Indirect, physiological assessment of reproductive state and breeding chronology in free‐living birds: an example in the Marbled Murrelet (Brachyramphus marmoratus)

Abstract

Summary1. An indirect, physiological method to assess reproductive state in individuals of unknown status is described. The plasma levels of two main yolk precursors, vitellogenin (VTG) and very-low density lipoproteins (VLDL), are focused on as indices of egg production, for the characterization of fecund females. 2. Data for a species where breeding chronology could be directly assessed, at the population level (Cassin's Auklet, Ptychoramphus aleuticus ), confirmed the validity of this approach: plasma VTG levels were highest during the defined egg-laying period, and the highest proportion of females were defined as 'egg-producing' in this period. 3. Analysis of samples for Marbled Murrelets ( Brachyramphus marmoratus ) caught off-nest (i.e. where all individuals were of unknown status), clearly identified a putative egg-laying phase, with a single, protracted laying period (cf. multiple-broodiness). 4. Analysis of body mass confirmed our characterization of 'egg-producing' females: birds with elevated plasma VTG were on average 40 g heavier than other females, equivalent to the mass of the single egg (36-41 g). 5. Indirect, physiological assessment of reproductive state provided valuable information on the breeding biology of Marbled Murrelets which would have been difficult to obtain in any other way (e.g. proportion of fecund females, breeding phenology, single vs multiple-clutch breeding pattern). Despite some limitations, this technique should be applicable to any oviparous vertebrate population where essential information on breeding biology cannot be obtained by more traditional methods.

Individual variation in body burden, lipid status, and reproductive investment is related to maternal transfer of a brominated diphenyl ether (BDE-99) to eggs in the zebra finch

“…During egg production the lipid status of laying females changes dramatically due to the hepatic synthesis and secretion into plasma of large amounts of the lipid-rich yolk precursors (vitellogenin and very-low-density lipoproteins [VLDLs]) that serve as the main source of yolk lipids [9]. For example, plasma lipid concentrations increase from approximately 3 mg/ml in non-laying turkeys (Meleagris gallopavo) to 21 mg/ml in laying turkeys [10], and similar changes have been documented in free-living birds [11][12][13]. Importantly, there is marked interindividual variation (8-10-fold) in plasma yolk precursor levels for any given egg or follicle size [14].…”

Relating Microclimate to Epiphyte Availability: Edge Effects on Nesting Habitat Availability for the Marbled Murrelet

“…These include Desolation Sound , Lougheed 2000, Bradley 2002), Clayoquot Sound , Kelson et al 1995, Mason et al 2002, Barkley Sound (Carter 1984, Carter andSealy 1990) and the West Coast Trail coast (Burger 1997b) in BC, and several studies outside BC (Kuletz 1996, Speckman et al 2000. By contrast, Strong et al (1995) found significant shifts in distribution along the entire Oregon coast from year to year.…”

“…Most of these nests were in BC and Oregon. Three measures of fecundity, derived from three different methods, are available from the Sunshine Coast, BC (including Desolation Sound) for the period 1994-2000, and are compared here (Manley 1999, Lougheed 2000. Manley (1999) observed 68 nesting attempts, using ground observations and tree climbing, and reported nest success as 0.33 fledglings per nest.…”

“…The ratio of HY:AHY is also known as the productivity index (Kuletz and Kendall 1998). For the following reasons, comparisons of HY and AHY birds are likely to contain systematic errors and the productivity index needs adjustments to be reliably used as a measure of at-sea fecundity (Kuletz and Kendall 1998, Kuletz and Piatt 1999, Lougheed 2000, Lougheed et al 2002b):…”

“…The same is true for variations in temporal scales (seconds to decades). Murrelets show strong diurnal and seasonal variations in their distribution at sea (Carter and Sealy 1990, Rodway et al 1995, Gaston 1996, Lougheed 2000, Speckman et al 2000 which can mask patterns in habitat use if the study protocol does not take them into account.…”