Mallard Use of Hen HousesTM in Eastern Ontario

Nesting structures for ground-nesting waterfowl may be an effective technique for increasing nesting success in regions in which nest success is below the 15% threshold needed to maintain a stable population. We studied the occupancy rate of artificial nesting structures called hen housesTM by Mallards (Anas platyrhynchos) nesting in two different wetland habitats, beaver ponds and sewage lagoons, in eastern Ontario during 1999–2001. We hypothesized that, because natural cover was sparse on sewage lagoons, Mallards would occupy hen houses at a higher rate on sewage lagoons than on beaver ponds. However, of the 248 hen houses distributed between beaver ponds and sewage lagoons, none was occupied by waterfowl. Common Grackles (Quiscalus quiscula) were the only avian species that nested in hen houses. However, Mallards successfully nested directly under several structures (n = 6) when water levels were low enough to expose the ground beneath them. Mayfield daily nest survival estimates for Mallards nesting in natural cover were similar on sewage lagoons and beaver ponds for all years (mean = 0.99) and were higher than most published estimates. Factors such as nesting cover, predation pressures, and structure design and material may influence the use of artificial hen houses and should be considered when planning a hen house program outside of the Prairie Pothole Region.

Costs of Reproduction in Breeding Female Mallards: Predation Risk during Incubation Drives Annual Mortality

The effort expended on reproduction may entail future costs, such as reduced survival or fecundity, and these costs can have an important influence on life-history optimization. For birds with precocial offspring, hypothesized costs of reproduction have typically emphasized nutritional and energetic investments in egg formation and incubation. We measured seasonal survival of 3856 radio-marked female Mallards (Anas platyrhynchos) from arrival on the breeding grounds through brood-rearing or cessation of breeding. There was a 2.5-fold direct increase in mortality risk associated with incubating nests in terrestrial habitats, whereas during brood-rearing when breeding females occupy aquatic habitats, mortality risk reached seasonal lows. Mortality risk also varied with calendar date and was highest during periods when large numbers of Mallards were nesting, suggesting that prey-switching behaviors by common predators may exacerbate risks to adults in all breeding stages. Although prior investments in egg laying and incubation affected mortality risk, most relationships were not consistent with the cost of reproduction hypothesis; birds with extensive prior investments in egg production or incubation typically survived better, suggesting that variation in individual quality drove both relationships. We conclude that for breeding female Mallards, the primary cost of reproduction is a fixed cost associated with placing oneself at risk to predators while incubating nests in terrestrial habitats.

What you find depends on where you look: responses to proximate habitat vary with landscape context

There is persistent interest in understanding responses of passerine birds to habitat fragmentation, but research findings have been inconsistent and sometimes contradictory in conclusions about how birds respond to characteristics of sites they occupy, such as habitat patch size or edge density. We examined whether these inconsistencies could result from differences in the amount of habitat in the surrounding landscape, e.g., for woodland birds, the amount of tree cover in the surrounding landscape. We compared responses of 22 woodland bird species to proximate-scale tree cover in open landscapes versus wooded landscapes. Our main expectation was that woodland birds would tolerate less suitable sites (less tree cover at the site scale) in open environments where they had little choice–where little tree cover was available in the surrounding area. We compared responses using logistic regression coefficients and loess plots in open and wooded landscapes in eastern North Dakota, USA. Responses to proximate-scale tree cover were stronger, not weaker, as expected, in open landscapes. In some cases the sign of the response changed from positive to negative in contrasting landscapes. We draw two conclusions: First, observed responses to proximate habitat measures such as habitat extent or edge density cannot be interpreted reliably unless landscape context is specified. Second, birds appear more selective, not less so, where habitat is sparse. Habitat loss and fragmentation at the landscape scale are likely to reduce the usefulness of local habitat conservation, and regional drivers in land-use change can have important effects for site-scale habitat use.