For this reason, the latter two hypotheses are unlikely to explain the occurrence of polygyny in our population of red-winged blackbirds. Received: 1 December 1994 / Accepted after revision: 28 October 1995     

Pair and extra-pair mating success relative to male quality in red-winged blackbirds

We tested whether the reproductive success of male red-winged blackbirds (Agelaius phoeniceus) varied with male secondary sexual traits or with haematozoa prevalence, and whether these patterns were consistent with females preferring genetically superior males. We also determined whether the traits that correlated with male success on their own territories were also correlated with male success at siring young on other males territories. Our analysis included data from a 6-year study involving 617 nestlings for which paternity was determined by DNA profiling. Larger males sired more young on their territories, principally because they obtained larger harems. The success of larger males at acquiring more mates did not appear to be a consequence of larger males holding larger or better-quality territories. Older and longer-lived males sired more young by extra-pair fertilizations. Larger males sired the most offspring overall (on territory + off territory). Variation in epaulet size and color, responses to male and female models, nest defence and parasitism was not correlated with male success either on or off their territories or overall. Male success in a given year was significantly correlated with success the previous year, as expected if females were selecting genetically superior males. The male that was by far the most successful individual in this study was highly consistent from year to year. Because male body size is positively correlated with survival in this population (although not within the sample of males included in this study), female preference for larger males may have reflected a general preference for males with superior Survival ability. We propose that the direct advantage realized by older males in extra-pair matings might indicate that experience is important, such that experienced males are better at creating or exploiting the opportunities for extra-pair mating. This hypothesis is consistent with a pairwise analysis of cuckoldry that showed that cuckolders were most often older than the males they cuckolded.     

Natal philopatry and breeding area fidelity of long-billed curlews (Numenius americanus): Patterns and evolutionary consequences

Summary Long-billed curlews (Numenius americanus) appear unique among scolopacid shorebirds so far studied in possessing a significant sex bias in natal philopatry. We resighted 9 curlews at least attempting to breed that were color-banded as chicks; 8 of these were males. Male curlews also cooperate extensively with neighbors in mobbing potential chick predators. This mutualistic behavior may have evolved through kin selection among philopatric males. If so, we would expect such an evolutionary consequence to lead to a similar sex bias in breeding area fidelity. Yet our resightings of colorbanded adults over 4 consecutive years indicate that males and females were equally likely to return to previous nesting territories. Excessive disturbance such as capture and nest loss within a single breeding season was correlated with the likelihood of breeding dispersal by females but not males. This suggests potentially stronger breeding area fidelity of males.     

Male's return rate, rather than territory fidelity and breeding dispersal, explains geographic variation in song sharing in two populations of an oscine passerine (Oreothlypis celata)

Males of some oscine passerines learn and share songs of neighboring males. This process can lead to the formation of song pattern neighborhoods or microhabitat song dialects. The degree to which song sharing occurs between populations and the spatial scale over which neighboring males share songs, however, can vary widely, and interpopulation comparisons have suggested that song sharing is more common in residents than in migrants. Here, we examine two populations of the orange-crowned warbler (Oreothlypis celata) to quantify patterns of song sharing at the northern (long-distance migrant) and southern (short-distance migrant) edges of the breeding distribution and to test if return rate, territory fidelity, and breeding dispersal explain the patterns found in the two populations. The southern population (O. celata sordida breeding on Santa Catalina Island, California; 33°N) had a higher annual return rate to their territories and exhibited higher song sharing in neighborhoods than their counterparts (O. celata celata breeding in Fairbanks, Alaska; 64°N). Year-to-year patterns of territory fidelity and breeding dispersal distances were similar between populations. Our results suggest that if migratory distance generally covaries with the proportion of returning males, this could explain different levels of song sharing between the short- and long-distance migrants.     

Site fidelity and patterns of short- and long-term movement in the brilliant-thighed poison frog <Emphasis Type="Italic">Allobates femoralis</Emphasis> (Aromobatidae)

We studied movement and site fidelity of males and females of the territorial frog Allobates femoralis (Aromobatidae) in a population in the Nature Reserve “Les Nouragues” in French Guiana, South America. Observations during 3 months in 2006 ascertained intra-seasonal site fidelity for males and females. Males actively defend large multi-purpose territories whereas females retreat to small resting sites from where they commute to neighbouring males for courtship and mating. Female short-term movement corroborates the previous assumption of a polygynous or promiscuous resource-defence mating system. Year-to-year recaptures from 2005 until 2008 revealed distinct patterns of inter-annual movement for males and regional site fidelity for females. Males abandon their territories and have to re-negotiate them when reproduction starts again at the end of the dry season. Females are not subject to intra- or inter-sexual territorial competition and as a result move significantly less between reproductive seasons than males. Male long-term movement reflects spatial structure and prevailing social interactions and is a reliable indicator for tadpole deposition sites. The combined effects of intra- and inter-seasonal movement promote the diversity of mates for both sexes.     

The conflict between feeding and territorial defence in the great tit

Summary A field experiment investigated whether feeding and territorial defence competed for time in the activity budget of territorial male great tits during the spring. Feeding tables were placed on the territories of five males. Five other territorial males also fed at these tables, while ten additional males had no access to any feeding tables. A standardised intrusion using playback of territorial song and a stuffed mount of a male great tit was conducted on each of the twenty territories, and the response of the resident male measured. All of the males with access to a feeding table responded more vigorously to the intrusion than the males who received no extra food. These results are not attributable to the fact that males defended their territories more vigorously because of the addition of feeding tables, since males that gained extra food outside the boundaries of their own territories also defended more vigorously than birds with no access to a feeding table. The results support the conclusion that the provisioned males defended more vigorously because they could afford to take more time out from feeding.     

Past reproductive success affects future habitat selection

Correlational studies have shown that an individual's past reproductive success often increases its breeding site fidelity (i.e., the tendency to return to a previously occupied location), suggesting that individuals use their reproductive experience to assess habitat quality. However, the causality of the relationship between reproductive success and site fidelity is still uncertain. In a field experiment, the effect of mating success on site fidelity was isolated from potential confounding variables in a territorial dragonfly, the eastern amberwing (Perithemis tenera). The experiment controlled for site quality, intrinsic characteristics of males, previous territorial experience at the site, arrival order, and territorial evictions. Males that were prevented from mating were much more likely to change sites the following day than control males that were allowed to mate. This result was not affected by age, the amount of time a male spent on the site, or mortality. These results imply that individuals use their own reproductive success to assess the quality of the habitat. The benefit to an individual of using its reproductive success to determine habitat quality is discussed relative to other sources of information. Received: 31 May 1996 / Accepted: 31 January 1997     

Parental care of nestlings by male red-winged blackbirds

Summary Nestling feeding by males is less common among birds with polygynous mating systems than in monogamous species, because of the pronounced trade-off between parental behavior and the attraction of additional mates. In this study, however, we found that male red-winged blackbirds (Agelaius phoeniceus) commonly assisted females in feeding nestlings in several Ontario marshes. Male parental care was additional to that provided by females, and it significantly enhanced the fledging success of nests (Table 2). Male redwings did not help to feed all nests on their territories: primary and secondary nests were much more likely to receive male parental care than tertiary and later nests. Contrary to expectation, male parental care was not restricted to the nests of primary females: a greater proportion of secondary than primary nests were assisted (Tables 4a and b). The presence of new females settling on the territory at the same time that a resident female had nestlings, resulted in males deferring parental care until a later brood. This suggests that males trade off the recruitment of females against parental care to an existing brood. Although the number of nestlings fledging from a male's territory was strongly influenced by the number of females in the harem, males could additionally increase their reproductive success by feeding nestlings in one or more nests on their territories (Fig. 2). The reproductive success of females was significantly enhanced by male assistance in feeding nestlings (Table 3). However, those females not receiving male assistance on territories of feeding males did not suffer a significantly reduced reproductive success in comparison to females on territories of non-feeding males (Table 2). Males varied considerably in the quality of brood care given. We therefore suggest that the quality of male parental care may be a factor considered by females in choosing a breeding situation.     

Neighbor–stranger discrimination in Audubon's shearwater (Puffinus l. lherminieri) explained by a “real enemy” effect

Neighbor–stranger discrimination (NSD) occurs when animals respond with more aggression to strangers than to territorial neighbors. NSD has been reported in many species that defend multi-purpose territories for breeding and foraging, but it is rare among species that defend other types of territories. For birds that defend only their nest sites, there is no experimental evidence for NSD, and observational studies have provided mixed results. In a colony of Audubon's shearwaters (Puffinus l. lherminieri), I played back the calls of a neighbor and a stranger to males defending nest sites. Subjects responded with longer calls to playbacks of strangers than to those of neighbors. In shearwater colonies, strangers are often birds looking for future breeding sites. In contrast, there is no evidence that established breeders compete with their neighbors for any resources. Shearwaters should benefit from NSD because strangers represent a “real enemy” and established neighbors do not.