A new method for catching cavity‐nesting birds during egg laying and incubation

ABSTRACT The physiological condition of female birds during the egg‐laying and incubation periods is of considerable interest and yet is relatively understudied in wild birds, primarily due to the difficulty of catching birds during this period without causing nest desertion. We therefore developed a box‐net to capture cavity‐nesting birds using sections of a mist‐net placed around a metal cubic frame. We captured female Great Tits (Parus major) as they left nest boxes during the egg‐laying and incubation periods and measured desertion rates. Using box‐nets, we captured 108 of 119 (90%) females during egg laying and 10 of 12 (83%) during incubation. Our recapture rate over two consecutive days during incubation was 50% (5 of 10). Females not captured left nest boxes before we attempted to capture them, escaped through a hole in the mist‐net, or remained in nest boxes for more than 2 h, after which we ended capture attempts. Overall, 22% of egg‐laying females deserted, with desertion rates highest early in the egg‐laying period. Desertion rates of females captured using box‐nets did not differ from those of undisturbed females. One of 10 females captured in a box‐net deserted during the incubation period. Box‐nets are portable, can be set up and taken down quickly and easily, and could potentially be used with nest boxes or natural cavities at any height. Box‐nets are easy to construct and adaptable for use with an array of cavity‐nesting birds, and can be an important tool for studying female physiology during egg laying and incubation.     

Reproductive interactions of the Shiny Cowbird Molothrus bonariensis and the Yellow-hooded Blackbird Agelaius icterocephalus in Trinidad

The reproductive interactions of the Shiny Cowbird Molothrus bonariensis , a brood parasite, and the Yellow-hooded Blackbird Agelaius icterocephalus , a host of the cowbird, were studied In Trinidad, West Indies. We gathered information on the breeding biology of the Shiny Cowbird and the Yellow-hooded Blackbird, the frequency of use of the host species, and the effects of brood parasitism on host breeding success. Yellow-hooded Blackbirds are polygynous for the most part; males build nests and attempt to attract females to lay in them by means of song and visual displays directed towards the nests. This behaviour probably makes it easy for cowbirds to locate breeding birds and their nests. Cowbird eggs were found in 153 of 377 (40–3 %) blackbird nests located before the nestling stage. Shiny Cowbird parasitism of the Yellow-hooded Blackbird had little negative impact on host reproductive success, whereas predation accounted for the majority of nest failures. Vigilant nest defense by male blackbirds combined with colonial breeding apparently also minimized the extent of host egg damage and removal by cowbirds, and the parasitized and unparasitized nests were equally successful at producing blackbirds. Cowbirds most frequently parasitized the first or only nesting attempts in blackbird territories, and first or only nests were also successful more frequently than subsequent nests.     

Incubation recess behaviors influence nest survival of Wild Turkeys

In ground nesting upland birds, reproductive activities contribute to elevated predation risk, so females presumably use multiple strategies to ensure nest success. Identification of drivers reducing predation risk has primarily focused on evaluating vegetative conditions at nest sites, but behavioral decisions manifested through movements during incubation may be additional drivers of nest survival. However, our understanding of how movements during incubation impact nest survival is limited for most ground nesting birds. Using GPS data collected from female Eastern Wild Turkeys (n = 206), we evaluated nest survival as it relates to movement behaviors during incubation, including recess frequency, distance traveled during recesses, and habitat selection during recess movements. We identified 9,361 movements off nests and 6,529 recess events based on approximately 62,065 hr of incubation data, and estimated mean nest attentiveness of 84.0%. The numbers of recesses taken daily were variable across females (range: 1?7). Nest survival modeling indicated that increased cumulative distance moved during recesses each day was the primary driver of positive daily nest survival. Our results suggest behavioral decisions are influencing trade‐offs between nest survival and adult female survival during incubation to reduce predation risk, specifically through adjustments to distances traveled during recesses.     

Design and effectiveness of a novel trap for capturing nesting songbirds

ABSTRACT Capturing songbirds at their nests can be challenging and time consuming. Although traps designed for capturing songbirds at their nests have been described in the literature, few are effective for capturing species with open‐cup nests. We describe a cylindrical trap designed to capture songbirds at nests up to 2 m above ground in grasses, forbs, shrubs, and small saplings. The nest trap is constructed using a rigid hoop, two pieces of mist net, three stakes, and twist ties. We used this trap to capture female Dickcissels (Spiza americana) and female Indigo Buntings (Passerina cyanea) at their nests, with success rates of 85% (N= 196) and 60–73% (N= 16), respectively. Trapping success was comparable to that using other passerine nest trap designs. Nest abandonment after trapping attempts was rare and similar to that reported in previous studies. Our nest trap is lightweight, easy to make, versatile enough to use in a variety of grassland and shrub habitats, and easily carried and deployed in the field.     

Reproductive ecology of blackbirds ( Turdus merula maximus) in a high-altitude location, Tibet

Reproductive data of high-altitude blackbirds (Turdus merula maximus) were collected at an alpine environment covered with scrub vegetation in Lhasa mountains, Tibet. The blackbird nests were found from 3,800 to 4,500 m at a breeding density of 0.07 pairs/ha. Egg-laying occurred from early May to late July, with a peak (73.0% of all nesting attempts) between mid-May and mid-June. Most (79.5%) of the nests were sited in six different plant species with Cotoneaster microphyllus being most preferred. A few (20.5%) nests were against rocky walls. Bushes used for nest sites were significantly higher. Compared with lowland blackbirds, montane blackbirds experienced a shorter breeding season (2.5 months), laid smaller clutches (2–4 eggs, averaging 2.86), but larger eggs (mean volume index 16,348), produced only one brood per year, had a slightly shorter incubation period (12–13 days), but a longer nestling period (16–18 days), and enjoyed a higher breeding success (59.0%). In the alpine environment where climate is harsh and food supply poor, the strategy of increased egg size with decreased clutch size suggests that the high-altitude blackbirds improve their breeding success by investing more reproductive energy in fewer offspring in response to the constraints of time and resources. However, the environmental constraints on reproduction result in a low annual reproductive output.This revised version was published online in December 2004. The german abstract has been included.     

Costs and benefits of natal dispersal in yearling mallards Anas platyrhynchos

Costs and benefits of natal dispersal have not been fully evaluated in birds. We compared timing of breeding and nesting success for yearling female mallards Anas platyrhynchos returning to or dispersing from their natal areas. Information about natal origins was discerned with feather‐isotopes and combined with detailed reproductive histories for 503 radio‐marked females monitored at 16 study sites across the Canadian Aspen Parklands, during 1993–2000. A natal origin assignment model based on feather‐ δ³⁴S, δD, δ¹⁵N, and δ¹³C values correctly assigned 81% (112 of 138) of known‐source yearlings to region of origin; region‐specific rates ranged from 70–90%. Timing of breeding and nesting success was not related to whether or not a female had dispersed from its region of natal origin in Aspen Parkland (i.e. short‐distance dispersal) versus the southern prairies or boreal forest regions (i.e. long‐distance dispersal). Rather, nesting success was best modeled to include effects of site‐specific wetland and breeding pair abundances and an interaction between local breeding pair and wetland densities. Nest success performance relative to dispersal distance varied among study sites but was unrelated to local upland nest cover, wetland habitat conditions, or conspecific density. Thus, we detected no strong costs of dispersal but some evidence that long‐distance dispersers presumably benefitted when they were able to acquire better nest sites.     

Negotiation of parental care when the stakes are high: experimental handicapping of one partner during incubation leads to short-term generosity

1. Most game theoretical models of biparental care predict that a reduction in care by one partner should not be fully compensated by increased work of its mate but this may not be true for incubating birds because a reduction in care could cause the entire brood to fail.
2. I performed the first handicapping experiment of both males and females during incubation, by placing small lead weights on the tails of male and female northern flickers Colaptes auratus , a woodpecker in which males do most of the incubation.
3. Females responded to the acute stressor (handling and handicapping) by tending to abandon more readily than males and staying away from the nest longer in the first incubation bout. Among pairs that persisted, both males and females compensated fully for a handicapped partner, keeping the eggs covered nearly 100% of the time.
4. Partners did not retaliate by forcing their handicapped mate to sit on the eggs with a long incubation bout length subsequent to having a long bout length themselves. Instead, during the 24 h immediately after handicapping, males behaved generously by relieving handicapped females early.
5. Such generosity was probably not energetically sustainable as these male partners took on less incubation in the 72 h following handicapping compared to female partners of handicapped males. Males and females are probably generous in the short-term because of the high cost of nest failure during incubation but maintaining increased work loads in the longer term is probably limited by body condition and abandonment thresholds consistent with game theory models.     

Effect of alarm calling by male Red‐winged Blackbirds on nestling begging and female provisioning behavior

ABSTRACT Nestling begging and parental provisioning can attract nest predators and reduce reproductive success, so parents and their offspring might be expected to respond adaptively by minimizing predator‐attracting cues when predators threaten nests. Male Red‐winged Blackbirds (Agelaius phoeniceus) are well known for their antipredator alarm calls that contain information about the approach of potential nest predators. We examined the begging behavior of nestlings and the provisioning behavior of females in response to antipredator alarm calls of males to test the adaptive response hypothesis. Playback experiments provided no evidence that alarm calls function to switch off vocal begging; nestlings were equally likely to beg vocally during playback and control periods. Video recordings showed that male alarm calling had no significant effect on inappropriate vocal begging (in the absence of an adult), but significantly reduced the incidence of spontaneous calling (in the absence of begging). Adult females responded to male antipredator alarm calls by delaying their provisioning visits. In addition, although having no significant effect on use of nest‐arriving calls by females, male alarm calling significantly reduced their use of nest‐leaving calls. We conclude that nestling and female Red‐winged Blackbirds respond to male alarm calls in ways that might reduce the risk of predation, but nestlings beg vocally when females arrive to feed them, regardless of male alarm calling, perhaps to avoid a competitive disadvantage with broodmates.     

A male destroying an egg in a cooperative breeding attempt in Lesser Spotted Woodpecker Dendrocopos minor

A cooperative breeding case was found in Lesser Spotted Woodpecker (LSW) in which a male and three different females were involved. The contributions of each member of the cooperative breeding team were quantified during nest excavation and incubation. This is the first such report on LSW. During daytime, the nest was mainly occupied by the male during the final excavation phase, nest guarding, and egg laying. Aggressive interactions were recorded between two of the females during nest excavation, egg laying and incubation. The male was recorded destroying an egg presumably laid by the dominant female. The highest contribution during daytime incubation was made by the dominant female (39%), followed by the male (34%) and then by a second female (27%). The third female contributed very little at any stage. A picture of the male removing the egg was analyzed to estimate the egg maximum width, ruling out a possible runt egg. Motivations behind the behaviour of the male destroying the egg remain unclear.     

Predator density influences nest attendance of Yellow‐headed Blackbirds Xanthocephalus xanthocephalus

Nest attendance behaviour in birds is a function of the careful balance between the risk of nest predation and the needs of the parents and nestlings. This attendance must be carefully regulated, as increased parental activity at the nest increases nest predation risk. We tested the long‐standing hypothesis that nest predation risk influences parental behaviour by evaluating the influence of local Marsh Wren Cistothorus palustris density on the off‐bout frequency of Yellow‐headed Blackbirds Xanthocephalus xanthocephalus. Marsh Wren density was negatively correlated with Yellow‐headed Blackbird off‐bout frequency during the morning (05:00–10:00 h) and evening (16:00–21:00 h), suggesting that Yellow‐headed Blackbirds alter their nest attendance behaviour in response to a perceived increased risk of nest predation. We suggest that Yellow‐headed Blackbirds are sensitive to nest predation risk and alter their behaviour accordingly to increase overall fitness, although future research is needed to evaluate the influence of Marsh Wren nest predation on the reproductive success of Yellow‐headed Blackbirds.     

Nest Success of Gunnison Sage-Grouse in Colorado,USA

Gunnison Sage-Grouse (Centrocercus minimus) is a species of concern for which little demographic information exists. To help fill this information gap, we investigated factors affecting nest success in two populations of Gunnison Sage-Grouse. We assessed the relative effects of (1) vegetation characteristics (e.g., shrub height, shrub cover, grass cover, and grass height), (2) temporal factors (e.g., year, timing of incubation initiation, and nest age), (3) precipitation, and (4) age of the nesting female (yearling or adult) on nest success rates. We found 177 nests in the Gunnison Basin population (that contains 85–90% of the species) from 2005–2010 and 20 nests in the San Miguel population (that contains < 10% of the species) from 2007–2010. Temporal factors had the greatest impact on nest success compared to vegetation characteristics, precipitation, and female age. Nest success varied considerably among years ranging from 4.0%-60.2% in Gunnison Basin and from 12.9%- 51.9% in San Miguel. Nests that were initiated earlier in the breeding season had higher nest success (at least one egg hatches). Daily nest survival rates decreased during the course of incubation. None of the vegetation characteristics we examined were strongly related to nest success.     

Nest Crypsis, Reproductive Value of a Clutch and Escape Decisions in Incubating Female Mallards Anas platyrhynchos

In cryptically coloured birds, remaining on the nest despite predator approach (risk‐taking) may decrease the likelihood that the nest will be detected and current reproductive attempt lost. By contrast, flushing may immediately reveal the nest location to the predator. Escape decisions of incubating parents should therefore be optimized based on the risk‐to‐parent/cost of escape equilibrium. Animal prey may assess predation risk depending on a variety of cues, including the camouflage that vegetation provides against the predator. We examined interactive effects of nest crypsis and the current reproductive value of a clutch on flushing distances in incubating mallards (Anas platyrhynchos) approached by a human. Our results were consistent with predictions of parental investment theory: flushing distances were inversely correlated with measures of the reproductive value of the current clutch, namely with clutch size, stage of incubation and mean egg volume. Independently of a reproductive value of a clutch, nest concealment explained a significant portion of the variation in flushing distance among females; individual females tended to increase/decrease flushing distances according to change in nest cover. The results further suggest that vegetation concealment greatly influenced the risk of nest detection by local predators, suggesting that vegetation may act as a protective cover for incubating female. A female's ability to delay flushes according to the actual vegetation cover might thus be viewed as an antipredator strategy that reduces premature nest advertising to visually oriented predators. We argue, however, that shorter flying distances from densely covered sites might be maladaptive in areas where a predator's ability to detect incubating female does not rely on visual cues of nests.     

Incubation feeding by male Scarlet Tanagers: a mate removal experiment

ABSTRACT Incubation feeding, where males feed their mates, is a common behavior in birds and may improve female condition, nest attentiveness, and nesting success. We used behavioral observations and a temporary mate removal experiment to test the female nutrition hypothesis for incubation feeding by male Scarlet Tanagers (Piranga olivacea). All males (N= 20) were observed incubation feeding and fed females both at the nest (x? 1.36 trips/h) and away from the nest (x? 20.1 trips/h). Male feeding rate off‐nest was negatively correlated with the duration of female foraging bouts and positively correlated with the total time females spent incubating per hour. Eggs were predated at seven of 19 (37%) nests, but nest survival during incubation was not related to either female incubation behavior or male feeding rate. During temporary removal experiments (N= 12), female Scarlet Tanagers remained on the nest significantly longer and did not have longer foraging bouts. An unexpected outcome of the removal experiments was a dramatic change in female vocal behavior. All 12 experimental females gave chik‐burr calls during the male‐removal experiments (x? bout length = 11.7 min), but during normal observation periods only six of 20 females at the incubation stage gave chik‐burr calls (x? bout length = 0.7 min, N= 20). Our results suggest that female tanagers likely gain nutritional benefits from incubation feeding, but male feeding may not improve immediate reproductive success. Nine of 54 (17%) nestlings in five of 17 broods (29%) were extra‐pair young (EPY), indicating that males could potentially benefit from incubation feeding via mate retention and fidelity as well as, or instead of, through immediate gains in reproductive success. Our study indicates that females benefit from incubation feeding and do not simply passively accept food from their mates, but instead may influence male feeding rates through direct (e.g., mate following and vocalizing) and indirect (the threat of mate abandonment or cuckoldry) means.     

Columbian sharp-tailed grouse female and nest survival in northwestern Colorado

Wildlife management and conservation can be challenging when the demography of a focal species is unknown or limited given that fecundity and adult survival influence population growth. The Columbian sharp-tailed grouse (Tympanuchus phasianellus columbianus) have been reduced to ≤10% of their former range since the early 1900s. We conducted a 3-year study (2015–2017) across 4 study sites in northwestern Colorado, USA, to evaluate female hazard and nest survival. We trapped and marked 270 female sharp-tailed grouse and identified 275 nests for our hazard and survival analyses. Females during the breeding stage of the reproductive season experienced more hazard compared to the nesting and the early and late post-nesting stages for females without broods. Females experienced a higher degree of hazard during the breeding stage and mortality risk was >3 times higher than the nesting stage, >7 times higher than early post-nesting (EPN)-no brood stage, and >5 times higher than the late post-nesting (LPN)-unsuccessful stage. Two reproductive season stages (LPN-successful and EPN-brood) provided marginal inference. Nest incubation initiation date and nest age best described nest daily survival. Females that initiated incubation of initial nests earlier in the season experienced lower nest daily survival than later in the incubation season. Because female Columbian sharp-tailed grouse hazard varied among different reproductive season stages, we recommend that wildlife managers develop management actions that reduce hazard during the specific reproductive season stages (i.e., the breeding season). For Columbian sharp-tailed grouse in Colorado, we recommend that Colorado Parks and Wildlife collaborate with federal farm program agencies to implement a no-tillage restriction from 1 May through 30 June for active agricultural fields within 2 km of active Columbian sharp-tailed grouse leks to enhance nest survival.     

Nest shape explains variation in sexual dichromatism in New World blackbirds

Following Charles Darwin, research on sexual dichromatism has long focused on sexual selection driving ornamentation in males. However, Alfred Russel Wallace proposed another explanation – that dichromatism evolves as a result of selection favoring crypsis in incubating females. Many recent studies suggest that evolutionary changes in sexual dichromatism often result from changes in female, in addition to male, plumage, yet the evolutionary mechanisms driving changes in female plumage remain largely unexplained. To test Wallace's hypothesis, we examined variation in sexual dichromatism and nest shape, a proxy for predation risk, among New World blackbirds (Aves: Icteridae). Phylogenetic models reveal an evolutionary correlation between sexual dichromatism and nest exposure. Specifically, we found that transitions in monochromatic lineages with exposed nests toward either concealed nests or dichromatism were common. Although this evidence supports Wallace's hypothesis that female incubation leads to selection for crypsis or concealment, we also found that transitions to monomorphism were common, even in lineages with exposed nests – a result suggestive of a role for positive selection on female ornamentation. These patterns of plumage evolution support a growing body of work emphasizing the importance of developing and testing hypotheses to explain evolutionary changes in female, as well as male, ornamentation.     

Nest Defence Behaviour and Testosterone Levels in Female Pied Flycatchers

Nesting holes are a scarce resource for obligated cavity‐nesting birds and an important selective force for the evolution of aggressive female behaviours, which may be mediated by testosterone (T) levels. It is known that during periods of intense intrasexual competition such as initial breeding stages, females are highly aggressive towards intruding females. Here, we studied the implications of T levels for female–female competition by comparing levels of aggressiveness towards simulated female intruders (decoys) in two populations of the pied flycatcher (Ficedula hypoleuca) with a marked difference in breeding density. To this end, we exposed free‐living females to simulated territorial intrusions during 30 min when nest construction was almost complete. T levels of females were measured at the beginning of incubation under the assumption that they are positively associated with T levels during nest building. We also related aggressiveness to T levels in both populations. Furthermore, we aimed at detecting whether variation of T levels may explain female incubation attendance. Females showed higher T levels in the populations where pied flycatchers were exposed to a higher likelihood of conspecific interactions (high breeding density) than in the population with low breeding density. Female territorial presence, vigilance at the nest box and proximity to decoys were negatively related to circulating T levels in the high‐density population, but not in the low‐density population. Differences in T levels between populations did not result in differences in female incubation attendance, but T levels were negatively related to the incubation attendance in females from the population showing high T levels. In our populations, T levels in females prior to laying reflect the need to defend nesting cavities which is higher at high breeding density and in subdominant females. High T levels are costly in terms of incubation attendance.     

Nest temperature, incubation period, and investment decisions of incubating wood ducks Aix sponsa

Incubating birds must balance their energetic demands with the time needed to provide care to developing embryos. Reduced care by incubating parents can result in longer incubation periods that increase predation risk and potentially influence neonate phenotype. We measured nest temperature, incubation period, and body mass dynamics of female wood ducks Aix sponsa , and used an information-theoretic approach to investigate effects of several explanatory variables on incubation period and thermal characteristics of nests. A model that included clutch size and standard deviation of nest temperature best explained the variation in incubation period. Parameter estimates indicated that incubation period increased with increases in clutch size and standard deviation of nest temperature. Next, we examined relationships between maternal effects and the standard deviation of the nest temperature. The best fitting model included initiation date of incubation. There was little support for including early incubation body mass of females, incubation constancy, and percent change in female body mass in the model. The parameter estimate showed that standard deviation of nest temperature declined as initiation date of incubation advanced. Female body mass at the start of incubation was not related to structural size suggesting that heavy females were in better physical condition than were light females. Heavy females nested earlier and lost more body mass during incubation than light females, but heavy females did not reduce variation in nest temperature to decrease the incubation period. The fact that early nesting females in good physical condition did not shorten incubation periods by keeping nest temperatures less variable could have been due to either energetic limitations or restraints. Experimental manipulations of incubation costs will be needed to distinguish between these hypotheses.     

Age-specific reproductive performance of Black Grouse Tetrao tetrix females

As part of a demographic study of Black Grouse in the southern French Alps, we estimated variations in reproductive parameters in relation to age of females. Both yearlings and adults initiated a clutch, but adults raised about eight times more young (yearlings 0.25 chicks/females, adults 1.85 chicks/female). Yearlings laid significantly fewer eggs and initiated incubation later than older females. Success of nests did not differ between the two age classes, but yearlings tended to re-nest less frequently and exhibited higher chick loss than older females. The lower reproductive success of yearlings was primarily due to their lower ability to raise young. At nest sites, nest concealment, as well as vertical and horizontal structure and density of the vegetation, did not differ between yearling and older females, which is consistent with the similarity in nesting success in the two age classes. Results support the hypothesis that the extent of the difference in number of young raised by yearling and older females increases with predation pressure.     

Nest survival and productivity of the critically endangered Sociable Lapwing Vanellus gregarius

The Sociable Lapwing Vanellus gregarius is a critically endangered species, probably declining from 5000 pairs to 500 pairs in 11 years. Fieldwork was conducted at two sites in Kazakhstan, May–August 2004, to identify causes of the species’ decline. In total, 58 nests and a minimum of 36 broods in 16 colonies were found: colonies consisted of 1–8 nests that were on average 154 m apart, with 2.1 km between colonies. Although classified as biparental, the total proportion of time both parents spent incubating was low (77 ± 2% se, n = 13 nests). Daily survival rates (Mayfield method) were very low during incubation (0.943 ± 0.009 se) but high during the chick stage (0.986 ± 0.004 se); incubation and chick‐stage durations were found to be 28.5 and 29 days, respectively, so that the overall probability of any breeding attempt fledging chicks was 0.124 (0.055–0.274 95% confidence interval). A breeding attempt that produced fledglings, fledged 2.2 ± 0.2 se chicks (n = 26) on average. Observed productivity predicted the population decline over the last 11 years well (using the maximum number of nesting attempts per pair of 1.4 that could have occurred in this study, and assuming an adult and first‐year survival rate of 0.74 and 0.60, respectively, based on the means for Northern Lapwing Vanellus vanellus and Golden Plover Pluvialis apricalia). Nest survival during incubation (controlling for colony effects) may have been longer for nests in predominantly Artemisia rather than grass habitat. Mean nest survival for a colony was higher in areas with more bare ground and more nest predators, suggesting that predators were relatively unimportant in nest (egg or chick) mortality, but was lower in areas with high numbers of cattle, suggesting that trampling was important (64% of known‐cause nest failures, n = 11, were trampled). Nests were preferentially sited in areas of Artemisia, where there was greater dung abundance, and probably shorter vegetation, suggesting that highly grazed vegetation is important for nesting. Chicks preferentially selected areas with a lower percentage of bare ground and possibly taller vegetation, suggesting that more vegetated areas are important for chicks. The results suggest that low egg survival due to nesting in areas of high grazer density may be responsible for the Sociable Lapwing's decline. Although grazers may create suitable vegetation for initial nesting, if those grazers remain at high density as in anthropogenic systems then they may reduce nest survival, probably through trampling. Experimentally maintaining grazing early but reducing it later in the breeding season is the logical first step in managing the species to increase egg survival and so to increase productivity.