Rates Of Nest Loss Research Articles

Conspecific brood parasitism in the tropics: an experimental investigation of host responses in common moorhens and American purple gallinules

Species occupying a broad latitudinal range may show greater phenotypic plasticity in behavior than species with smaller ranges or more specific habitat requirements. This study investigates for the first time the occurrence of conspecific brood parasitism (CBP) in sympatric tropical populations of the common moorhen (Gallinula chloropus pauxilla Bangs) and the American purple gallinule (Porphyrula martinica L.). CBP occurred in at least 20% (N = 76) of common moorhen nests on the Rio Chagres in Panama. Half (N = 20) of the parasitic eggs were accepted, but 10 were destroyed or ejected from host nests. Introductions of experimental eggs into nests revealed hosts were more likely to accept parasitism later in the host's laying period and during incubation, consistent with expectation of an adaptive response. CBP was not detected in a small sympatric population of American purple gallinules. Members of this population did not eject experimental eggs, suggesting a lack of experience with costly CBP. Contrasting ecological factors help explain why these two species of rail (Family Rallidae) differ in regard to CBP. Purple gallinule territories were sparse, owing to the distribution of preferred habitat. Moorhens flocked outside of the breeding season. They nested more synchronously, at higher densities, and primarily in ephemeral floating vegetation. Further, moorhens suffered a rate of nest loss nearly double that of American purple gallinules, and this increased over the course of the breeding season. Moorhen clutches were larger on average, and more variable in size than those of purple gallinules. Reproductive effort and rate (seasonality) constitute important life history differences between these species that may constrain the evolution of reproductive tactics. Comparing these sympatric populations, and others differing in life-history traits and ecological constraints, highlights the role of risk management in the evolution of CBP.

Sources of variation in the nesting success of understory tropical birds

Survival of offspring is a key fitness component and, for birds, the threat of predation on nests is especially influential. Data on rates of nest success from tropical regions are comparatively few, conservation‐relevant, and essential for assessing the validity of models comparing the life histories and behavior or birds across latitudinal gradients. We monitored over 2 000 nests in the lowland forests of central Panama and, using the logistic exposure to model the fate of nests, explored the importance of variation in rate of nest success according to type of nest, height of nests, among years, in early versus late nests, and at different stages of the nest cycle. Analyses of over 1 400 nests for 18 species revealed considerable variation among species in the daily survival rate of nests (range among 18 species=0.91 to 0.98), but nest type and stage of the nesting cycle were generally influential on the probability of nest success. Cavity or enclosed nesters experienced greater nest success than open cup nesters and rates of nest loss were generally greatest in the nestling stage. We found limited evidence that height of nests affected probability of success, but no indication that timing of nesting effort was influential. Despite the occurrence of a severe ENSO event during our sampling, annual variation in nest success was not consistent among species. Interspecific variation in the rates and patterns of nest predation in our study, coupled with reports of high rates of nest loss at temperate latitudes, lead us to question long standing assumptions about latitudinal trends in rates of nest loss. We urge further work to understand the implications of nest predation on the evolutionary ecology of tropical birds.

Male mate choice, male availability and egg production as limitations on polyandry in the red-necked phalarope

In sequentially polyandrous birds, a female's second mate faces a substantial risk of cuckoldry due to rapid mate switching and stored sperm. Secondary males are potentially available to females because males arrive asynchronously and/or are recycled into the breeding pool following nest predation. In a study of red-necked phalaropes, Phalaropus lobatus, a sex-role reversed shorebird, we tested the hypotheses that the proportion of females that become polyandrous is proximately limited by: (1) the ability of females to produce eggs, (2) the availability of males as mates and (3) male mate choice. In a colour-banded population in which rates of nest loss were manipulated by researchers, females that produced second clutches required similar lengths of time to complete clutches as those contemporaneously producing first clutches, and increased their egg size relative to their first clutch, making egg limitation unlikely. There was no correlation between an annual measure of males' availability as potential mates following nest losses and the proportion of females that were polyandrous. The majority of males that lost clutches (66%) re-paired with their original female significantly more often than expected by random mate choice ( P<0.0001). Although 76% of polyandrous nestings involved renesting males, only 6% ( N=46) of renesting males changed mates if their original female was still available. Renesting males that changed mates did not select for or against females that had already produced clutches (NS). Our results suggest that the level of polyandry in this species is not constrained by the females' abilities to produce more eggs or by the number of males recycling back into the breeding pool. Instead, the proportion of females that become polyandrous is limited by males choosing to renest with their original females, thereby decreasing their probability of caring for eggs potentially fertilized by a female's previous mate.

SURVIVAL RATES OF A NEOTROPICAL PARROT: IMPLICATIONS FOR LATITUDINAL COMPARISONS OF AVIAN DEMOGRAPHY

Latitudinal variation in avian demography played an important early role in the development of life history theory, especially in the idea of a cost of reproduction. Recent attempts to determine the survivorship of tropical birds with mark-recapture sta- tistics have proved controversial. Here, we use a small neotropical bird, the Green-rumped Parrotlet (Forpus passerinus), as a model system for investigating sources of heterogeneity that might bias interspecific comparisons. Mark-resighting data were collected on 1334 adult parrotlets over a decade. We expected adult survival to be low because this parrot lays a large clutch (mean 5 7 eggs), is a cavity nester, and breeds in a highly seasonal environment. A two-age-class term in local survival was nonsignificant, indicating that an age or transience effect was unimportant. Local survival of males did not vary annually, but 19.3% of the yearly variation in female survival was explained by rates of nest loss during stages when females were incubating or brooding young. The overall local survival rate of parrotlets ( f5 0.565) was identical to temperate hole-nesting species of the same body size but was lower than that of tropical birds that lay smaller clutches. However, we also detected considerable heterogeneity in parrotlet survival. Females and males that were sighted but did not breed comprised a mean 23.5% and 52.9% of our population, respec- tively. Using multistate models, we found that breeders had significantly higher probabilities of local survival ( f5 0.678 vs. 0.486), of retaining their status as breeders ( c5 0.719 vs. 0.279), and of detection ( p 5 0.997 vs. 0.375) than did nonbreeders. Overall, males and females had comparable local survival rates (breeders f5 0.698 vs. 0.658, nonbreeders f5 0.536 vs. 0.436). Our estimates of local survival could be affected by breeding dispersal, but site fidelity of parrotlets was strong: 95% of adults moved ,500 m in consecutive years. A literature review for tropical birds showed that mark-resighting studies usually report return rates based on resightings of breeding or territorial adults, whereas mist net studies rely on recaptures and pool birds of different age and social status in their calcu- lations of local survival. Future studies should attempt to compare subsets of avian pop- ulations that are similar in demography. Because rates of site fidelity and social system may differ among species, these factors must also be considered in interspecific comparisons of avian life histories.

Higher rate of nest loss among primary than secondary females: infanticide in the great reed warbler?

An individually marked population of great reed warblers Acrocephalus arundinaceus was studied between 1984 and 1991 in South Central Sweden. The fates of 279 nests were analysed for the 25 days following clutch initiation. The average frequency of nest loss (43%) did not differ significantly between years or between four periods of the breeding season. After a breeding failure, 70% of the females laid a replacement clutch, most of them together with the same male. On polygnous territories, males assisted the female who first hatched young regardless of her initial mating status (Fig. 2). According to the acutal status of the females attending the nests, for each day nests were classified as being of either monogamous (M), primary (P) or secondary (S) status. From egg-laying to fledging the rate of nest loss decreased among nests of primary status whereas it increased among nests of monogamous and secondary status. During the egg-laying period, the rate of nest loss was 3 times higher among nests of primary than among nests of monogamous and secondary status (Fig. 3). Thus, the high loss level among nests of primary status during the laying period was closely associated with the presence of a female with a less advanced nest on the territory. All nests were situated in reed beds above deep water and most of them at a height at which possible inter-specific nest predators would have caused disturbance to the nest itself. The suspicion that secondary females committed sexually selected infanticide was supported by an experiment with dummy eggs that revealed bill peck markings identical to those obtained from great reed warblers (Fig. 4).

Higher rate of nest loss among primary than secondary females: infanticide in the great reed warbler?

Higher rate of nest loss among primary than secondary females: infanticide in the great reed warbler?

Effects of Olfactory Cues on Artificial-Nest Experiments

We examined the effects of two potential olfactory cues on the outcome of experiments using artificial nests to assay predation on open-cup nesting songbirds. In two experiments lasting 15 days each and replicated two times at three sites, bamboo nests baited with Japanese Quail (Corturnix japonica) eggs were placed on the ground in a 5 x 4 grid array with 50 m between adjacent nests. Egg survivorship was monitored every five days, and remote cameras were used to take photographs of animals removing bait eggs from nests. One experiment consisted of four treatments that varied the type and amount of olfactory information provided by the investigator: (1) human (2) no scent; (3) scent; and (4) perfume. Artificial scents were applied to shoes, clothing, and skin during the ex- periment set-up and monitoring. For the first experiment, rates of nest loss were greater for the human-scent treatment than deer-scent and/or no-scent treatments in one-half of the spatial/temporal replicates. Rain appears to have complicated the effects of the scent treat- ments in some of the spatial/temporal replicates. Final levels of nest loss, however, were greater for perfume and human-scent treatments than deer-scent and no-scent treatments regardless of spatial/temporal replicate. The second experiment consisted of two treatments, one in which eggs were replaced periodically, and the other in which eggs were not replaced for the duration of the experiment. Both treatments had similar rates and final levels of nest loss. Approximately 90% of 51 photographs were of olfactory-searching, predominantly noc- turnal mammals. We conclude that olfactory-searching predators can cue on human odors left in the area of artificial nests, but that either rain or scents (e.g. the deer scent) can be used to decrease this potential bias. In contrast, changing egg qualities over the time scale